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Clinical vignettes for the usmle step 1   pre test self-assessment and review uploaded by www.fomscu-forum.com Clinical vignettes for the usmle step 1 pre test self-assessment and review uploaded by www.fomscu-forum.com Document Transcript

  • PRE TEST ® Clinical Vignettes for the USMLE Step 1 PreTest® Self-Assessment and Review
  • Notice Medicine is an ever-changing science. As new research and clinical experience broaden our knowledge, changes in treatment and drug therapy are required. The authors and the publisher of this work have checked with sources believed to be reliable in their efforts to provide information that is complete and generally in accord with the standards accepted at the time of publication. However, in view of the possibility of human error or changes in medical sciences, neither the authors nor the publisher nor any other party who has been involved in the preparation or publication of this work warrants that the information contained herein is in every respect accurate or complete, and they disclaim all responsibility for any errors or omissions or for the results obtained from use of the information contained in this work. Readers are encouraged to confirm the information contained herein with other sources. For example and in particular, readers are advised to check the product information sheet included in the package of each drug they plan to administer to be certain that the information contained in this work is accurate and that changes have not been made in the recommended dose or in the contraindications for administration. This recommendation is of particular importance in connection with new or infrequently used drugs.
  • PRE TEST ® Clinical Vignettes for the USMLE Step 1 PreTest® Self-Assessment and Review Second Edition McGraw-Hill Medical Publishing Division New York Chicago San Francisco Lisbon London Madrid Mexico City Milan New Delhi San Juan Seoul Singapore Sydney Toronto
  • Copyright © 2002 by The McGraw-Hill Companies, Inc. All rights reserved. Manufactured in the United States of America. Except as permitted under the United States Copyright Act of 1976, no part of this publication may be reproduced or distributed in any form or by any means, or stored in a database or retrieval system, without the prior written permission of the publisher. 0-07-141814-8 The material in this eBook also appears in the print version of this title: 0-07-137376-4 All trademarks are trademarks of their respective owners. Rather than put a trademark symbol after every occurrence of a trademarked name, we use names in an editorial fashion only, and to the benefit of the trademark owner, with no intention of infringement of the trademark. Where such designations appear in this book, they have been printed with initial caps. McGraw-Hill eBooks are available at special quantity discounts to use as premiums and sales promotions, or for use in corporate training programs. For more information, please contact George Hoare, Special Sales, at george_hoare@mcgraw-hill.com or (212) 904-4069. TERMS OF USE This is a copyrighted work and The McGraw-Hill Companies, Inc. (“McGraw-Hill”) and its licensors reserve all rights in and to the work. Use of this work is subject to these terms. Except as permitted under the Copyright Act of 1976 and the right to store and retrieve one copy of the work, you may not decompile, disassemble, reverse engineer, reproduce, modify, create derivative works based upon, transmit, distribute, disseminate, sell, publish or sublicense the work or any part of it without McGraw-Hill’s prior consent. You may use the work for your own noncommercial and personal use; any other use of the work is strictly prohibited. Your right to use the work may be terminated if you fail to comply with these terms. THE WORK IS PROVIDED “AS IS”. McGRAW-HILL AND ITS LICENSORS MAKE NO GUARANTEES OR WARRANTIES AS TO THE ACCURACY, ADEQUACY OR COMPLETENESS OF OR RESULTS TO BE OBTAINED FROM USING THE WORK, INCLUDING ANY INFORMATION THAT CAN BE ACCESSED THROUGH THE WORK VIA HYPERLINK OR OTHERWISE, AND EXPRESSLY DISCLAIM ANY WARRANTY, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. McGraw-Hill and its licensors do not warrant or guarantee that the functions contained in the work will meet your requirements or that its operation will be uninterrupted or error free. Neither McGraw-Hill nor its licensors shall be liable to you or anyone else for any inaccuracy, error or omission, regardless of cause, in the work or for any damages resulting therefrom. McGraw-Hill has no responsibility for the content of any information accessed through the work. Under no circumstances shall McGraw-Hill and/or its licensors be liable for any indirect, incidental, special, punitive, consequential or similar damages that result from the use of or inability to use the work, even if any of them has been advised of the possibility of such damages. This limitation of liability shall apply to any claim or cause whatsoever whether such claim or cause arises in contract, tort or otherwise. DOI: 10.1036/0071418148
  • For more information about this title, click here. Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii Block 1 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Block 2 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Block 3 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Block 4 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 Block 5 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Block 6 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 Block 7 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135 Block 8 50 questions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 157 Block 1 Answers, Explanations, and References. . . . . 181 Block 2 Answers, Explanations, and References. . . . . 201 Block 3 Answers, Explanations, and References. . . . . 219 Block 4 Answers, Explanations, and References. . . . . 237 Block 5 Answers, Explanations, and References. . . . . 253 Block 6 Answers, Explanations, and References. . . . . 271 Block 7 Answers, Explanations, and References. . . . . 291 Block 8 Answers, Explanations, and References. . . . . 311 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 v Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • Preface The current format of the United States Medical Licensing Examination (USMLE) Step 1 emphasizes clinical vignettes as the primary test questions. The examination is 400 questions, broken into eight blocks of 50 questions each. Examinees have one hour to complete each block. Clinical Vignettes for the USMLE Step 1: Second Edition parallels this format. The book contains 400 clinical-vignette-style questions covering the basic sciences and assembled based on the published content outline for the USMLE Step 1. The questions are divided into eight blocks of 50 questions. As on the Step 1 exam, each block tests the examinee in all basic science areas. Halfway through each block, a stopwatch set at 30 minutes is included to remind the examinee of the one-hour limit. Answers are in the second half of the book. Each answer is accompanied by a concise but comprehensive explanation and is referenced to a key textbook and/or journal article for further reading. The questions in this book were culled from the nine PreTest® Basic Science books. The publisher acknowledges and thanks the following authors for their contributions to this book: Anatomy, Histology, & Cell Biology: Robert Klein, Ph.D. and James C. McKenzie, Ph.D. Behavioral Sciences: Michael H. Ebert, M.D. Biochemistry & Genetics: Golder Wilson, M.D. Microbiology: Richard C. Tilton, Ph.D. Neuroscience: Alan Siegel, Ph.D. and Heidi Siegel, M.D. Pathology: Earl Brown, M.D. Pathophysiology: Maurice Mufson, M.D. Pharmacology: Arnold Stern, M.D., Ph.D. Physiology: James C. Ryan, Ph.D. and Michael Wang, Ph.D. McGraw-Hill August 2001 vii Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • PRE TEST ® Clinical Vignettes for the USMLE Step 1 PreTest® Self-Assessment and Review
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  • BLOCK 1 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • BLOCK 1 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Questions 1-1. A 6-year-old boy has received a deep puncture wound while playing in his neighbor’s yard. His records indicate that he has had the standard DPT immunizations and a booster when he entered school. What is the most appropriate therapy for this child? a. b. c. d. e. Tetanus toxoid Tetanus antitoxin Both toxoid and antitoxin at the same site Toxoid and antitoxin at different sites No treatment 1-2. A 67-year-old male presents with a slowly growing lesion that involves the lower portion of his left lower eyelid. You examine the lesion and find it to be a pearly papule with raised margins and a central ulcer (rodent ulcer). Histologic sections from this lesion would most likely reveal a. b. c. d. e. Reactive epidermal cells surrounding a central superficial ulcer Infiltrating groups of basaloid cells with peritumoral clefting Infiltrating groups of eosinophilic cells with keratin formation Dermal aggregates of small cells histologically similar to oat cell carcinoma An in situ lesion with full-thickness epidermal atypia 3
  • 4 Clinical Vignettes for the USMLE Step 1 1-3. Calcification of the internal carotid artery, which impinges upon the lateral half of the right optic nerve prior to its entrance to the brain of a 68year-old woman, results in certain visual deficits. The most likely visual deficits will be a. b. c. d. e. Total blindness of the right eye Right nasal hemianopsia Right homonymous hemianopsia Right bitemporal hemianopsia Right upper homonymous quadrantanopia 1-4. An HIV-positive patient asks if you can tell him the chances of him progressing to symptomatic AIDS. Which one of the following tests would be most useful? a. b. c. d. e. CD4 lymphocyte count HIV antibody test HIV RT PCR Neopterin HIV p24 antigen 1-5. An adult patient presents with the sudden onset of massive diarrhea. Grossly, this individual’s stool has the appearance of “rice-water” because of the presence of flecks of mucus. Cultures of this patient’s stool grow Vibrio cholerae, a curved, gram-negative rod that secretes an enterotoxin consisting of a toxic A subunit and a binding B subunit. The cholera enterotoxin causes massive diarrhea by a. b. c. d. e. Inhibiting the conversion of Gi-GDP to Gi-GTP Inhibiting the conversion of Gs-GTP to Gs-GDP Stimulating the conversion of Gi-GDP to Gi-GTP Stimulating the conversion of Gs-GDP to Gs-GTP Stimulating the conversion of Gs-GTP to Gs-GDP 1-6. A 26-year-old female with acquired immunodeficiency syndrome (AIDS) develops cryptococcal meningitis. She refuses all intravenous medication. Which antifungal agent can be given orally to treat the meningeal infection? a. b. c. d. Ketoconazole Amphotericin B Fluconazole Nystatin
  • Block 1 Questions 5 1-7. Methicillin-resistant S. aureus (MRSA) was isolated from 7 patients in a 14-bed intensive care unit. All patients were isolated and the unit closed to any more admissions. Which one of the following reasons best explains these rigorous methods to control MRSA? a. MRSA is inherently more virulent than other staphylococci b. The alternative for treatment of MRSA is vancomycin, an expensive and potentially toxic antibiotic c. MRSA causes toxic shock syndrome d. MRSA spreads more rapidly from patient to patient than antibiotic-susceptible staphylococci do e. MRSA is resistant to penicillin Questions 1-8 through 1-10 A 43-year-old male is recovering from an infectious disease and experiences a marked instability in his blood pressure with episodes of spiking of blood pressure. After a series of extensive examinations, it was concluded that this disorder was due to the effects of the infectious agent upon a component of the peripheral nervous system. 1-8. Logical sites where an infectious agent could produce such an effect include the a. b. c. d. e. Superior ganglia of cranial nerves IX and X Geniculate and trigeminal ganglia Otic and superior salivatory ganglia Carotid sinus and aortic arch Carotid and aortic bodies 1-9. The (appropriate) receptors situated in the sites listed in question 1-8 respond best to: a. b. c. d. e. Stretch Change in chloride ion concentration Contractions of the gut Decrease in oxygen concentration Increase in carbon dioxide concentration
  • 6 Clinical Vignettes for the USMLE Step 1 1-10. Neurons situated in the (appropriate) sites indicated in question 1-8 mediate their effects by projecting directly to the: a. b. c. d. e. Trigeminal spinal nucleus Fastigial nucleus Midbrain reticular formation Solitary nucleus Autonomic nuclei of the facial nucleus (cranial nerve VII) 1-11. A four-day-old male infant weighing 7 lb, 6 oz is brought to the emergency room by his parents. The examining emergency room physician notes that his skin and sclerae are icteric. A blood test indicates elevated unconjugated bilirubin in the serum. The elevated bilirubin levels in this patient are most likely the result of a. b. c. d. e. Deficiency of enzymes regulating bilirubin solubility Hepatocellular proliferation Decreased destruction of red blood cells Dilation of the common bile duct Increased hepatocyte uptake of bilirubin 1-12. A 39-year-old male with aortic insufficiency and a history of no drug allergies is given an intravenous dose of antibiotic as a prophylaxis preceding the insertion of a valve prosthesis. As the antibiotic is being infused, the patient becomes flushed over most of his body. What antibiotic was given? a. b. c. d. e. Vancomycin Gentamicin Erythromycin Penicillin G Tetracycline 1-13. For almost three years, a 50-year-old woman has been caring for her mother who is chronically ill with Alzheimer’s disease. A recent immunologic assessment of the caregiver daughter found that her a. b. c. d. e. Cellular immune system control of latent viruses was poor Percentage of T lymphocytes was high Helper/suppressor ratio was higher than normal Circulating neutrophils were decreased in number Natural killer cells were higher in number
  • Block 1 Questions 7 1-14. An anemic patient has the following red cell indexes: mean corpuscular volume, 70 mm3; mean corpuscular hemoglobin, 22 pg; and mean corpuscular hemoglobin concentration, 34%. These values are most consistent with a diagnosis of a. b. c. d. e. Folic acid–deficiency anemia Iron-deficiency anemia Pernicious anemia Sideroblastic anemia Thalassemia minor 1-15. A 26-year-old female with reactive depression complains of missing her period and having milk discharge from her breasts. She has no signs of pregnancy, including a negative pregnancy test. Which of the following might have caused these findings? a. b. c. d. e. Clomipramine Amoxapine Fluoxetine Mirtazapine Tranylcypromine 1-16. A young skier with normal pulmonary function (minute volume 4 L; pulmonary blood flow 5 L/min) who is recovering from a tibial fracture suddenly develops right-sided chest pain and tachypnea. Embolic occlusion of the right pulmonary artery is suspected. Which of the following alveolar gas measurements would immediately confirm the diagnosis? a. b. c. d. e. PO2 (mmHg) 125 125 100 80 80 PCO2 (mmHg) 60 20 40 20 60 1-17. A 22-year-old female carrying a preterm pregnancy (33 weeks) is in labor. Which of the following drugs can be given to the mother to promote fetal lung maturity? a. b. c. d. e. Betamethasone Fludrocortisone Metyrapone Spironolactone Triamcinolone
  • 8 Clinical Vignettes for the USMLE Step 1 1-18. This HIV-positive patient with a viral load of 750,000 copies of HIV RNA/ml and a total CD4 count of 50 is at an increased risk for a number of infectious diseases. For which of the following diseases is the patient at no more added risk than an immunocompetent host? a. b. c. d. e. Pneumocystic pneumonia Mycobacterial disease Kaposi’s sarcoma Pneumococcal pneumonia Herpes simplex virus 1-19. A 20-year-old male with herpes simplex of the lips is treated with famciclovir. What is the mechanism of action of famciclovir? a. b. c. d. e. Cross-linking of DNA Strand breakage of DNA Inhibition of viral DNA synthesis Inhibition of nucleotide interconversions Inhibition of a viral kinase 1-20. A child has ingested cyanide from her parents’ garage and is rushed to the emergency room. Which of the following components of the citric acid cycle will be depleted first in this child? a. b. c. d. e. NAD+ cofactor Citrate synthase Aconitase Citrate production Acetyl coenzyme A (CoA) production 1-21. Analysis of a patient’s stool reveals small structures resembling rice grains; microscopic examination shows these to be proglottids. The most likely organism in this patient’s stool is a. b. c. d. e. Enterobius vermicularis Ascaris lumbricoides Necator americanus T. saginata Trichuris trichiura
  • Block 1 Questions 9 1-22. A Nigerian medical student studying in the United States develops hemolytic anemia after taking the oxidizing antimalarial drug pamaquine. This severe reaction is most likely due to a. b. c. d. e. Glucose-6-phosphate dehydrogenase deficiency Concomitant scurvy Vitamin C deficiency Diabetes Glycogen phosphorylase deficiency 1-23. A person ascends to the top of a mountain where the atmospheric pressure is below normal. Which one of the following blood gases was drawn from the person at the top of the mountain? PO2 a. b. c. d. e. PCO2 50 60 80 100 120 30 40 50 40 30
  • 10 Clinical Vignettes for the USMLE Step 1 1-24. A 2-week-old baby is hospitalized for inadequate feeding and poor growth. The parents are concerned by the child’s weak cry. An experienced grandmother accompanies them, saying she thought the cry sounded like a cat’s meow. The grandmother also states that the baby doesn’t look much like either parent. The physician orders a karyotype after noting a small head size (microcephaly) and subtle abnormalities of the face. Which of the results pictured below is most likely? a. b. c. d. e. Result A Result B Result C Result D Result E A
  • Block 1 B C Questions 11
  • 12 D E Clinical Vignettes for the USMLE Step 1
  • Block 1 Questions 13 1-25. A 34-year-old female presents with recurrent episodes of severe headaches, palpitations, tachycardia, and sweating. A physical examination reveals her blood pressure to be within normal limits; however, during one of these episodes of headaches, palpitations, and tachycardia, her blood pressure is found to be markedly elevated. Workup finds a small tumor of the right adrenal gland. Which one of the following is most likely to be increased in the urine of this individual? a. b. c. d. e. Acetone Aminolevulinic acid (ALA) Hydroxy-indoleacetic acid (HIAA) N-formiminoglutamate (FIGlu) Vanillylmandelic acid (VMA)
  • 14 Clinical Vignettes for the USMLE Step 1 YOU SHOULD HAVE COMPLETED APPROXIMATELY 25 QUESTIONS AND HAVE 30 MINUTES REMAINING. 1-26. A patient presents to the physician’s office to ask questions about color blindness. The patient is color-blind, as is one of his brothers. His maternal grandfather was color-blind, but his mother, father, daughter, and another brother are not. His daughter is now pregnant. The risk that her child will be color-blind is a. b. c. d. e. 100% 50% 25% 12.5% Virtually 0 1-27. A 55-year-old female given a general anesthetic for a surgical procedure develops hyperthermia, hypertension, hyperkalemia, tachycardia, muscle rigidity, and metabolic acidosis. Which of the following general anesthetics did she receive? a. b. c. d. e. Ketamine Midazolam Thiopental Propofol Halothane
  • Block 1 Questions 15 1-28. A 30-year-old female stored her contact lenses in tap water. She noticed deterioration of vision and visited an ophthalmologist who diagnosed her with severe retinitis. Culture of the water as well as vitreous fluid would most likely reveal a. b. c. d. e. Naegleria Pneumocystis Acanthamoeba Babesia Entamoeba coli 1-29. A 25-year-old male reports to his physician that he has not been able to sleep for over two days and has been having “strange reactions.” These reactions are most apt to be caused by a. b. c. d. e. Increased levels of blood cortisol Physiologic stress in response to sleep deprivation The effects of the rebound phenomenon Perceptual distortions Feelings of excessive tiredness 1-30. A 45-year-old male is hospitalized for treatment of myocardial infarction. His father and a paternal uncle also had heart attacks at an early age. His cholesterol is elevated, and lipoprotein electrophoresis demonstrates an abnormally high ratio of low- to high-density lipoproteins (LDL to HDL). Which of the following is the most likely explanation for this problem? a. b. c. d. e. Mutant HDL is not responding to high cholesterol levels Mutant LDL is not responding to high cholesterol levels Mutant caveolae proteins are not responding to high cholesterol levels Mutant LDL receptors are deficient in cholesterol uptake Intracellular cholesterol is increasing the number of LDL receptors 1-31. A 3-year-old child presents at the physician’s office with symptoms of coryza, conjunctivitis, low-grade fever, and Koplik’s spots. The causative agent of this disease belongs to which group of viruses? a. b. c. d. e. Adenovirus Herpesvirus Picornavirus Orthomyxovirus Paramyxovirus
  • 16 Clinical Vignettes for the USMLE Step 1 1-32. A 25-year-old female suspected of having vitamin D–resistant rickets has decreased blood phosphate levels. Aside from high-dose vitamin D and oral phosphate, an alternative therapeutic approach might be the use of which of the following? a. b. c. d. e. Estrogen Pamidronate Hydrochlorothiazide Prednisone Calcitrol 1-33. A 52-year-old female presents with nausea, fatigue, muscle weakness, and intermittent pain in her left flank. Laboratory examination reveals an increased serum calcium and a decreased serum phosphorus. The patient’s plasma parathyroid hormone levels are increased, but parathyroid hormone–related peptide levels are within normal limits. Urinary calcium is increased, and microhematuria is present. The patient’s abnormality is most likely caused by a. b. c. d. e. Primary hyperparathyroidism Primary hypoparathyroidism Pseudohypoparathyroidism Secondary hyperparathyroidism Secondary hypoparathyroidism
  • Block 1 Questions 17 1-34. The accompanying x-ray shows the shoulder of an 11-year-old female who fell off the monkey bars, extending her arm in an attempt to break her fall. The small arrows indicate a fracture in the area of the surgical neck of the humerus. The large arrows indicate a. b. c. d. e. A fracture at the anatomic neck of the humerus The glenohumeral joint The joint space between the proximal humerus and the acromion of the scapula The proximal humeral epiphyseal plate What is commonly called a shoulder separation
  • 18 Clinical Vignettes for the USMLE Step 1 1-35. A newborn begins vomiting after feeding, becomes severely jaundiced, and has liver disease. Treatment for possible sepsis is initiated, and the urine is found to have reducing substances. A blood screen for galactosemia is positive, and lactose-containing substances are removed from the diet. Lactose is toxic in this case because a. b. c. d. e. Excess glucose accumulates in the blood Galactose is converted to the toxic substance galactitol (dulcitol) Galactose competes for glucose during hepatic glycogen synthesis Galactose is itself toxic in even small amounts Glucose metabolism is shut down by excess galactose 1-36. A 36-year-old male with a bipolar disorder is treated with lithium. Among the following adverse effects, which is associated with lithium treatment? a. b. c. d. e. Browning of the vision Hypothyroidism Agranulocytosis Neuroleptic malignant syndrome Pseudodepression 1-37. A 24-year-old female presents with severe pain during menses (dysmenorrhea). To treat her symptoms, you advise her to take indomethacin in the hopes that it will reduce her pain by interfering with the production of a. b. c. d. e. Bradykinin Histamine Leukotrienes Phospholipase A2 Prostaglandin F2
  • Block 1 Questions 19 1-38. A pathologist views the following tissues (A and B) in a biopsy. She determines that the tissues are normal. The presence of both of these tissues indicates that the sample was taken from the region of the junction between the a. b. c. d. e. Anal canal and rectum Esophagus and stomach Skin of the face and mucous epithelium of the lip Stomach and duodenum Vagina and cervix
  • 20 Clinical Vignettes for the USMLE Step 1 1-39. A child develops chronic diarrhea and liver inflammation in early infancy when the mother begins using formula that includes corn syrup. Evaluation of the child demonstrates sensitivity to fructose in the diet. Which of the following glycosides contains fructose and therefore should be avoided when feeding or treating this infant? a. b. c. d. e. Sucrose Oaubain Lactose Maltose Streptomycin 1-40. A 49-year-old man who smokes two packs of cigarettes a day presents with a lung mass on x-ray and recent weight gain. Laboratory examination shows hyponatremia with hyperosmolar urine. The patient probably has a. b. c. d. e. Renal failure Pituitary failure Conn’s syndrome Cardiac failure Inappropriate ADH 1-41. A college student takes part in a sleep laboratory experiment in which he is awakened repeatedly when his electroencephalogram (EEG) indicates that he has entered rapid-eye-movement (REM) sleep. This disruption of normal sleep is most likely to produce a. b. c. d. e. A rebound phenomenon of increased dreaming An increase in anxiety and irritability Acceleration of memory formation of emotionally toned words A decrement in intellectual function A temporary increase in nightmares 1-42. A 33-year-old female patient treated with haloperidol for a history of schizophrenia is seen in the ED because of complaints of fever, stiffness, and tremor. Her temperature is 104°F and her serum creatine kinase (CK) , level is elevated. What has occurred? a. b. c. d. e. Overdose Allergy Neuroleptic malignant syndrome (NMS) Tardive Dyskinesia Parkinsonism
  • Block 1 Questions 21 1-43. A teenage girl presents in the emergency room with paroxysms of dyspnea, cough, and wheezing. Her parents indicate that she has had these “attacks” during the past winter, and that they have worsened and become more frequent during the spring allergy season. Which of the following cell types is correctly matched to a function it may perform in this patient’s disease? a. b. c. d. e. Alveolar macrophages, enhanced mucociliary transport Plasma cells, bronchoconstriction Eosinophils, bronchodilation Goblet cells, hyposecretion Mast cells, edema 1-44. A young man with hypercholesterolemia is rushed to the hospital with crushing chest pain radiating to his left arm and a probable heart attack. Which of the following treatments should be considered? a. b. c. d. e. A platelet transfusion Heparin infusion Thrombin infusion Fibrinogen infusion Tissue plasminogen activator infusion 1-45. A patient becomes markedly tetanic following a recent thyroidectomy. This symptom can be rapidly reversed by the administration of a. b. c. d. e. Vitamin D Calcitonin PTH Plicamycin (mithramycin) Calcium gluconate (CaG) 1-46. A 26-year-old woman has been amenorrheic for 2.5 months. Your first choice for diagnostic evaluation is a. b. c. d. e. hCG LH Estradiol Prolactin Progesterone
  • 22 Clinical Vignettes for the USMLE Step 1 1-47. A 45-year-old man was riding a snowmobile and hit a snow-covered rocky outcropping. While recovering from the accident, he slipped and fell on the outcropping and now is experiencing pain in the gluteal region. In this CT scan, the dark linear structure indicated by the arrow is a. b. c. d. e. A fracture of the ilium The sacroiliac joint A spinal nerve The superior gluteal artery The inferior gluteal artery
  • Block 1 Questions 23 1-48. A 36-year-old male heroin addict is seen in the ED because he cannot be aroused from sleep. On examination, he has shallow breathing and pinpoint pupils. Naloxone is administered, and the patient wakes up. Which of the opiate receptor subtypes that binds naloxone is responsible for reversing the respiratory depression and miosis? a. δ b. κ c. µ 1-49. A 49-year-old female presents with signs of anemia and states that every morning her urine is dark. Workup reveals that her red blood cells lyse in vitro with acid (positive Ham’s test). What is the best diagnosis for this patient? a. b. c. d. e. Warm autoimmune hemolytic anemia Paroxysmal nocturnal hemoglobinuria Paroxysmal cold hemoglobinuria Isoimmune hemolytic anemia Cold-agglutinin autoimmune hemolytic anemia 1-50. A 34-year-old man has been diagnosed with chronic paranoid schizophrenia for 10 years. He is currently in a psychiatric hospital and is not on psychotropic medications. More than 50% of individuals with this diagnosis and off medications would have abnormalities in which of these tests? a. b. c. d. e. Lactate infusion test Dexamethasone suppression test Eye pursuit test Thyrotropic releasing hormone (TRH) stimulation test Prolactin stimulation test
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  • BLOCK 2 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • BLOCK 2 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Questions 2-1. A patient with reduced VC, FRC, and RV is found to have a normal pH. A tentative diagnosis of diffuse interstitial fibrosis is made. Which of the following characteristics are consistent with this disease? a. b. c. d. e. An increase in lung compliance A decrease in respiratory rate An increase in the V/Q ratio A decrease in PaCO2 An increase in the FEV1/FVC ratio 2-2. A 45-year-man has decreased libido and decreased sexual function. A large pituitary tumor is found. His prolactin is 20 (less than 15). Testing of his pituitary-gonadal axis most likely will show a. b. c. d. e. Normal testosterone and low LH High testosterone and normal LH Low testosterone and low LH Normal testosterone and normal LH Low testosterone and high LH 27
  • 28 Clinical Vignettes for the USMLE Step 1 2-3. A 45-year-old male with a history of colonic diverticulosis complains of fever with pain and swelling in the rectal area. You are concerned that the colonic diverticulum may have become infected (diverticulitis) and ruptured into the space indicated by the * in this CT scan. Which of the following is correct regarding the indicated space? a. b. c. d. It is called the paracolic gutter The space is largely filled with muscle The space is located superior to the pelvic diaphragm Pus from the abscessed diverticuli in that space can extend anteriorly to the perineal body, inferior to the urogenital diaphragm e. Pus from the abscessed diverticuli in that space can extend superiorly anterior to the sacrum
  • Block 2 Questions 29 2-4. A jaundiced one-day-old premature infant with an elevated free bilirubin is seen in the premature-baby nursery. The mother received an antibiotic combination preparation containing sulfamethizole for a urinary tract infection (UTI) one week before delivery. You suspect that the infant’s findings are caused by the sulfonamide because of the following mechanism: a. b. c. d. Enhanced synthesis of bilirubin Competition between the sulfonamide and bilirubin for binding sites on albumin Inhibition of bilirubin degradation Inhibition of urinary excretion of bilirubin 2-5. A 35-year-old woman who underwent a modified radical mastectomy of her right breast for infiltrating ductal carcinoma 2 years ago presents with enlargement of her right breast. The breast has a swollen, reddiscolored appearance. It is diffusely indurated and tender on palpation. Multiple axillary lymph nodes are palpable in the lower axilla. The working clinical diagnosis is inflammatory carcinoma. Microscopic sections from this red, indurated area are most likely to reveal a. b. c. d. e. Duct ectasia with numerous plasma cells Extensive invasion of dermal lymphatics Infiltrating malignant ducts surrounded by numerous neutrophils Malignant vascular tumor forming slitlike spaces Marked dermal desmoplasia 2-6. A man drinks 2 L of water to replenish the fluids lost by sweating during a period of exercise. Compared with the situation prior to the period of sweating, a. b. c. d. e. His intracellular fluid will be hypertonic His extracellular fluid will be hypertonic His intracellular fluid volume will be greater His extracellular fluid volume will be greater His intracellular and extracellular fluid volumes will be unchanged
  • 30 Clinical Vignettes for the USMLE Step 1 2-7. A 75-year-old male, postprostatectomy for carcinoma of the prostate with local metastasis found during surgery, would best be treated with which of the following? a. b. c. d. e. Mifepristone Spironolactone Aminoglutethimide Leuprolide Fludrocortisone 2-8. A nurse develops clinical symptoms consistent with hepatitis. She recalls sticking herself with a needle approximately 4 months before after drawing blood from a patient. Serologic tests for HBsAg, antibodies to HBsAg, and hepatitis A virus (HAV) are all negative; however, she is positive for IgM core antibody. The nurse a. b. c. d. Does not have hepatitis B Has hepatitis A Is in the late stages of hepatitis B infection Is in the “window” (after the disappearance of HBsAg and before the appearance of anti-HBsAg) e. Has hepatitis C 2-9. A 22-year-old male with a five-year history of bronchial asthma has developed increased frequency and severity of acute asthmatic attacks. A low dose of which inhaled steroid could be added to his treatment regimen? a. b. c. d. e. Prednisolone Amcinonide Beclomethasone Cortisone Fluocinolone 2-10. A patient has muscular weakness. His parents and sister do not have weakness, but his mother’s brother has weakness. You suspect Duchenne’s muscular dystrophy. This is an example of a. b. c. d. Autosomal recessive inheritance X-linked recessive inheritance Semidominant inheritance Autosomal dominant inheritance
  • Block 2 Questions 31 2-11. An elderly patient who becomes acutely short of breath presents with the combination of hypotension, elevated jugular venous pressure, and muffled heart sounds. This triad of symptoms is most suggestive of a. b. c. d. e. Chronic pericarditis Chronic pericardial effusion Cardiac tamponade Dissecting aortic aneurysm Right heart failure 2-12. A patient presents with keratoconjunctivitis. The differential diagnosis should include infection with which of the following viruses? a. b. c. d. e. Parvovirus Adenovirus Epstein-Barr virus Respiratory syncytial virus Varicella-zoster virus 2-13. A 2-year-old infant is brought to the emergency room with hemolytic uremic syndrome and thrombocytopenia. Which one of the following bacteria would most likely be isolated from a stool specimen? a. b. c. d. e. Shigella Salmonella Aeromonas E. coli 0157/H7 Enterobacter 2-14. Following surgery involving the lateral wall of the pelvis, a patient reported anesthesia over the medial thigh. Subsequent examination revealed weakened adduction of the thigh. Which nerve was most likely injured during the pelvic surgery? a. b. c. d. e. Pudendal nerve Genitofemoral nerve Superior gluteal nerve Femoral nerve Obturator nerve
  • 32 Clinical Vignettes for the USMLE Step 1 2-15. You have been asked to consult regarding stress in the workplace in a busy factory. One group of workers have jobs that are self-paced. A second group have jobs that are machine-paced and therefore largely out of the workers’ control. The workers who do not control their pace of work would be differentiated from the other group in physiologic response by a much greater release of a. b. c. d. e. Catecholamines Thyroid hormone Serotonin Prostaglandins γ-Aminobutyric acid (GABA) 2-16. An AIDS patient complains of headaches and disorientation. A clinical diagnosis of Toxoplasma encephalitis is made and Toxoplasma cysts were observed in a brain section (see figure below). Which one of the following antibody results would be most likely in this patient? a. b. c. d. e. IgM nonreactive, IgG nonreactive IgM nonreactive, IgG reactive (low titer) IgM reactive (low titer), IgG reactive (high titer) IgM reactive (high titer), IgG reactive (high titer) IgM reactive (high titer), IgG nonreactive
  • Block 2 Questions 33 2-17. A 72-year-old woman with emphysema presents to the emergency room with fatigue and respiratory distress. Which set of arterial blood gas values below would represent her condition and reflect a shift of the hemoglobin oxygen dissociation curve to the right? a. b. c. d. e. pH 7.05, bicarbonate 15 mM, PCO2 60, PO2 88 pH 7.15, bicarbonate 10 mM, PCO2 30, PO2 88 pH 7.25, bicarbonate 15 mM, PCO2 30, PO2 88 pH 7.40, bicarbonate 24 mM, PCO2 60, PO2 88 pH 7.45, bicarbonate 15 mM, PCO2 60, PO2 88 2-18. At the time of autopsy of a 39-year-old female who died of complications of systemic lupus erythematosus, several medium-sized vegetations are found on both sides of the mitral valve and tricuspid valve. These cardiac vegetations are most likely the result of a. b. c. d. e. Turbulent blood flow through an incompetent mitral valve Abnormal secretion of a vasoactive amine Presence of an anticardiolipin antibody Cachexia produced by a hypercoagulable state Bacterial colonization of an abnormal valve 2-19. A 25-year-old male is seen in the emergency department (ED). He is disoriented but states that he has had nausea, vomiting, abdominal pain, and diarrhea since he took “too many pain pills.” Before he can tell you more, he loses consciousness. Liver function tests are abnormal. In addition to gastric lavage, what is the appropriate treatment? a. b. c. d. e. Naloxone Diphenoxylate N-acetyl-L-cysteine Prochlorperazine Pralidoxime
  • 34 Clinical Vignettes for the USMLE Step 1 2-20. A comatose laboratory technician is rushed into the emergency room. She dies while you are examining her. Her most dramatic symptom is that her body is literally hot to your touch, indicating an extremely high fever. You learn that her lab has been working on metabolic inhibitors and that there is a high likelihood that she accidentally ingested one. Which one of the following is the most likely culprit? a. b. c. d. e. Barbiturates Piericidin A Dimercaprol Dinitrophenol Cyanide 2-21. A 52-year-old male patient, who has smoked two packs of cigarettes per day for the past 38 years, presents with diminished breath sounds detected by auscultation accompanied by faint high-pitched rhonchi at the end of each expiration and a hyperresonant percussion note. In addition, he shows discomfort during breathing and is using extra effort to involve accessory muscles to lift the sternum. The diminished lung sounds in this patient are primarily due to which cellular events? a. Monocytic infiltration leading to collagenase destruction of bronchiolar connective tissue support b. Neutrophilic infiltration leading to destruction of bronchiolar and septal elastic fibers c. Monocytic infiltration leading to breakdown of the bronchiolar smooth muscle d. Neutrophilic infiltration leading to excess production of antiprotease activity in the lung parenchyma e. Monocytic infiltration leading to excess production of antiprotease activity in the lung parenchyma 2-22. Parents of a child with attention deficit hyperactivity disorder (ADHD) consult with you to inquire about the heritability of the disorder. The husband had attention span and learning problems in secondary school. One of his brothers did also, and an uncle may have had learning problems. You response would include the fact that ADHD has a heritability of approximately a. b. c. d. e. 70% 60% 50% 40% 30%
  • Block 2 Questions 35 2-23. A 4-year-old male with mental retardation, self-mutilation, and hyperuricemia is likely to have a deficiency of an enzyme involved in the a. b. c. d. e. Conversion of homogentisic acid to methylacetoacetate Degradation of galactocerebroside Breakdown of branched-chain amino acids Recycling of guanine and hypoxanthine Synthesis of UMP and CTP 2-24. A teenage girl is brought to the medical center because of her complaints that she gets too tired when asked to participate in gym class. A consulting neurologist finds muscle weakness in the girl’s arms and legs. When no obvious diagnosis can be made, biopsies of her muscles are taken for tests. Chemistries reveal greatly elevated amounts of triacylglycerides esterified with primarily long-chain fatty acids. Pathology reports the presence of significant numbers of lipid vacuoles in the muscle biopsy. Which one of the following is the most likely diagnosis? a. b. c. d. e. Fatty acid synthase deficiency Tay-Sachs disease Carnitine deficiency Biotin deficiency Lipoprotein lipase deficiency 2-25. A person who had recently consumed half a box of raspberries came down with severe watery diarrhea. Surprisingly, the patient felt tired for a few days and had a low-grade fever. The most likely cause of infection is a. b. c. d. e. Cryptosporidium Escherichia coli 0157:H7 Isospora Vibrio Cyclospora
  • 36 Clinical Vignettes for the USMLE Step 1 YOU SHOULD HAVE COMPLETED APPROXIMATELY 25 QUESTIONS AND HAVE 30 MINUTES REMAINING. 2-26. A 50-year-old male is seen in the emergency department (ED) with a blood pressure of 260/160 mmHg. Blurring optic discs with indistinct margins are seen on ophthalmologic examination. An intravenous drip of sodium nitroprusside is administered. What is the mechanism of action of sodium nitroprusside? a. b. c. d. e. f. g. h. i. α-adrenergic receptor agonist α-adrenergic receptor antagonist β-adrenergic receptor agonist β-adrenergic receptor antagonist Ganglionic blocking agent Depletion of nerve terminal storage of NE Direct smooth-muscle vasodilator ACE antagonist Angiotensin receptor antagonist
  • Block 2 Questions 37 2-27. A 19-year-old male presents with a rash that involves a large, irregular portion of his trunk. Examination reveals several annular lesions that have a raised papulovesicular border with central hypopigmentation. Examination of this area under a Wood’s lamp reveals a yellow fluorescence. A scraping of this area viewed under the microscope after KOH is added reveals characteristic “spaghetti and meatball” forms. What is the cause of this skin lesion? a. b. c. d. e. Malassezia furfur Molluscum contagiosum Sarcoptes scabiei Staphylococcus aureus Trichophyton rubrum 2-28. A child with a large head, multiple fractures, and blue scleras (whites of the eyes) is evaluated for osteogenesis imperfecta (166200). One study involves labeling of collagen chains in tissue culture to assess their mobility by gel electrophoresis. Amino acids labeled with radioactive carbon 14 are added to the culture dishes in order to label the collagen. Which of the following amino acids would not result in labeled collagen? a. b. c. d. e. Serine Glycine Aspartate Glutamate Hydroxylserine 2-29. A physician examines a patient who complains of pain and paresthesia in the left leg. The distribution of the pain—running down the medial aspect of the leg and the medial side of the foot and including the great toe—is suggestive of a herniated intervertebral disk. The physician links the distribution of symptoms with nerve L4 and concludes that herniation has occurred at which location? a. b. c. d. e. L3–L4 intervertebral disk L4–L5 intervertebral disk L5–S1 intervertebral disk S1–S2 intervertebral disk Insufficient data to determine
  • 38 Clinical Vignettes for the USMLE Step 1 2-30. A former heroin addict is maintained on methadone, but succumbs to temptation and buys an opioid on the street. He takes it and rapidly goes into withdrawal. Which opioid did he take? a. b. c. d. e. Meperidine Heroin Pentazocine Codeine Propoxyphene 2-31. A 26-year-old female acutely develops lower abdominal pain and vaginal bleeding. While in the bathroom she passes a cast of tissue composed of clot material and then collapses. She is brought to the hospital, where a physical examination reveals a soft, tender mass in right adnexa and pouch of Douglas. Histologic examination of the tissue passed in the bathroom reveals blood clots and decidualized tissue. No chorionic villi or trophoblastic tissue are present. Which one of the following conditions is most likely present in this individual? a. b. c. d. e. Aborted intrauterine pregnancy Complete hydatidiform mole Ectopic pregnancy Endometrial hyperplasia Partial hydatidiform mole 2-32. A young woman had an initial episode of psychosis at age 19, with paranoid delusions, auditory hallucinations, and disorganized behavior. She responded well to an atypical neuroleptic, but has not been able to live independently and develop an occupation. She has had two subsequent psychotic episodes similar to the initial one. The etiology of her chronic psychiatric illness is most strongly related to a. b. c. d. e. Environmental factors Polygenic inheritance A chromosomal abnormality Simple recessive inheritance An inborn error of metabolism
  • Block 2 Questions 39 2-33. Following childbirth, a woman experienced urinary incontinence, particularly when coughing. This was most likely caused by tearing of the a. b. c. d. e. Puborectalis muscle Obturator internus muscle Pubococcygeus muscle Superficial transverse perineus muscle Piriformis muscle 2-34. A 22-year-old man comes to the emergency room of your hospital because he has a diffuse, erythematous rash involving nearly all of his body. His total WBC count is greater than 100,000 cells/mm3. He also complains of bone pain, severe irritability, weakness, fatigue, nausea and vomiting, constipation, photophobia, and polyuria. His electrocardiogram (ECG) shows shortening of the QT interval, prolongation of the PR interval, and nonspecific T wave changes. The most likely cause of his symptoms is a. b. c. d. Hypercalcemia Hypocalcemia Hypophosphatemia Hyperkalemia
  • 40 Clinical Vignettes for the USMLE Step 1 2-35. An adolescent presents with shortness of breath during exercise and is found to be anemic. A hemoglobin electrophoresis is performed that is depicted in the figure below. The adolescent’s sample is run with controls including normal, sickle trait, and sickle cell anemia, and serum. The adolescent is determined to have an unknown hemoglobinopathy. Which one of the lanes contains the adolescent’s sample? a. b. c. d. e. Lane A Lane B Lane C Lane D Lane E 2-36. A 30-year-old pregnant female develops a UTI that is caused by Chlamydia trachomatis. Of the following, which is the best agent to use in this patient? a. b. c. d. e. Tetracycline Levofloxacin Gentamycin Erythromycin Sulfamethoxazole-trimethoprim
  • Block 2 Questions 41 2-37. A patient takes excessive amounts of bicarbonates to treat his heartburn. Which one of the following blood-gas values will be observed in this patient? a. b. c. d. e. PaCO2 (mM) 25 35 45 55 65 pH 7.7 7.6 7.5 7.4 7.3 2-38. A 25-year-old female presents with lower abdominal pain, fever, and a vaginal discharge. Pelvic examination reveals bilateral adnexal (ovarian) tenderness and pain when the cervix is manipulated. Cultures taken from the vaginal discharge grow Neisseria gonorrhoeae. What is your diagnosis of the cause of this patient’s adnexal pain? a. b. c. d. e. Adenomatoid tumor Ectopic pregnancy Endometriosis Luteoma of pregnancy Pelvic inflammatory disease 2-39. A newborn female has a large and distorted cranium, short and deformed limbs, and very blue scleras (whites of the eyes). Radiographs demonstrate multiple limb fractures and suggest a diagnosis of osteogenesis imperfecta (brittle bone disease). Analysis of type I collagen protein, a triple helix formed from two α1 and one α2 collagen chains, shows a 50% reduction in the amount of type I collagen in the baby’s skin. DNA analysis demonstrates the presence of two normal α1 alleles and one normal α2 allele. These results are best explained by Deficiency of α1 collagen peptide synthesis Inability of α1 chains to incorporate into triple helix Defective α1 chains that interrupt triple helix formation Incorporation of defective α2 chains that cause instability and degradation of the triple helix e. A missense mutation that alters the synthesis of α1 chains a. b. c. d.
  • 42 Clinical Vignettes for the USMLE Step 1 2-40. A child has mononucleosis-like symptoms yet the test for mononucleosis and the EBV titers are negative. One of the causes of heterophilenegative mononucleosis is a. b. c. d. e. Cytomegalovirus Herpes simplex virus Varicella-zoster virus Adenovirus Coxsackievirus 2-41. A 43-year-old woman who has suffered from diabetes for 30 years comes into the clinic. She is anemic with a hematocrit of 22. Which of the following would most likely explain her condition? a. Decreased hepatic production of erythropoietin, leading to decreased numbers of circulating reticulocytes in the bloodstream b. Increased erythropoietin production by the liver, resulting in increased numbers of reticulocytes c. Decreased renal erythropoietin production, leading to reduced numbers of red blood cells d. Decreased estrogen levels, stimulating hepatic production of erythropoietin e. Decreased estrogen levels, inhibiting renal production of erythropoietin 2-42. A 15-year-old male attempts suicide with a liquid that causes intense abdominal pain, skeletal muscle cramps, projectile vomiting, severe diarrhea, and difficulty swallowing. On examination, he is found to be volume depleted and is showing signs of alteration of consciousness. Which of the following may account for these symptoms? a. b. c. d. e. Arsenic (As) Cadmium (Cd) Iron (Fe) Lead (Pb) Zinc (Zn) 2-43. A patient has arthralgia, a rash, lymphadenopathy, pneumonia but no fever. Which of the following diseases is most likely based on these symptoms? a. b. c. d. e. Dengue fever St. Louis encephalitis Infectious mononucleosis Hepatitis HIV infection
  • Block 2 Questions 43 2-44. The blood pressure of a 65-year-old male is well controlled by a Ca2+ channel blocker that is used to treat his essential hypertension. When placed on cimetidine to control symptoms related to gastroesophageal reflux disease (GERD), he has episodes of dizziness. How does cimetidine’s effect on Ca2+ channel blockers account for the dizziness? a. b. c. d. e. It increases their rate of intestinal absorption It decreases their plasma protein binding It decreases their volume of distribution It decreases their metabolism by cytochrome P450 It decreases their tubular renal secretion 2-45. An infant smiles every time the parents approach the crib and look at him. Emotional expressions in an infant, such as smiling, are stereotyped sequences of movements that are under the control of a. b. c. d. e. A specific sign stimulus Genetic influences A conditioned response Imprinting Cultural determinants 2-46. A 39-year-old female presents with increasing shortness of breath. She states that for the past 6 months she has been taking an unauthorized appetite suppressant to try to lose weight. Physical examination reveals signs of right heart failure. She is admitted to the hospital to work up her symptoms, but she dies suddenly. A section from her heart at the time of autopsy reveals marked thickening of the right ventricle, but the thickness of the left ventricle is within normal limits. The endocardium does not appear to be increased in thickness or fibrotic, and the cardiac valves do not appear abnormal. Neither ventricular cavity is dilated. Which one of the following best describes this cardiac pathology? a. b. c. d. e. Carcinoid heart disease Cor pulmonale Eccentric hypertrophy Systemic hypertensive heart disease Volume overload to the heart
  • 44 Clinical Vignettes for the USMLE Step 1 2-47. A 30-year-old man presents with weight gain, dorsocervical fat pad, and proximal muscle weakness. His urinary free cortisol is significantly elevated and does not suppress with dexamethasone. The plasma ACTH is undetectable. Your next best diagnostic test is a. b. c. d. e. Serum antidiuretic hormone (ADH) Chest CT MRI of the pituitary ACTH stimulation test Abdominal CT Questions 2-48 through 2-49 An elderly female patient complains that she cannot taste the food that she eats. A careful neurological examination reveals no evidence of peripheral damage of the taste receptors. The evidence suggests, instead, that there was selective damage of certain regions of the brainstem. 2-48. One of the sites where damage could result in the selective loss of taste includes the a. b. c. d. e. Superior olivary nucleus Inferior salivatory nucleus Solitary nucleus Spinal nucleus of the trigeminal nerve Reticular tegmental nucleus of the pons 2-49. A principal target of the brainstem structure (referring to the answer to the previous question) is the a. b. c. d. e. Anterior thalamic nucleus Reticular thalamic nucleus Ventral posteromedial thalamic nucleus Ventrolateral thalamic nucleus Dorsomedial thalamic nucleus
  • Block 2 Questions 45 2-50. A 46-year-old woman presents with a pain in the left leg that worsens on weight-bearing. An x-ray shows demineralization and a decalcified (EDTA-treated) biopsy shows reduction in bone quantity. The patient had undergone menopause at age 45 without estrogen replacement. She reports long-standing diarrhea. In addition, laboratory tests show low levels of 25hydroxyvitamin D, calcium, and phosphorus and elevated alkaline phosphatase. A second bone biopsy, which was not decalcified, shows uncalcified osteoid on all the bone surfaces. On the basis of these data, the most likely diagnosis would be a. b. c. d. e. Osteoporosis Osteomalacia Scurvy Paget’s disease Hypoparathyroidism
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  • BLOCK 3 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • BLOCK 3 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Questions 3-1. A 52-year-old white woman with breast cancer receiving adjuvant therapy presents with back pain that intensifies on movement and pain over the L1 vertebral body when she coughs and that radiates down her left lower extremity to her leg and foot. The most likely etiology of this disorder is a. b. c. d. Paraneoplastic disorder Trauma to the lumbar disk Muscular spasm of the intercostal muscles Possible spinal cord compression 3-2. An obese 18-year-old male patient presents with small, firm testes, a small penis, little axillary and and facial hair, azoospermia, gynecomastia, and elevated levels of plasma gonadotropins. He has had difficulty in social adjustment throughout high school, but this has worsened and he has been referred for genetic and endocrine screening. The karyotype from periphBarr bodies? eral blood leukocytes would most likely show a. b. c. d. e. No One Two Three Four 49
  • 50 Clinical Vignettes for the USMLE Step 1 3-3. A nine-year-old boy is diagnosed with acute lymphoblastic leukemia. He is maintained on methotrexate. A recent platelet count is below normal, and a stool guaiac is 4+. Which of the following agents should be administered to counteract methotrexate toxicity? a. b. c. d. e. N-acetyl-L-cysteine Vitamin K Penicillamine Leucovorin Deferoxamine 3-4. An individual has difficulty in adjusting his head, especially after he changes his posture. The most likely pathway affected that might cause this deficit is the a. b. c. d. e. Lateral vestibulospinal tract Medial vestibulospinal tract Medial reticulospinal tract Lateral reticulospinal tract Rubrospinal tract 3-5. A 27-year-old female has just returned from a trip to Southeast Asia. In the past 24 hours, she has developed shaking, chills, and a temperature of 104°F A blood smear reveals Plasmodium vivax. Which of the following . agents should be used to eradicate the extraerythrocytic phase of the organism? a. b. c. d. e. Primaquine Pyrimethamine Quinacrine Chloroquine Chloroguanide 3-6. During a viral infection, a 23-year-old female develops enlarged lymph nodes at multiple sites (lymphadenopathy). A biopsy from one of these enlarged lymph nodes reveals a proliferation of reactive T immunoblasts, cells that have prominent nucleoli. These reactive T cells are most likely to be found in which one of the following regions of the lymph node? a. b. c. d. e. Hilum Medullary sinuses Paracortex Primary follicles Secondary follicles
  • Block 3 Questions 51 3-7. An immunocompromised person with history of seizures had an MRI that revealed a temporal lobe lesion. Brain biopsy results showed multinucleated giant cells with intranuclear inclusions. The most probable cause of the lesion is a. b. c. d. e. Hepatitis C virus Herpes simplex virus Listeria monocytogenes Coxsackievirus Parvovirus 3-8. A 55-year-old woman presents with pain in her right hip and thigh. The pain started approximately six months ago and is a deep ache that worsens when she stands or walks. Your examination reveals increased warmth over the right thigh. The only laboratory abnormalities are alkaline phosphatase 656 IU/L (normal 23 to 110 IU/L), elevated 24-h urine hydroxyproline, and osteocalcin 13 ng/mL (normal 6 ng/mL). X-ray of hips and pelvis shows osteolytic lesions and regions with excessive osteoblastic activity. Bone scan shows significant uptake in the right proximal femur. Which of the following would you include in your differential diagnosis? a. b. c. d. e. Paget’s disease Multiple myeloma Osteomalacia Osteoporosis Hypoparathyroidism
  • 52 Clinical Vignettes for the USMLE Step 1 3-9. Allen is a 30-year-old bachelor who frequents singles bars. He is cautious and always uses a condom in his sexual encounters. Recently, he has felt “off,” experiencing a sore throat, malaise, and a slight fever. When you see him in your office, he has a few swollen lymph nodes and has a large palpable structure in the left upper abdomen indicated by the * in the accompanying radiograph. He had a positive monospot test and an elevated sedimentary rate. Your diagnosis is infectious mononucleosis. The structure you palpated was a. b. c. d. e. An enlarged liver (hepatomegaly) An enlarged spleen (splenomegaly) The stomach A tumor of the liver Liver cirrhosis
  • Block 3 Questions 53 3-10. A woman tests positive for pregnancy. In order for the pregnancy to proceed uneventfully, which of the following must occur? a. b. c. d. e. The corpus luteum must secrete progesterone to sustain the endometrium The pituitary must secrete hCG to maintain the corpus luteum The pituitary must secrete prolactin to sustain the placenta The placenta must secrete FSH to maintain ovarian function The placenta must secrete LH to maintain ovarian function 3-11. A 4-year-old boy presents with a history of numerous fractures that are not related to excessive trauma. Physical examination reveals evidence of previous fractures along with abnormally loose joints, decreased hearing, and blue scleras. X-rays of the boy’s arms reveal the bones to be markedly thinned. What is the correct diagnosis? a. b. c. d. e. Osteopetrosis Osteoporosis Osteomalacia Osteogenesis imperfecta Osteitis deformans 3-12. A 17-year-old girl presents with cervical lymphadenopathy, fever, and pharyngitis. Infectious mononucleosis is suspected. The most rapid and clinically useful test to make this diagnosis is a. b. c. d. e. IgM antibody to viral core antigen (VCA) IgG antibody to VCA Antibody to Epstein-Barr nuclear antigen (EBNA) Culture C reactive protein (CRP) 3-13. A 76-year-old female with an eight-year history of CHF that has been well controlled with digoxin and furosemide develops recurrence of dyspnea on exertion. On physical examination, she has sinus tachycardia, rales at the base of both lungs, and 4+ pitting edema of the lower extremities. Which agent could be added to her therapeutic regimen? a. b. c. d. e. Dobutamine Hydralazine Minoxidil Prazosin Enalapril
  • 54 Clinical Vignettes for the USMLE Step 1 3-14. A 30-year-old woman undergoes surgery for a very large, but fortunately benign, brain tumor. For 2 days after the surgery she is unable to perform certain previously learned motor functions. This disorder is called a. b. c. d. e. Apraxia Aphasia Abulia Anomia Alexia 3-15. A 50-year-old man asks for help in establishing an effective weight loss program. He has been 40 lbs overweight for several years. In planning a weight loss intervention, the most effective self-management procedure is a. b. c. d. e. Information control Self-monitoring Self-punishment Self-reward Enlisting social support 3-16. A patient presents in her fifth pregnancy with a history of numbness and tingling in her right thumb and index finger during each of her previous four pregnancies. Currently, the same symptoms are constant, although generally worse in the early morning. Symptoms could be somewhat relieved by vigorous shaking of the wrist. Neurologic examination revealed atrophy and weakness of the abductor pollicis brevis, the opponens pollicis, and the first two lumbrical muscles. Sensation was decreased over the lateral palm and the volar aspect of the first three digits. Numbness and tingling were markedly increased over the first three digits and the lateral palm when the wrist was held in flexion for 30 s. The symptoms suggest damage to a. b. c. d. e. The radial artery The median nerve The ulnar nerve Proper digital nerves The radial nerve
  • Block 3 Questions 55 3-17. A 3-year-old female ingests a bottle of aspirin by accident. Among the therapeutic interventions, which of the following should be included? a. b. c. d. e. Dimercaprol Deferoxamine Penicillamine Na2EDTA Activated charcoal 3-18. A 45-year-old woman veterinarian who is a faculty member at the nearby veterinary school comes to your office with complaints of a flulike syndrome of 9 days’ duration including persistent fever for all 9 days, extreme fatigue, and severe headache. She has a dry cough, an increased white count, and thrombocytopenia. Which one of the following is the likely cause of her infection? a. b. c. d. e. Influenzavirus Mycoplasma pneumoniae Chlamydia psittaci Coxiella burnetii Chlamydia pneumoniae 3-19. A 30-year-old man with recently developed AIDS is referred to you, as a primary care physician. What is apt to be the most prominent psychosocial factor or reaction that you can expect from him and perhaps help prevent? a. b. c. d. e. Loss of independence Fear of losing confidentiality Guilt Depressed mood Suicidal thoughts 3-20. A patient complains that he cannot move his right eye to the right and that the right side of his face is expressionless. The likely locus of the lesion is the a. b. c. d. e. Dorsal aspect of the medulla Ventromedial medulla Dorsal pons Ventromedial pons Medial midbrain
  • 56 Clinical Vignettes for the USMLE Step 1 3-21. A young boy is being evaluated for developmental delay, mild autism, and mental retardation. Physical examination reveals the boy to have large, everted ears and a long face with a large mandible. He is also found to have macroorchidism (large testes), and extensive workup reveals multiple tandem repeats of the nucleotide sequence CGG in his DNA. Which one of the following is the correct diagnosis for this patient? a. b. c. d. e. Fragile X syndrome Huntington’s chorea Myotonic dystrophy Spinal-bulbar muscular atrophy Ataxia-telangiectasia
  • Block 3 Questions 57 3-22. An AIDS patient presents to his primary care physician with a 2-week history of watery, nonbloody diarrhea. This stool revealed an organism which can be seen in the figure below. The most likely diagnosis is (Reproduced, with permission, from Garcia LS: Laboratory Methods for Diagnosis of Parasitic Infection. In Baron EJ and Finegold SM: Diagnostic Microbiology, 8/e, St. Louis, Mosby-Year Book: 1990.) a. b. c. d. e. Cyclospora Cryptosporidium Enterocytozoon Yeast Acid-fast bacilli
  • 58 Clinical Vignettes for the USMLE Step 1 3-23. A 55-year-old female with a blood pressure of 170/105 mmHg has pitting edema of the lower extremities and an elevated serum creatinine associated with a normal serum potassium. Which of the following agents is contraindicated in this patient? a. b. c. d. e. Triamterene Hydrochlorothiazide Metolazone Ethacrynic acid Acetazolamide 3-24. Several days following a myocardial infarction, a 51-year-old male develops the sudden onset of a new pansystolic murmur along with a diastolic flow murmur. Workup reveals increased left atrial pressure that develops late in systole and extends into diastole. These abnormalities in this individual are most likely the result of a. b. c. d. e. Aneurysmal dilation of the left ventricle Obstruction of the aortic valve Rupture of the left ventricle wall Rupture of a papillary muscle Thrombosis of the left atrial cavity 3-25. An adolescent female develops hemiballismus (repetitive throwing motions of the arms) after anesthesia for a routine operation. She is tall and lanky, and it is noted that she and her sister both had previous operations for dislocated lenses of the eyes. The symptoms are suspicious for the disease homocystinuria (236300). Which of the statements below is descriptive of this disease? a. b. c. d. e. Patients may be treated with dietary supplements of vitamin B12 Patients may be treated with dietary supplements of vitamin C There is deficient excretion of homocysteine There is increased excretion of cysteine There is a defect in the ability to form homocysteine from methionine by methylation
  • Block 3 Questions 59 YOU SHOULD HAVE COMPLETED APPROXIMATELY 25 QUESTIONS AND HAVE 30 MINUTES REMAINING. 3-26. A woman, recently returned from Africa, complains of having paroxysmal attacks of chills, fever, and sweating; these attacks last a day or two at a time and recur every 36 to 48 h. Examination of a stained blood specimen reveals ringlike and crescent-like forms within red blood cells. The infecting organism most likely is a. b. c. d. e. Plasmodium falciparum Plasmodium vivax Trypanosoma gambiense Wuchereria bancrofti Schistosoma mansoni
  • 60 Clinical Vignettes for the USMLE Step 1 3-27. An adult with mild, chronic anemia does not respond to iron supplementation. Blood is drawn and the red cell hemoglobin is analyzed. Which of the following results is most likely if the patient has an altered hemoglobin molecule (hemoglobinopathy)? a. Several proteins but only one red protein detected by high-performance liquid chromatography (HPLC) b. Two proteins detected in normal amounts by western blotting c. Several proteins and two red proteins separated by native gel electrophoresis d. Two labeled bands a slight distance apart after SDS-gel electrophoresis and reaction with labeled antibody to α- and β-globin e. A reddish mixture of proteins retained within a dialysis membrane 3-28. A medical student presents to the emergency room with a two-day history of severe vomiting and orthostatic hypotension. What kind of metabolic abnormalities would you expect? a. b. c. d. e. Hypokalemia, hypochloremia, and metabolic acidosis Hyperkalemia, hyperchloremia, and metabolic alkalosis Normal serum electrolytes and metabolic acidosis Normal serum electrolytes and metabolic alkalosis Hypokalemic, hypochloremic, metabolic alkalosis 3-29. Two parents are both affected with albinism (203100, 203200), but have a normal child. Which of the following terms best applies to this situation? a. b. c. d. e. Allelic heterogeneity Locus heterogeneity Variable expressivity Incomplete penetrance New mutation
  • Block 3 Questions 61 3-30. A 24-year-old female presents with a 2-year history of infertility. An endometrial biopsy is obtained approximately 5 to 6 days after the predicted time of ovulation. This biopsy specimen reveals secretory endometrium, but there is a significant difference (asynchrony) between the estimated chronologic menstrual date and the estimated histologic menstrual date. No proliferative endometrium is seen. Based on this information, what is the correct diagnosis for this biopsy specimen? a. b. c. d. Anovulatory cycle (no corpus luteum formed) Inadequate luteal phase (decreased functioning of the corpus luteum) Irregular shedding (prolonged functioning of the corpus luteum) Normal endometrium during the follicular phase of the cycle (no corpus luteum formed) e. Normal endometrium during the luteal phase of the cycle (normal corpus luteum) 3-31. During a visit to her gynecologist, a patient reports she received vitamin A treatment for her acne unknowingly during the first two months of an undetected pregnancy. Which organ systems in the developing fetus are most likely to be affected? a. b. c. d. e. The digestive system The endocrine organs The respiratory system The urinary and reproductive systems The skeletal and central nervous systems 3-32. A 32-year-old cancer patient, who has smoked two packs of cigarettes a day for 10 years, presents a decreased pulmonary function test. Physical examination and chest x-rays suggest preexisting pulmonary disease. Of the following drugs, which is best not prescribed? a. b. c. d. e. Vinblastine Doxorubicin Mithramycin Bleomycin Cisplatin
  • 62 Clinical Vignettes for the USMLE Step 1 3-33. In the operating room, a child receives succinylcholine as a muscle relaxant to facilitate intubation and anesthesia. The operation proceeds until it is time for recovery, when the child does not begin breathing. A hurried discussion with the father discloses no additional problems in the family, but he does say that he and his wife are first cousins. The most likely possibility is a. An autosomal dominant disorder that interferes with succinylcholine metabolism b. An autosomal recessive disorder that interferes with succinylcholine metabolism c. An X-linked disorder that interferes with succinylcholine metabolism d. A lethal gene transmitted through consanguinity that affects the respiratory system e. Mismanagement of halothane anesthesia during the operation 3-34. A 12-year-old boy is brought to your office by his mother because he developed a painless rash on his face and legs. The rash began as red papules and then became vesicular and pustular and finally it coalesced in honeycomb-like crusts. The boy does not have fever, but he does have several insect bites and he is unwashed and dressed in dirty clothes. This rash is likely to be a. b. c. d. e. Herpes simplex Shingles Impetigo Scarlet fever Erysipelas 3-35. A patient has all the gastrointestinal symptoms of infection with hepatitis A virus (HAV), yet all the tests for HAV-IgG and HAV-IgM are nonreactive. A possible cause of this infection is a. b. c. d. e. Hepatitis B surface antigen Hepatitis C Hepatitis D Hepatitis E Rotavirus
  • Block 3 Questions 63 3-36. A middle-aged man is admitted to the hospital for further workup of a suspected malignancy. Which of the following defense mechanisms is most likely to be observed in this individual? a. b. c. d. e. Rationalization Projection Displacement Sublimation Denial 3-37. A 68-year-old man goes to a sleep clinic after he has repeated episodes of loud snoring during sleep coupled with sudden periods of restlessness and cessation of breathing. After extensive analysis, the physicians concluded that the patient’s problem was not a result of obstructive sleep. Instead, it was judged that this condition reflected central sleep apnea due to loss of chemoreceptor sensitivity of the neuronal control mechanisms governing respiration. The most likely site within the CNS that is most closely associated with these effects is the a. b. c. d. e. Dorsal horn of the thoracic spinal cord Reticular formation of the medulla Midbrain periaqueductal gray Hippocampal formation Border of occipital and parietal lobes 3-38. A 26-year-old man contracted viral influenza with an unremitting fever of 39.5°C (103°F) for three days. Because spermatogenesis cannot occur above a scrotal temperature of 35.5°C (96°F), he was left with no viable sperm on his recovery. The time required for spermatogenesis, spermiogenesis, and passage of viable sperm to the epididymis is approximately a. b. c. d. e. 3 days 1 week 5 weeks 2 months 4 months
  • 64 Clinical Vignettes for the USMLE Step 1 3-39. A 35-year-old male has renal stones and increased calcium (Ca) in the urine that is associated with normal serum Ca and parathyroid hormone levels. Which of the following agents could be used to treat this patient? a. b. c. d. e. Furosemide Acetazolamide Triamterene Hydrochlorothiazide Vasopressin
  • Block 3 Questions 65 3-40. The MRI scan in the figure below reveals a large chromophobe adenoma (T) of the pituitary that impinges on the adjoining brain tissue. This tumor caused a a. b. c. d. e. Binasal hemianopsia Bitemporal hemianopsia Loss of the accommodation reflex Loss of the pupillary light reflex Loss of conjugate gaze
  • 66 Clinical Vignettes for the USMLE Step 1 3-41. A middle-aged man has undergone a series of biofeedback sessions to control brief elevations in blood pressure under stressful situations. The most important component of this treatment is a. b. c. d. e. Feelings Information Motivation Attitude Interpersonal relations 3-42. A 67-year-old male is found on rectal examination to have a single, hard, irregular nodule within his prostate. A biopsy of this lesion reveals the presence of small glands lined by a single layer of cells with enlarged, prominent nucleoli. From what portion of the prostate did this lesion most likely originate? a. b. c. d. e. Anterior zone Central zone Peripheral zone Periurethral glands Transition zone 3-43. A 60-year-old woman recently was widowed when her husband died suddenly in an acute myocardial infarction. You are seeing her in a primary care practice for a variety of nonspecific complaints. She is clearly in the midst of grieving for her husband. She is likely to have which of the following physiologic changes? a. b. c. d. e. Decreased responsiveness of lymphocytes to mitogens Decreased corticotrophin-releasing hormone levels Decreased responsiveness of serotonin-3 receptors Decreased sensitivity of α-adrenergic receptors Decreased antibody titers to Epstein-Barr virus
  • Block 3 Questions 67 3-44. A 22-year-old woman marathon runner comes into the office complaining of amenorrhea for 8 months. There has been no weight change, and the serum pregnancy test is negative. She has never been pregnant. Menarche was at 13 years of age, and she had monthly menses until 8 months ago. Physical exam shows a women who is 66 inches tall, 90 pounds, and is otherwise fully normal. Why does she have amenorrhea? a. b. c. d. e. Hypothyroidism Prolactinoma Early menopause Resistance to LH and FSH Excessive exercise 3-45. A 9-year-old child is brought to the emergency room with the chief complaint of enlarged, painful axillary lymph nodes. The resident physician also notes a small, inflamed, dime-sized lesion surrounding what appears to be a small scratch on the forearm. The lymph node is aspirated and some pus is sent to the laboratory for examination. A Warthin-Starry silver impregnation stain reveals many highly pleomorphic, rod-shaped bacteria. The most likely cause of this infection is a. b. c. d. e. Y. pestis Yersinia enterocolitica Mycobacterium scrofulaceum B. canis Bartonella henselae 3-46. A man, the victim of several knife wounds to the abdomen during a barroom brawl, subsequently developed a direct inguinal hernia. Damage to which of the following nerves is most likely responsible for the predisposing weakness of the abdominal wall? a. b. c. d. e. Genitofemoral nerve Ilioinguinal nerve The subcostal nerve Pelvic splanchnic nerves The nerve of the tenth intercostal space (T10)
  • 68 Clinical Vignettes for the USMLE Step 1 3-47. A 10-year-old male displays hyperactivity and is unable to focus on his schoolwork because of an inability to focus on the activity. Which of the following might prove effective in this patient? a. b. c. d. e. f. Methylphenidate Terbutaline Dobutamine Pancuronium Prazosin Scopalamine 3-48. A full-term male infant displays projectile vomiting 1 h after suckling. There is failure to gain weight during the first two weeks. The vomitus is not bile-stained and no respiratory difficulty is evident. Examination reveals an abdomen neither tense nor bloated. The most probable explanation is a. b. c. d. e. Congenital hypertrophic pyloric stenosis Duodenal atresia Patent ileal diverticulum Imperforate anus Tracheoesophageal fistula 3-49. You have been designated as coordinator of construction of a bone marrow transplant unit (BMTU). There will be extensive removal of walls and floors in order to install the laminar flow rooms required for a BMTU. From the standpoint of frequency and lethality, which one of the following fungi should be your biggest concern? a. b. c. d. e. Aspergillus Candida Wangiella Cryptococcus Blastomyces 3-50. A patient on long-term lithium comes into your office complaining of polyuria; you would expect his serum sodium to be a. b. c. d. Elevated because he has central diabetes insipidus Elevated because he has nephrogenic diabetes insipidus Nearly normal because he is drinking increased amounts of water Low because he is suffering from psychogenic polydipsia
  • BLOCK 4 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • BLOCK 4 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Questions 4-11. A 38-year-old female presents with the new onset of multiple purpuric skin lesions. Two years ago she developed late-onset asthma and mild hypertension. Laboratory examination reveals an increase in the number of eosinophils in the peripheral blood (peripheral eosinophilia), and a biopsy from one of the purpuric skin lesions reveals leukocytoclastic vasculitis. No perivascular IgA deposits are found, and no antineutrophil cytoplasm autoantibodies are present. Which one of the listed disorders is the best diagnosis for this individual? a. b. c. d. e. Churg-Strauss syndrome Henoch-Schönlein purpura Macroscopic polyarteritis nodosa Microscopic polyangiitis Wegener’s granulomatosis 71
  • 72 Clinical Vignettes for the USMLE Step 1 4-2. A 28-year-old woman presents to the office with 2 days of abdominal pain and a positive pregnancy test. Her last menstrual period was 9 weeks ago. She reports no dysuria. She reports a history of two episodes of pelvic inflammatory disease. Which of these is the most likely cause of the abdominal pain? a. b. c. d. e. Endometriosis Urinary tract infection Ectopic pregnancy Placental abruption Premenstrual syndrome 4-3. Sudden standing evokes the baroreceptor reflex. Which one of the following will be greater after a person suddenly stands up than it was before the person stood? a. b. c. d. e. The end-diastolic volume The renal blood flow The venous return The pulse pressure The ejection fraction Questions 4-4 to 4-5 A 45-year-old plumber presented in the clinic complaining of longstanding pain in the elbow. Subsequent examination revealed normal flexion/ extension at both the elbow and the wrist but weakened abduction of the thumb and extension at the metacarpophalangeal joints of the fingers. These symptoms were found to be caused by entrapment of the posterior interosseus nerve. 4-4. Which of the following muscles could be expected to demonstrate normal contraction? a. b. c. d. e. Extensor indices Extensor digitorum Extensor carpi radialis longus Abductor pollicis longus Extensor digit minimi
  • Block 4 Questions 73 4-5. Which of the following muscles could itself cause entrapment of the posterior interosseus nerve? a. b. c. d. e. Extensor carpi ulnaris Extensor indices Anconeus Extensor digitorum Supinator 4-6. A 72-year-old female with a long history of anxiety treated with diazepam decides to triple her dose because of increasing fearfulness about “environmental noises.” Several days after her attempt at self-prescribing, her neighbor finds her to be extremely lethargic and nonresponsive. On examination, she is found to be stuporous and have diminished reaction to pain and decreased reflexes. Her respiratory rate is 8 breaths per minute (BPM), and she has shallow respirations. Which antidote could be given to reverse these findings? a. b. c. d. Naltrexone Physostigmine Pralidoxime Flumazenil
  • 74 Clinical Vignettes for the USMLE Step 1 4-7. A 22-year-old female presents with fever, weight loss, night sweats, and painless enlargement of several supraclavicular lymph nodes. A biopsy from one of the enlarged lymph nodes is shown in the photomicrograph below. The binucleate or bilobed giant cell with prominent acidophilic “owl-eye” nucleoli shown is a a. b. c. d. e. Call-Exner cell Hürthle cell Reed-Sternberg cell Sézary cell Strap cell 4-8. A 25-year-old female post–renal transplant shows signs of acute renal allograph rejection. Of the following agents, which should be administered? a. b. c. d. e. Interferon α Aldesleukin Muromonab-CD3 Sargramostim Filgrastim
  • Block 4 Questions 75 4-9. Upon examination, a patient is unable to move his right eye medially. The lesion is likely to be located in the a. b. c. d. e. Dorsal medulla Ventromedial medulla Dorsal pons Ventromedial pons Medial midbrain 4-10. A young woman has recently completed an inpatient program for alcohol dependence. Using the classical conditioning model, the patient’s risk of relapse is increased if she is a. Maintained in an environment free of alcohol-associated stimuli b. Provided therapeutic strategies to extinguish alcohol-compensatory conditioned responses c. Returned to an environment different from the one in which the dependence was acquired d. Provided procedures to extinguish conditioned associations between aversive affective states and alcohol e. Allowed to substitute the use of other nonalcoholic drugs when negative affective states occur 4-11. A 24-year-old male visited the community clinic complaining of a draining abscess on his anterior thigh. Subsequent testing revealed an active tuberculosis infection localized in the lumbar vertebrae. The spread of infection most likely occurred via a. b. c. d. The ischiorectal fossa The sheath of the psoas muscle The inguinal ligament A paracolic gutter 4-12. A 65-year-old male has a blood pressure of 170/105 mmHg. Which of the following would be effective in lowering this patient’s blood pressure? a. b. c. d. e. f. Methylphenidate Terbutaline Dobutamine Pancuronium Prazosin Scopalamine
  • 76 Clinical Vignettes for the USMLE Step 1 4-13. A middle-aged patient with an elevated serum creatinine, hypertension, and mild anemia comes to you for evaluation. Urine dipstick shows trace protein without red cells or cellular casts. A 24-h urine collection reveals 5 g of protein. The most likely etiology is a. b. c. d. Focal segmental sclerosis Hypertensive nephrosclerosis Amyloidosis Multiple myeloma 4-14. Bleeding time is determined by nicking the skin superficially with a scalpel blade and measuring the time required for hemostasis. It will be markedly abnormal (prolonged) in a person who a. b. c. d. e. Lacks factor VIII Cannot absorb vitamin K Has liver disease Takes large quantities of aspirin Takes coumarin derivatives 4-15. A 3-year-old child is brought into the ER while you are on duty. She is cold and clammy and is breathing rapidly. She is obviously confused and lethargic. Her mother indicates she has accidentally ingested automobile antifreeze while playing in the garage. Following gastrointestinal lavage and activated charcoal administration, one of the treatments you immediately initiate involves a. b. c. d. e. Intravenous infusion of oxalic acid Nasogastric tube for ethanol administration Flushing out the bladder via a catheter Intramuscular injection of epinephrine Simply waiting and measuring vital signs 4-16. An obstetrician sees a pregnant patient who was exposed to rubella virus in the eighteenth week of pregnancy. She does not remember getting a rubella vaccination. The best immediate course of action is to a. Terminate the pregnancy b. Order a rubella antibody titer to determine immune status c. Reassure the patient because rubella is not a problem until after the thirtieth week d. Administer rubella immune globulin e. Administer rubella vaccine
  • Block 4 Questions 77 4-17. The bone marrow biopsy shown in the photomicrograph below was performed because of splenomegaly and anemia in an adult. On the basis of the appearance of the bone marrow core, the most likely diagnosis is a. b. c. d. e. Chronic myeloid leukemia (CML) Aplastic anemia Acute leukemia Myeloid metaplasia with myelofibrosis Microangiopathic hemolytic anemia 4-18. A 60-year-old female with deep-vein thrombosis (DVT) is given a bolus of heparin, and a heparin drip is also started. Thirty minutes later, she is bleeding profusely from the intravenous site. The heparin is stopped, but the bleeding continues. You decide to give protamine to reverse the adverse effect of heparin. How does protamine act? a. b. c. d. It causes hydrolysis of heparin It changes the conformation of antithrombin III to prevent binding to heparin It activates the coagulation cascade, overriding the action of heparin It combines with heparin as an ion pair, thus inactivating it
  • 78 Clinical Vignettes for the USMLE Step 1 4-19. Leukocyte samples isolated from the blood of a newborn infant are homogenized and incubated with ganglioside GM2. Approximately 47% of the expected normal amount of N-acetylgalactosamine is liberated during the incubation period. These results indicate that the infant a. b. c. d. e. Is a heterozygote (carrier) for Tay-Sachs disease Is homozygous for Tay-Sachs disease Has Tay-Sachs syndrome Will most likely have mental deficiency Has relatively normal β-N-acetylhexosaminidase activity 4-20. A 70-year-old man presents to you because he has not been feeling well for several months. He mainly complains of malaise and achiness. He takes ibuprofen occasionally for these symptoms. His urine shows protein and erythrocyte casts. A 24-h urine shows 1 g of protein per day. His creatinine clearance is 24 mL/min. About 4 months ago, his serum creatinine was normal. The most likely diagnosis is a. b. c. d. Amyloidosis Light chain deposition disease Nonsteroidal induced interstitial nephritis Vasculitis 4-21. A 60-year-old male complains of severe headaches, nausea, dizziness, and a diminution in vision. He has a decrease in oxygen (O2)-carrying capacity without a change in the PO2 of arterial blood. Which of the following might account for these findings? a. b. c. d. e. Sulfur dioxide Ozone Nitrogen dioxide Carbon monoxide (CO) Methane Questions 4-22 through 4-23 A 46-year-old bakery worker is admitted to a hospital in acute distress. She has experienced severe abdominal pain, nausea, and vomiting for two days. The pain, which is sharp and constant, began in the epigastric region and radiated bilaterally around the chest to just below the scapulas. Subsequently, the pain became localized in the right hypochondrium. The patient, who has a history of similar attacks after hearty meals over the past
  • Block 4 Questions 79 five years, is moderately overweight and the mother of four. Palpation reveals marked tenderness in the right hypochondriac region and some rigidity of the abdominal musculature. An x-ray without contrast medium shows numerous calcified stones in the region of the gallbladder. The patient shows no sign of icterus (jaundice). 4-22. Diffuse pain referred to the epigastric region and radiating circumferentially around the chest is the result of afferent fibers that travel via which of the following nerves? a. b. c. d. Greater splanchnic Intercostal Phrenic Vagus 4-23. The above patient receives a general anesthetic in preparation for a cholecystectomy. A right subcostal incision is made, which begins near the xiphoid process, runs along and immediately beneath the costal margin to the anterior axillary line, and transects the rectus abdominis muscle and rectus sheath. At the level of the transpyloric plane, the anterior wall of the sheath of the rectus abdominis muscle receives contributions from the a. Aponeuroses of the internal and external oblique muscles b. Aponeuroses of the transversus abdominis and internal oblique muscles c. Aponeuroses of the transversus abdominis and internal and external oblique muscles d. Transversalis fascia e. Transversalis fascia and aponeurosis of the transversus abdominis muscle 4-24. A 30-year-old male with a two-year history of chronic renal failure requiring dialysis consents to transplantation. A donor kidney becomes available. He is given cyclosporine to prevent transplant rejection just before surgery. What is the most likely adverse effect of this drug? a. b. c. d. e. Bone marrow depression Nephrotoxicity Oral and GI ulceration Pancreatitis Seizures
  • 80 Clinical Vignettes for the USMLE Step 1 4-25. A 47-year-old male presents with the sudden onset of fever, chills, and dysuria. During the review of symptoms you discover that he has no history of recurrent urinary tract infections. Rectal examination finds that the prostate gland is very sensitive and examination is painful. What is the most likely diagnosis for this patient? a. b. c. d. e. Acute prostatitis Chronic bacterial prostatitis Chronic abacterial prostatitis Granulomatous prostatitis Benign prostatic hyperplasia
  • Block 4 Questions 81 YOU SHOULD HAVE COMPLETED APPROXIMATELY 25 QUESTIONS AND HAVE 30 MINUTES REMAINING. 4-26. An 82-year-old woman presents with headaches, visual disturbances, and muscle pain. A biopsy of the temporal artery is shown in the associated photomicrograph. The next course of action is to a. b. c. d. e. Administer corticosteroids Verify with a repeat biopsy Administer anticoagulants Perform angiography Order a test of the erythrocyte sedimentation rate
  • 82 Clinical Vignettes for the USMLE Step 1 4-27. The following test results were observed in a woman tested in November who reported being in the woods in Pennsylvania during the past summer, was bitten by a tick, and now has Bell’s palsy: Lyme IgG antibody 1:1280; Lyme IgM antibody negative. Which one of the following courses of action is most appropriate? a. Order tests for syphilis (VDRL, FTA-ABS) because there are cross-reactions reported with Borrelia burgdorferi b. Ask the patient if she has a severe headache c. Consider treatment of the patient with an appropriate antibiotic such as tetracycline d. Ask the patient if she has had a urinary tract infection with E. coli e. Ignore the results because there is no Lyme disease in Pennsylvania
  • Block 4 Questions 83 4-28. Your patient reports he spent two weeks on a desert island as part of a television survival show. It rained and was cool the last five days and he developed a cough. He is now in the ER with a productive cough that produces rusty and bloodstained sputum. He also complains of significant pleural pain. You suspect a pneumococcal lobar pneumonia. From this CT scan at the T4 level, which lung lobe (indicated by the *) is involved with the pneumonia? a. b. c. d. e. Right upper lobe Right middle lobe Right lower lobe Left upper lobe Left lower lobe
  • 84 Clinical Vignettes for the USMLE Step 1 4-29. A 60-year-old male with AIDS develops a systemic fungal infection that is treated with fluconazole. What is the mechanism of action of fluconazole? a. b. c. d. It inhibits ergosterol synthesis It inhibits DNA synthesis It inhibits peptidoglycan synthesis It inhibits protein synthesis 4-30. You are working up a middle-aged patient who has moderate essential hypertension. You start the patient on an initial pharmacologic requiem of an ACE inhibitor. Which behavioral risk factors would you approach first in your long-term follow-up of the patient? a. b. c. d. Type A personality Dietary salt intake Stress in the workplace Obesity 4-31. A section of tissue from the foot of a person assumed to have eumycotic mycetoma shows a white, lobulated granule composed of fungal hyphae. In the United States, the most common etiologic agent of this condition is a species of a. b. c. d. e. Acremonium Nocardia Actinomyces Pseudallescheria (Petriellidium) Madurella 4-32. A 55-year-old man who is a longtime alcoholic comes to the emergency room after vomiting small amounts of bright red blood four times today. Your differential diagnosis is constructed around causes of bleeding from the a. b. c. d. e. Colon Liver and pancreas Kidneys Lungs Upper gastrointestinal (GI) tract
  • Block 4 Questions 85 4-33. A 5-year-old girl displays decreased appetite, increased urinary frequency, and thirst. Her physician suspects new-onset diabetes mellitus and confirms that she has elevated urine glucose ketones. Which of the following blood values would be most compatible with diabetic ketoacidosis? a. b. c. d. e. pH 7.05 7.25 7.40 7.66 7.33 Bicarbonate (mM) 16.0 20.0 24.5 37.0 12.0 Arterial PCO2 52 41 39 30 21 4-34. A 71-year-old female presents with the sudden onset of severe lower back pain. Physical examination reveals severe kyphosis, while an x-ray of her back reveals a compression fracture of a vertebral body in the lumbar area along with marked thinning of the bones. Serum calcium, phosphorus, alkaline phosphatase, and parathyroid hormone levels are all within normal limits. This woman’s bone changes are most likely due to a. b. c. d. e. Osteopetrosis Osteoporosis Osteomalacia Osteitis fibrosa cystica Osteitis deformans 4-35. A 40-year-old female post–renal transplant has developed evidence of osteoporosis, most likely due to cyclosporine. Which of the following agents might replace cyclosporine? a. b. c. d. e. f. g. h. i. Allopurinol Asparaginase Methotrexate Streptozocin 6-MP Azathioprine Pentostatin Leucovorin BCG vaccine
  • 86 Clinical Vignettes for the USMLE Step 1 4-36. A medical technologist visited Scandinavia and consumed raw fish daily for 2 weeks. Six months after her return home, she had a routine physical and was found to be anemic. Her vitamin B12 levels were below normal. The most likely cause of her vitamin B12 deficiency anemia is a. b. c. d. e. Excessive consumption of ice-cold vodka Infection with parvovirus B 19 Infection with the fish tapeworm D. latum Infection with Yersinia Cysticercosis Questions 4-37 to 4-38 As a result of a leg injury, a 30-year-old male developed chronic pain and was subsequently treated with morphine. Consequently, he developed an addiction to morphine. 4-37. The predominant site where this effect is mediated is the a. b. c. d. e. Opioid nociceptin receptor Opioid µ receptor Opioid δ receptor Opioid κ receptor Dopamine D2-receptor 4-38. A region of the brain where this receptor has been shown through extensive research to be heavily concentrated is the a. b. c. d. e. Mammillary bodies Precentral gyrus Midbrain periaqueductal gray Inferior olivary nucleus Deep pontine nuclei
  • Block 4 Questions 87 4-39. A newborn with tachypnea and cyanosis (bluish color) is found to have a blood pH of 7.1. A serum bicarbonate is measured as 12 mM, but the blood gas machine that would determine the partial pressures of oxygen (PO2) and carbon dioxide (PCO2) is broken. Recall the pKa of 6.1 for carbonic acid (reflecting the HCO3−/CO2 equilibrium in blood) and the fact that the blood CO2 concentration is equal to the PCO2 in mmHg (normal value = 40 mmHg) multiplied by 0.03. Which of the following treatment strategies is indicated? a. b. c. d. e. Administer oxygen to improve tissue perfusion and decrease metabolic acidosis Administer oxygen to decrease respiratory acidosis Increase the respiratory rate to treat respiratory acidosis Decrease the respiratory rate to treat respiratory acidosis Administer medicines to decrease renal hydrogen ion excretion 4-40. A butcher, who is fond of eating raw hamburger, develops chorioretinitis; a Sabin-Feldman dye test is positive. This patient is most likely infected with a. b. c. d. e. Trichinosis Schistosomiasis Toxoplasmosis Visceral larva migrans Giardiasis 4-41. A teenage girl presents for evaluation of hearing loss in her right ear. She has a history of at least 12 episodes of otitis media as a child; at least one time she perforated her ear drum. Her hearing loss is classified as a. b. c. d. e. Conductive deafness Sensorineural deafness Central deafness Tinnitus Presbycusis 4-42. A 70-year-old female is treated with sublingual nitroglycerin for her occasional bouts of angina. Which of the following is involved in the action of nitroglycerin? a. b. c. d. e. α-adrenergic activity Phosphodiesterase activity Phosphorylation of light chains of myosin Norepinephrine release cGMP
  • 88 Clinical Vignettes for the USMLE Step 1 4-43. A 49-year-old man develops an acute myocardial infarction because of the sudden occlusion of the left anterior descending coronary artery. The areas of myocardial necrosis within the ventricle can best be described as a. b. c. d. e. Coagulative necrosis Liquefactive necrosis Fat necrosis Caseous necrosis Fibrinoid necrosis Questions 4-44 to 4-45 4-44. The patient whose CT scan is shown in the figure above sustained an occlusion of a major artery on the left side of the brain. The most prominent deficits will most likely include a. b. c. d. e. A right homonymous hemianopsia only Aphasia only A right homonymous hemianopsia coupled with aphasia Marked intellectual deficits Marked intellectual deficits coupled with hemiballism
  • Block 4 Questions 89 4-45. The blood vessel occluded in the above figure is the a. b. c. d. e. Anterior cerebral artery Middle cerebral artery Posterior cerebral artery Posterior choroidal artery Superior cerebellar artery 4-46. You are designing a weight-reduction program for a patient with long-term obesity. You wish to use a group of behavioral techniques that derive from the principle of stimulus control. Which of these instructions would be consistent with this plan? a. b. c. d. e. Watching TV or reading when eating Eating only when hungry, not at specific times Eating in a variety of different places Shopping for groceries only when hungry Eating at specific times and places 4-47. A 50-year-old woman executive has for the past 3 months experienced abdominal pain that often is relieved by antacids. Because of the persistent abdominal pain, she consults a gastroenterologist. He does an upper GI endoscopy and visualizes a duodenal ulcer. Now, the gastroenterologist should a. b. c. d. e. Biopsy the ulcer Arrange for a surgeon to operate on the ulcer Suggest medical treatment of the ulcer Cauterize the ulcer Order an abdominal CT scan 4-48. A 15-year-old male comes into the office complaining about a lack of pubic hair growth. He also informs you that his voice has not yet deepened, and he has no interest in sexual activity. He is an only child. Blood drawn reveals a very high testosterone level. What is the problem? a. b. c. d. e. Low FSH and LH High FSH and LH Androgen insensitivity Hyperthyroidism XXY karyotype
  • 90 Clinical Vignettes for the USMLE Step 1 4-49. A 19-year-old female presents with urticaria that developed after she took aspirin for a headache. She has a history of chronic rhinitis, and physical examination reveals the presence of nasal polyps. This patient is at an increased risk of developing which one of the following pulmonary diseases following the ingestion of aspirin? a. b. c. d. e. Asthma Chronic bronchitis Emphysema Interstitial fibrosis Pulmonary hypertension 4-50. A 60-year-old male with hematuria is found to have a small localized tumor of the bladder that is diagnosed as a carcinoma. Which of the following agents should be given intravesicularly? a. b. c. d. e. f. g. h. i. Allopurinol Asparaginase Methotrexate Streptozocin 6-MP Azathioprine Pentostatin Leucovorin BCG vaccine
  • BLOCK 5 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • BLOCK 5 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Questions 5-1. A 32-year-old male presents with scrotal enlargement. Physical examination, including scrotal transillumination, reveals the presence of a testicular cyst containing clear fluid. This abnormality most likely results from fluid accumulating within the a. b. c. d. e. Ampulla of the ductus deferens Appendix testis Epididymis Seminal vesicles Tunica vaginalis 5-2. A patient displays an ipsilateral paralysis of lateral gaze coupled with a contralateral hemiplegia. A lesion is most likely situated in the a. b. c. d. e. Ventromedial medulla Dorsomedial medulla Ventrocaudal pons Dorsorostral pons Ventromedial midbrain 93
  • 94 Clinical Vignettes for the USMLE Step 1 5-3. A 47-year-old male presents with pain in the midportion of his chest. The pain is associated with eating and swallowing food. Endoscopic examination reveals an ulcerated area in the lower portion of his esophagus. Histologic sections of tissue taken from this area reveal an ulceration of the esophageal mucosa that is filled with blood, fibrin, proliferating blood vessels, and proliferating fibroblasts. Mitoses are easily found, and most of the cells have prominent nucleoli. Which one of the following correctly describes this ulcerated area? a. b. c. d. e. Caseating granulomatous inflammation Dysplastic epithelium Granulation tissue Squamous cell carcinoma Noncaseating granulomatous inflammation 5-4. A 45-year-old obese woman with cholelithiasis presents to the emergency room complaining of nausea and vomiting for 2 days, along with severe continuous midabdominal pain. She has a low-grade fever and the ER physician finds that she has a slightly elevated WBC count (12,000) and an elevated serum amylase. The most likely diagnosis is a. b. c. d. e. Ruptured abdominal aortic aneurysm Hepatitis Peptic ulcer disease Early phase of acute appendicitis Acute pancreatitis
  • Block 5 Questions 95 5-5. A 22-year-old male who belongs to a weekend football league was running with the ball when a defender tackled him mid-lower limb from the side. After the tackle, he felt that the knee was hurt and went to the emergency room. From an MRI of the knee, the lateral meniscus is uniformly black; however, the medial meniscus has a tear (lucent area within the meniscus). Which of the following is the reason why the medial meniscus is more susceptible to damage than the lateral meniscus? a. The medial meniscus is attached to the popliteus muscle tendon, which can move into a position making it more susceptible. b. The medial meniscus is attached to the medial (tibial) collateral ligament, which holds it relatively immobile, making it more susceptible. c. The medial meniscus is attached to the anterior cruciate ligament, which holds it relatively immobile, making it more susceptible. d. The only reason the medial meniscus is more susceptible to damage is that the knee usually gets hit laterally, causing more torsion on the medial meniscus.
  • 96 Clinical Vignettes for the USMLE Step 1 5-6. A fur trapper complains of sore muscles, has swollen eyes, and reports eating bear meat on a regular basis. He is at risk for a. b. c. d. e. Trichinosis Schistosomiasis Toxoplasmosis Visceral larva migrans Giardiasis 5-7. A newborn female infant develops edema, jaundice, and trouble breathing. The blood type of the mother is AB negative, while the baby and the father are both B positive. The mother’s only other pregnancy was unremarkable, and she has never received any blood or blood products. Laboratory examination reveals a positive Coombs (DAT) test. What is the best diagnosis? a. b. c. d. e. ABO hemolytic disease of the newborn Hemoglobin H disease Hyaline membrane disease of the newborn Hydrops fetalis Rh hemolytic disease of the newborn 5-8. A 45-year-old female has a bone marrow transplant for treatment of ovarian cancer. Cyclosporine is given as an immunosuppressant. What is the mechanism of action of cyclosporine? a. b. c. d. e. Direct destruction of proliferating lymphoid cells Inhibition of T cell response to cytokines Inhibition of folic acid metabolism Inhibition of factors that stimulate T cell growth Inhibition of enzymes that are related to purine metabolism 5-9. A 60-year-old male has high blood pressure and the diagnosis indicates that it is due in part to retention of water. Which of the following compounds would most likely relate to this process? a. b. c. d. e. Oxytocin Serotonin Histamine Vasopressin Somatostatin
  • Block 5 Questions 97 5-10. A 45-year-old man has a mild heart attack and is placed on diet and mevastatin therapy. Which of the following will be a result of this therapy? a. b. c. d. e. f. g. Low blood glucose Low blood LDLs High blood cholesterol High blood glucose Low oxidation of fatty acids Ketosis Lipolysis 5-11. A 19-year-old pregnant female feels tired and out of pep. Her conjunctivae are pale; laboratory tests show she has a mild normocytic, normochromic anemia with a low serum iron and an increased TIBC (transferrin iron-binding capacity). Hemoccult tests are negative. Which is the likely cause of her anemia? a. b. c. d. e. Gastrointestinal bleeding Iron or folate deficiencies Autoantibodies Vitamin B12 deficiency Menstrual blood loss 5-12. A 75-year-old male develops a cough that produces blood-tinged sputum. He has a fever of 104°F Gram-positive cocci in clusters are found . in a sputum smear. A chest x-ray shows increased density in the right upper lobe. Of the following penicillins, which is most likely to be ineffective? a. b. c. d. e. Oxacillin Cloxacillin Ticarcillin Nafcillin Dicloxacillin
  • 98 Clinical Vignettes for the USMLE Step 1 5-13. A 28-year-old woman comes into the emergency room exhibiting dyspnea and mild cyanosis, but no signs of trauma. Her chest x-ray is shown below. The most obvious abnormal finding in the inspiratory posteroanterior chest x-ray of this patient (viewed in the anatomic position) is a a. b. c. d. e. Bilateral expansion of the pleural cavities above the first rib Grossly enlarged heart Left pneumothorax (collapsed lung) Paralysis of the left hemidiaphragm Right hemothorax (blood in the pleural cavity) 5-14. A 34-year-old patient with chronic schizophrenia is hospitalized on a chronic ward of a psychiatric hospital and is on an appropriate dose of antipsychotic medication. He frequently shouts in the halls, disrupting activities and annoying the other patients. The best behavioral strategy for this patient would be a. b. c. d. e. Psychological counseling Contingency management Stimulus control Role-play therapy Modeling
  • Block 5 Questions 99 5-15. A patient is confused and displays localized jerks in his right hand, which progress to jerks of the entire arm with a brief loss of consciousness. This disorder can best be characterized as a a. b. c. d. e. Generalized seizure Absence seizure Simple partial seizure Complex partial seizure Petit mal seizure 5-16. A 2-year-old child was admitted to the hospital with acute meningitis. The Gram stain revealed Gram-positive short rods, and the mother indicated that the child had received “all” of the meningitis vaccinations. What is the most likely cause of the disease? a. b. c. d. e. N. meningitidis, group A N. meningitidis, group C Listeria S. pneumoniae H. influenzae 5-17. A 5-year-old boy presents with clumsiness, a waddling gait, and difficulty climbing steps. Physical examination reveals that this boy uses his arms and shoulder muscles to rise from the floor or a chair. Additionally, his calves appear to be somewhat larger than normal. This boy’s physical findings are most consistent with a diagnosis of a. b. c. d. e. Inclusion body myositis Werdnig-Hoffmann disease Dermatomyositis Duchenne’s muscular dystrophy Myotonic dystrophy
  • 100 Clinical Vignettes for the USMLE Step 1 5-18. A child is referred for evaluation because of low muscle tone and developmental delay. Shortly after delivery the child was a poor feeder and had to be fed by tube. In the second year, the child began to eat voraciously and became obese. He has a slightly unusual face with almond-shaped eyes and downturned corners of the mouth. The hands, feet, and penis are small, and the scrotum is poorly formed. The diagnostic category and laboratory test to be considered for this child are a. b. c. d. e. Sequence, serum testosterone Single birth defect, serum testosterone Deformation, karyotype Syndrome, karyotype Disruption, karyotype 5-19. A 70-year-old man complains of a sensation of food sticking in his lower chest area. This happens when he eats either liquids or solids. He also has a slight weight loss. The most likely diagnosis is a. b. c. d. e. Achalasia Esophageal spasm Hypertensive LES Hiatal hernia with GERD Barrett’s esophagus 5-20. A 16-year-old male treated for acute lymphocytic leukemia develops severe lumbar and abdominal pain. His serum amylase is markedly elevated. Which of the following agents most likely caused these findings? a. b. c. d. e. 6-MP Asparaginase Doxorubicin Methotrexate Vincristine
  • Block 5 Questions 101 5-21. A middle-aged woman has developed a pattern of compulsive eating of snack foods and fast foods from restaurant chains, in response to tension and anxiety. Over several years she has gained 80 lbs from a normal weight for her height. This pathologic eating behavior is most likely to predispose the patient to a. b. c. d. e. Diabetes mellitus Atherosclerosis Hypertension Sleep apnea Gallstones 5-22. A 40-year-old man with occasional dysphagia and who otherwise feels well undergoes esophageal motility studies that show an LES amplitude of approximately 60 mmHg. The esophagus relaxes completely when he swallows. The most likely diagnosis is a. b. c. d. e. GERD (gastroesophageal reflux disease) Achalasia Hypertensive LES Barrett’s esophagus Esophageal spasm 5-23. A newborn with ambiguous genitalia and a 46,XY karyotype develops vomiting, low serum sodium concentration, and high serum potassium. Which of the following proteins is most likely to be abnormal? a. b. c. d. e. 21-hydroxylase An ovarian enzyme 5α-reductase An androgen receptor A testicular enzyme
  • 102 Clinical Vignettes for the USMLE Step 1 Questions 5-24 through 5-25 Herb, a 62-year-old man who has smoked two packs of cigarettes per day for 35 years, was suffering from a chronic cough that was attributed to smoking habit by his physician. One day, Herb noticed that his right eyelid drooped slightly and that his right pupil was smaller than the left. He also noticed that the inner side of his right hand was numb and that he had begun to drop things from his right hand. He had no other symptoms. Herb consulted his physician who directed him to a neurologist. The neurologist noted that although the right pupil was smaller than the left, it was still reactive to light. Although Herb’s right eyelid drooped slightly, he could close his eyes tightly when asked to do so. The neurologist noted that Herb did not sweat on the right side of his face. He was unable to feel a pinprick on the inner surface of his right hand, and his right triceps and hand muscles were weak. 5-24. Where in the nervous system has damage occurred? a. b. c. d. Left oculomotor nerve Right oculomotor nerve Edinger-Westphal nucleus Sympathetic fibers coursing from the hypothalamus to the intermediolateral cell column e. Parasympathetic fibers coursing from the Edinger-Westphal nucleus 5-25. Herb’s small pupil is due to a. b. c. d. e. Unopposed action of the muscles with parasympathetic innervation Unopposed action of the muscles with sympathetic innervation Both sympathetic and parasympathetic damage A lesion in the nucleus of the third nerve A lesion distal branches of the trochlear nerve
  • Block 5 Questions 103 YOU SHOULD HAVE COMPLETED APPROXIMATELY 25 QUESTIONS AND HAVE 30 MINUTES REMAINING. 5-26. A 50-year-old patient has just lost his wife of 30 years and is suffering from the acute stress of bereavement. Without medical intervention such as supervision of factors affecting his mental and physical health, recommendation of support groups, and the scheduling of regular visits over the next six months, the patient will be subject to an increased mortality risk of a. b. c. d. e. 10% 20% 30% 40% 50% 5-27. A teenager who works in a dog kennel after school has had a skin rash, eosinophilia, and an enlarged liver and spleen for 2 years. The most likely cause of this infection is a. b. c. d. e. Trichinosis Schistosomiasis Toxoplasmosis Visceral larva migrans Giardiasis
  • 104 Clinical Vignettes for the USMLE Step 1 5-28. An Asian child has severe anemia with prominence of the forehead (frontal bossing) and cheeks. The red cell hemoglobin concentration is dramatically decreased, and it contains only β-globin chains with virtual deficiency of α-globin chains. Which of the following mechanisms is a potential explanation? a. b. c. d. e. A transcription factor regulating the α-globin gene is mutated A regulatory sequence element has been mutated adjacent to an α-globin gene A transcription factor regulating the β-globin gene is mutated A transcription factor regulating the α-globin and β-globin genes is deficient A deletion has occurred surrounding an α-globin gene 5-29. A 23-year-old HIV-positive male presents with a cough and increasing shortness of breath. A histologic section from a transbronchial biopsy stained with Gomori’s methenamine-silver stain is shown in the photomicrograph below. What is the correct diagnosis? a. b. c. d. e. Pseudomonas pneumonia Aspergillus pneumonia Pneumocystis carinii pneumonia Cytomegalovirus pneumonia Influenza pneumonia
  • Block 5 Questions 105 5-30. An enterococcus (E. faecium) was isolated from a urine specimen (100,000 cfu/mL). Treatment of the patient with ampicillin and gentamicin failed. The most clinically appropriate action is a. Do no further clinical workup b. Suggest to the laboratory that low colony counts may reflect infection c. Determine if fluorescent microscopy is available for the diagnosis of actinomycosis d. Consider vancomycin as an alternative drug e. Suggest a repeat antibiotic susceptibility test 5-31. A 16-year-old male treated for bronchial asthma develops skeletal muscle tremors. Which of the following agents may be responsible for this finding? a. b. c. d. e. Ipratropium Zileuton Beclomethasone Cromolyn Salmeterol 5-32. During a routine physical examination, a 42-year-old female is found to have an elevated blood pressure of 150/100 mmHg. Workup reveals a small left kidney and a normal-sized right kidney. Laboratory examination reveals elevated serum renin levels. Further workup reveals that renal vein renin levels are increased on the left but decreased on the right. This patient’s hypertension is most likely the result of a. b. c. d. e. Atherosclerotic narrowing of the left renal artery Atherosclerotic narrowing of the right renal artery Fibromuscular hyperplasia of the left renal artery Fibromuscular hyperplasia of the right renal artery Hyaline arteriolosclerosis
  • 106 Clinical Vignettes for the USMLE Step 1 Questions 5-33 through 5-34 An individual is admitted to the emergency room and is diagnosed as having cortical damage and resultant neuronal degeneration due to an ischemic insult. The neurologist concluded that the brain damage involved neurotoxicity of those cells. 5-33. The neurotransmitter change associated with neurotoxicity in this case is believed to involve a. b. c. d. e. Extracellular accumulation of norepinephrine Extracellular accumulation of ACh Extracellular accumulation of glutamate Extracellular loss of serotonin Extracellular loss of GABA 5-34. The likely mechanism underlying neurotoxicity as a result of ischemia involves a. b. c. d. e. Entry of Ca2+ into the cell Reduction of extracellular chloride Delayed removal of norepinephrine from the synapse Hypersensitivity of the postsynaptic membrane to GABA Failure of degradation of ACh 5-35. A 28-year-old woman presents complaining of infertility. She had a healthy child 3 years ago and has been trying to get pregnant with the child’s father for the last 18 months. She does not have dysmenorrhea. Her menses occur regularly, but these show significantly less flow compared with before her pregnancy. She recalls having a curettage performed to remove placental remnants. What is the most likely diagnosis? a. b. c. d. e. Ovarian failure Hypothyroidism Asherman’s syndrome Endometriosis Prolactinoma
  • Block 5 Questions 107 5-36. A 5-year-old Egyptian boy receives a sulfonamide antibiotic as prophylaxis for recurrent urinary tract infections. Although he was previously healthy and well-nourished, he becomes progressively ill and presents to your office with pallor and irritability. A blood count shows that he is severely anemic with jaundice due to hemolysis of red blood cells. Which of the following would be the simplest test for diagnosis? a. b. c. d. Northern blotting of red blood cell mRNA Enzyme assay of red blood cell hemolysate Western blotting of red blood cell hemolysates Amplification of red blood cell DNA and hybridization with allele-specific oligonucleotides (PCR-ASOs) e. Southern blot analysis for gene deletions 5-37. A 45-year-old male post–myocardial infarction (post-MI) for one week is being treated with intravenous (IV) heparin. Stool guaiac on admission was negative, but is now 4+, and he has had an episode of hematemesis. The heparin is discontinued, and a drug is given to counteract the bleeding. What drug was given? a. b. c. d. e. Aminocaproic acid Dipyridamole Factor IX Protamine Vitamin K
  • 108 Clinical Vignettes for the USMLE Step 1 5-38. Your patient is a 30-year-old male who lives in a group home. He was playing with a pencil and, during a fall, accidentally drove the pencil deeply into a nostril. The pencil was angled toward the midline structure indicated by the arrow in this midsagittal MRI. The pencil was driven toward the (indicated by the arrow). through the a. b. c. d. e. Nasal cavity and nasopharynx, toward the pharyngeal tonsil Nasal cavity and sphenoidal sinus, toward the pituitary Nasal cavity and sphenoidal sinus, toward the internal carotid artery Nasal cavity and ethmoidal air cells, toward the circle of Willis Nasal cavity, toward the basilar artery
  • Block 5 Questions 109 5-39. A patient is being treated by a behavioral technique for a phobia that is precipitated by being in a crowded situation. The patient is taught muscular relaxation; then, while using the relaxation to inhibit the anxiety, the patient is told to imagine a series of progressively more severe anxietyprovoking situations. This technique is called a. b. c. d. e. Modeling Stress inoculation Systematic desensitization Conditioned compensatory response Contingency conditioning 5-40. A 6-year-old female is being evaluated for recurrent episodes of lightheadedness and sweating due to hypoglycemia. These symptoms are not improved by subcutaneous injection of epinephrine. Physical examination reveals an enlarged liver and a single subcutaneous xanthoma. An abdominal CT scan reveals enlargement of the liver along with bilateral enlargement of the kidneys. Laboratory examination reveals increased serum uric acid and cholesterol with decreased serum glucose levels. Following oral administration of fructose, there is no increase in blood glucose levels. A liver biopsy specimen reveals increased amounts of glycogen in hepatocytes, which also have decreased levels of glucose-6-phosphatase. What is the correct diagnosis? a. b. c. d. e. Andersen’s syndrome (type IV glycogen storage disease) Cori’s disease (type III glycogen storage disease) McArdle’s syndrome (type V glycogen storage disease) Pompe’s disease (type II glycogen storage disease) von Gierke’s disease (type I glycogen storage disease) 5-41. A 16-year-old boy takes the drug of abuse, phencyclidine (PCP). The deleterious effects of the drug are due in part to a. b. c. d. e. Blockade of NMDA receptors Blockade of AMPA receptors Blockade of cholinergic receptors Blockade of GABAA receptors Blockade of GABAB receptors
  • 110 Clinical Vignettes for the USMLE Step 1 5-42. Your new patient is a 45-year-old, recently divorced woman. She has just told you that her 25-year-old son returned home three days ago with AIDS, and that she has experienced severe chest pains when she thinks about it. She starts to tell you about some other disturbing symptoms, begins to cry, and looks away. Of the following, which would be the most appropriate immediate response to facilitate the interview? a. b. c. d. e. Silence “I know how you feel” “Don’t worry, it’ll be OK” “Why are you so upset? You know you can tell me anything” “Are you thinking that you may have AIDS?” 5-43. A 45-year-old man complains of frequent “heartburn” and a mild chronic cough. On examination, he has gastroesophageal reflux disease (GERD). In addition to prescribing medications, which one of the following dietary recommendations would you make? a. Avoid high-protein meals because they would increase lower esophageal sphincter (LES) pressure b. Avoid fats, chocolates, and alcohol because they would decrease LES pressure c. Eat high-carbohydrate food to increase overall GI motility d. Eat high-protein meals to decrease LES pressure e. Avoid concentrated carbohydrates to decrease dopamine secretion 5-44. An elderly woman visits the hospital emergency room with the recent onset of grotesque swelling of the right arm, neck, and face. Her right jugular vein is visibly engorged and her right brachial pulse is diminished. On the basis of these signs, her chest x-rays might show a. b. c. d. e. A left cervical rib A mass in the upper lobe of the right lung Aneurysm of the aortic arch Right pneumothorax Thoracic duct blockage in the posterior mediastinum
  • Block 5 Questions 111 5-45. A 77-year-old man complains to you of an annoying buzzing sound in his right ear that bothers him mostly at night. This is classified as a. b. c. d. e. Conductive deafness Sensorineural deafness Central deafness Tinnitus Presbycusis 5-46. Jill and Tom have been neighbors and close friends their whole lives. They are both 13 years old and are in the same eighth grade class. Jill has begun to notice and talk about a few of the ninth grade boys and she spends less time with Tom. Tom is upset and feels hurt and inferior. The most likely cause of this situation is that a. b. c. d. Other boys are beginning to notice Jill Jill’s girlfriends are beginning to spend more time with new friends Tom’s physical development is slower than Jill’s Jill’s cognitive and social development has made her more interested in her girlfriends e. Tom’s physical development has made him show more interest in competitive sports 5-47. A 6-year-old girl presents to the clinic with scaly patches on the scalp. Primary smears and culture of the skin and hair were negative. A few weeks later, she returned and was found to have inflammatory lesions. The hair fluoresced under Wood’s light and primary smears of skin and hair contained septate hyphae. On speaking with the parents, it was discovered that there were several pets in the household. Which of the following is the most likely agent? a. b. c. d. e. Microsporum audouinii Microsporum canis Trichophyton tonsurans Trichophyton rubrum Epidermophyton floccosum
  • 112 Clinical Vignettes for the USMLE Step 1 5-48. A 54-year-old male presents with several problems involving his face and pain in his shoulder. He states that he has smoked 2 packs of cigarettes a day for almost 40 years. Physical examination reveals ptosis of his left upper eyelid, constriction of his left pupil, and lack of sweating (anhidrosis) on the left side of his face. No other neurologic abnormalities are found. This individual most likely has a. b. c. d. e. A bronchioloalveolar carcinoma involving the left upper lobe A small cell carcinoma involving the hilum of his left lung A squamous cell carcinoma involving the left mainstem bronchus An adenocarcinoma involving the apex of his left lung An endobronchial carcinoid tumor involving the right mainstem bronchus 5-49. An 18-year-old male high school baseball player gets hit in the head with a fastball in the temporal area. He does not lose consciousness, but afterward develops a slight headache. He is not taken to the emergency room. By evening he develops severe headache with vomiting and confusion. At that time he is taken to the emergency room, where, after being examined by a neurosurgeon, he is taken to the operating room for immediate surgery for an epidural hematoma. Which one of the following is most likely present in this individual? a. b. c. d. e. Transection of a branch of the middle meningeal artery Bleeding from torn bridging veins Rupture of a preexisting berry aneurysm Rupture of an arteriovenous malformation Cortical bleeding occurring opposite the point of a traumatic injury 5-50. After a mild hemorrhage, compensatory responses initiated by the baroreceptor reflex keeps blood pressure at or close to its normal value. Which one of the following values is less after compensation for the hemorrhage than it was before the hemorrhage? a. b. c. d. e. Venous compliance Heart rate Ventricular contractility Total peripheral resistance Coronary blood flow
  • BLOCK 6 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • BLOCK 6 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Questions 6-1. A college student received an injury as a result of being tackled in a football game. After the game, the student was treated at a local hospital and was found to be unable to abduct and rotate the left arm at the shoulder, flex the elbow, and extend the wrist of the left side. Upon further examination, testing revealed depression of the biceps reflex of this limb, but the reflex activity involving the other limbs was normal. The most likely site of the injury is a. b. c. d. e. Precentral gyrus Basilar pons Ventral horn cells at C1 Nerve roots of C5-C6 Triceps muscle 115
  • 116 Clinical Vignettes for the USMLE Step 1 6-2. An elderly, somewhat obese man is brought to the emergency room complaining of sudden spontaneous flailing movements of his right arm and leg. The arm movements particularly were most severe proximally. No other neurologic deficits were noted. The patient had most likely suffered a hemorrhage in a. b. c. d. e. The cerebellum The ventral horn of the spinal cord The hypothalamus Primary sensory cortex The subthalamic nucleus 6-3. A 32-year-old man is admitted with a bleeding ulcer. This is his fifth episode of bleeding from gastric ulcers and he also has moderate diarrhea. Each time, his ulcers have been difficult to resolve. Which neoplastic lesion is most likely to be found in this man? a. b. c. d. e. Small cell carcinoma of the lung Gastric adenocarcinoma Small intestinal carcinoid Prostate adenocarcinoma Gastrinoma 6-4. A 2-day-old neonate becomes lethargic and uninterested in breastfeeding. Physical examination reveals tachypnea (rapid breathing) with a normal heartbeat and breath sounds. Initial blood chemistry values include normal glucose, sodium, potassium, chloride, and bicarbonate (HCO3−) levels; initial blood gas values reveal a pH of 7.53, partial pressure of oxygen (PO2) normal at 103 mmHg, and partial pressure of carbon dioxide (PCO2) decreased at 27 mmHg. Which of the following treatment strategies is indicated? a. b. c. d. e. Administer alkali to treat metabolic acidosis Administer alkali to treat respiratory acidosis Decrease the respiratory rate to treat metabolic acidosis Decrease the respiratory rate to treat respiratory alkalosis Administer acid to treat metabolic alkalosis
  • Block 6 Questions 117 6-5. The first child of a couple has trisomy 21 (not the result of mosaicism), and they come to you wanting to know the risk of having another child with Down’s syndrome. The mother’s age is 23, and the father’s age is 25. Both appear normal and neither have had any unusual diseases. You analyze their karyotypes and find that the father’s karyotype is normal, but the mother has a Robertsonian translocation involving chromosome 21 (21q21q). Which one of the listed percentages is the best estimate of the chance that the next living child of this couple will have Down’s syndrome? a. b. c. d. e. 0% 15% 33% 50% 100% 6-6. Lethargy, malaise, and fatigue are observed in a patient 2 weeks after eating raw hamburger at a restaurant. The most likely infectious cause is a. b. c. d. e. Toxoplasma Cytomegalovirus E. coli Salmonella Clostridium 6-7. A man presents with a wide-based, ataxic gait during his attempts at walking. He also is unsteady and sways when standing and displays a tendency to fall backward or to either side in a drunken manner. A lesion is most likely located in the a. b. c. d. e. Hemispheres of the posterior cerebellar lobe Anterior limb of the internal capsule Dentate nucleus Anterior lobe of the cerebellum Flocculonodular lobe of the cerebellum
  • 118 Clinical Vignettes for the USMLE Step 1 6-8. A 55-year-old postmenopausal female develops weakness, polyuria, and polydipsia. Nephrocalcinosis is detected by a computed tomography (CT) scan. Her serum creatinine is elevated. Which of the following agents may have caused these adverse effects? a. b. c. d. e. Estrogens Prednisone PTU Etidronate Vitamin D 6-9. A patient with jaundice complains of RUQ pain. Liver function tests show a bilirubin of 3.0 mg/dL, alkaline phosphatase about four times normal and both AST and ALT increased about 50% above normal. The best imaging test to order first in evaluating this patient would be a. b. c. d. e. Ultrasound Abdominal CT scan Abdominal MRI Barium swallow KUB (flat-plate x-ray of the abdomen) 6-10. A patient with symptoms of urinary tract infection had a culture taken, which grew 5 × 103 E. coli. The laboratory reported it as “insignificant.” The most clinically appropriate action is a. Do no further clinical workup b. Suggest to the laboratory that low colony counts may reflect infection c. Determine if fluorescent microscopy is available for the diagnosis of actinomycosis d. Consider vancomycin as an alternative drug e. Suggest a repeat antibiotic susceptibility test
  • Block 6 Questions 119 6-11. A 4-year-old girl presents in the clinic with megaloblastic anemia and failure to thrive. Blood chemistries reveal orotic aciduria. Enzyme measurements of white blood cells reveal a deficiency of the pyrimidine biosynthesis enzyme orotate phosphoribosyltransferase and abnormally high activity of the enzyme aspartate transcarbamoylase. Which one of the following treatments will reverse all symptoms if carried out chronically? a. b. c. d. e. Blood transfusion White blood cell transfusion Dietary supplements of phosphoribosylpyrophosphate (PRPP) Oral thymidine Oral uridine 6-12. A lumbar puncture is performed on a patient with headaches, photophobia, clouding of consciousness, and neck stiffness. If these symptoms are the result of bacterial infection of the meninges, then what would examination of the cerebrospinal fluid (CSF) most likely reveal? a. b. c. d. e. Pressure Increased Increased Increased Decreased Increased Gross Appearance Cloudy Clear Clear Clear Clear Protein Increased Increased Increased Decreased Increased Glucose Decreased Normal Normal Normal Normal Inflammation Neutrophils Lymphocytes Mononuclear cells Lymphocytes Mixed
  • 120 Clinical Vignettes for the USMLE Step 1 Questions 6-13 through 6-14 A 67-year-old woman slipped on a throw-rug and fell with her right arm extended in an attempt to ease the impact of the fall. She experienced immediate severe pain in the region of the right collar bone and in the right wrist. Painful movement of the right arm was minimized by holding the arm close to the body and by supporting the elbow with the left hand. 6-13. There is marked tenderness and some swelling in the region of the clavicle about one-third of the distance from the sternum. The examiner can feel the projecting edges of the clavicular fragments. The radiograph confirms the fracture and shows elevation of the proximal fragment with depression and subluxation (underriding) of the distal fragment. Traction by which of the following muscles causes subluxation (the distal fragment underrides the proximal fragment)? a. b. c. d. e. Deltoid muscle Pectoralis major muscle Pectoralis minor muscle Sternomastoid muscle Trapezius muscle 6-14. Internal bleeding can be a complication if the subluxed bone fragment tears a vessel and punctures the pleura. Which of the following vascular structures is particularly vulnerable in a clavicular fracture? a. b. c. d. e. Axillary artery Brachiocephalic artery Lateral thoracic artery Subclavian artery Thoracoacromial trunk
  • Block 6 Questions 121 6-15. A 21-year-old man was bitten by a tick in Oregon. Two years later, during the course of routine screening for an unknown ailment, a screening Lyme disease test was performed, which was negative. A Western blot strip (IgG) showed the following pattern: Which of the following is the correct interpretation of the test? a. b. c. d. e. The patient has acute Lyme disease The patient has chronic Lyme disease The pattern may represent nonspecific reactivity The screening test should be repeated The patient should be tested for HIV on the basis of the Western blot 6-16. A 24-year-old female presents after having several “attacks” that last for about 24 h. She states that during these attacks she develops nausea, vomiting, vertigo, and ringing in her ears. Physical examination reveals a sensorineural hearing loss. The pathology of her condition involves a. b. c. d. Acute suppurative inflammation Dilation of the cochlear duct and saccule A cyst of the middle ear filled with keratin A tumor of the middle ear composed of lobules of cells in a highly vascular stroma e. New bone formation around the stapes and the oval window
  • 122 Clinical Vignettes for the USMLE Step 1 6-17. A 27-year-old female is diagnosed with hypercortisolism. To determine whether cortisol production is independent of the pituitary gland, you decide to suppress ACTH production by giving a high-potency glucocorticoid. Which glucocorticoid is the best for this indication? a. b. c. d. e. Triamcinolone Prednisone Hydrocortisone Dexamethasone Methylprednisolone 6-18. A patient with a peptic ulcer was admitted to the hospital and a gastric biopsy was performed. The tissue was cultured on chocolate agar incubated in a microaerophilic environment at 37°C for 5 to 7 days. At 5 days of incubation, colonies appeared on the plate and were curved, Gramnegative rods, oxidase-positive. The most likely identity of this organism is a. b. c. d. e. Campylobacter jejuni Vibrio parahaemolyticus Haemophilus influenzae Helicobacter pylori Campylobacter fetus 6-19. A 62-year-old male alcoholic is brought into the emergency room acting very confused. Physical examination reveals a thin and emaciated male who has problems with memory, ataxia, and paralysis of his extraocular muscles. Extensive workup reveals atrophy and small hemorrhages in the periventricular region of his brain and around the mamillary bodies. These signs and symptoms are most consistent with a deficiency of a. b. c. d. e. Biotin Riboflavin Selenium Pyridoxine Thiamine
  • Block 6 Questions 123 6-20. A 45-year-old female being treated for a chronic UTI develops acute alcohol intolerance. Which of the following agents could have caused this intolerance? a. b. c. d. e. Cefoperazone Amoxicillin Sulfamethoxazole-trimethoprim Norfloxacin Tetracycline 6-21. A man known to be an alcoholic for at least 15 years presents with fever, elevated serum bilirubin, elevated WBC count, and an AST/ALT ratio greater than 2. A liver biopsy shows Mallory bodies, WBCs, and degenerating cells. You should tell this patient that the biopsy findings are a. Consistent with cirrhosis b. Essentially normal c. Consistent with alcoholic hepatitis that may revert to normal if he stops drinking alcohol d. Consistent with alcoholic hepatitis that will progress to cirrhosis e. Not interpretable because of the presence of degenerating cells and it will need to be repeated 6-22. You have been asked to evaluate a 62-year-old man for a possible early dementia. The initial interview with the patient is not remarkable. The most common presenting feature of Alzheimer’s disease that you should now focus your diagnostic evaluation on is a. b. c. d. e. Change in personality Loss of memory Difficulty in learning new information Impairment of orientation to time Loss of intellectual skills 6-23. A 60-year-old female treated for breast cancer develops leukopenia and severe stomatitis and oral ulcerations. Which of the following agents most likely caused these findings? a. b. c. d. e. 5-FU Paclitaxel Cyclophosphamide Tamoxifen Carboplatin
  • 124 Clinical Vignettes for the USMLE Step 1 6-24. When a patient is asked to follow an object when it is placed in the right side of his visual field, he is unable to move his right eye either up or down. The lesion is most likely situated in the a. b. c. d. e. Medulla Basilar aspect of the pons Pontine tegmentum Midbrain Cerebellum 6-25. A man with chills, fever, and headache is thought to have “atypical” pneumonia. History reveals that he raises chickens and that approximately 2 weeks ago he lost a large number of them to an undiagnosed disease. The most likely diagnosis of this man’s condition is a. b. c. d. e. Anthrax Q fever Relapsing fever Leptospirosis Ornithosis (psittacosis)
  • Block 6 Questions 125 YOU SHOULD HAVE COMPLETED APPROXIMATELY 25 QUESTIONS AND HAVE 30 MINUTES REMAINING. 6-26. A patient is found to have internal (medially directed) strabismus of the left eye, paralysis of the muscles of facial expression on the left side, hyperacusis (louder perception of sounds) of the left ear, and loss of taste from the anterior two-thirds of the tongue on the left. The mouth is somewhat drier than normal. In addition, in the left eye there is a lack of tearing, and a blink reflex cannot be elicited from the stimulation of either the right or the left cornea. There is accompanying upper motor neuron paralysis of the right side of the body. Internal strabismus (deviation of the eye medially) results from paralysis of which of the following cranial nerves? a. b. c. d. e. Cranial nerve II Cranial nerve III Cranial nerve IV Cranial nerve V Cranial nerve VI
  • 126 Clinical Vignettes for the USMLE Step 1 6-27. A 44-year-old obese male has a significantly high level of plasma triglycerides. Following treatment with one of the following agents, his plasma triglyceride levels decrease to almost normal. Which agent did he receive? a. b. c. d. Neomycin Lovastatin Cholestyramine Gemfibrozil 6-28. A 55-year-old man begins to be emotionally labile, tense, hyperexcitable. He has recently had difficulty with his job. He has lost 20 lbs in weight. He is distractable, has a short attention span, and has impaired recent memory. Your initial workup reveals a fine tremor of the hands, and laboratory work suggests an endocrine abnormality. What is the most likely diagnosis? a. b. c. d. e. Hypoparathyroidism Hyperthyroidism Hyperparathyroidism Hypothyroidism Addison’s disease 6-29. A 65-year-old man is diagnosed with a form of a peripheral neuropathy. This individual will likely display a. b. c. d. e. A loss in motor function, but sensory functions will remain largely intact A reduction in conduction velocity of the affected nerve An increase in the number of Ranvier’s nodes Degeneration of myelin but the axon will typically remain intact Signs of an upper motor neuron (UMN) paralysis 6-30. A patient in heart failure improves markedly after using a drug that increases the inotropic state of her heart. Which one of the following changes is primarily responsible for the improvement in her condition? a. b. c. d. e. A reduction in heart rate A reduction in heart size An increase in end-diastolic pressure An increase in wall thickness An increase in cardiac excitability
  • Block 6 Questions 127 6-31. A young girl has had repeated infections with Candida albicans and respiratory viruses since the time she was 3 months old. As part of the clinical evaluation of her immune status, her responses to routine immunization procedures should be tested. In this evaluation, the use of which of the following vaccines is contraindicated? a. b. c. d. e. Diphtheria toxoid Bordetella pertussis vaccine Tetanus toxoid BCG Inactivated polio 6-32. A 41-year-old female is seen in the psychiatric clinic for a follow-up appointment. She has been taking an antidepressant for three weeks with some improvement in mood. However, she complains of drowsiness, palpitations, dry mouth, and feeling faint on standing. Which antidepressant is she taking? a. b. c. d. e. Amitriptyline Trazodone Fluoxetine Venlafaxine Bupropion 6-33. A 38-year-old woman with rheumatoid arthritis develops worse joint pain and also pain and paresthesias in scattered locations in both arms and both legs. Her sedimentation rate increases significantly and you diagnose vasculitis causing a. b. c. d. e. Mononeuropathy Brown-Séquard’s syndrome Polyneuropathy Mononeuropathy multiplex Radiculopathy
  • 128 Clinical Vignettes for the USMLE Step 1 6-34. A sputum sample was brought to the laboratory for analysis. Gram stain revealed the following: rare epithelial cells, 8 to 10 polymorphonuclear leukocytes per high-power field, and pleomorphic Gram-negative rods. As the laboratory consultant, which of the following interpretations should you make? a. b. c. d. e. The sputum specimen is too contaminated by saliva to be useful There is no evidence of an inflammatory response The patient has pneumococcal pneumonia The patient has Vincent’s disease The appearance of the sputum is suggestive of Haemophilus pneumonia 6-35. A 55-year-old female with painful chronic diarrhea, multiple recurrent duodenal ulcers, and increased basal gastric acid output is most likely to have a. b. c. d. e. A gastrin-secreting tumor of the pancreas A serotonin-secreting tumor of the ileum A somatostatin-secreting tumor of the duodenum An epinephrine-secreting tumor of the adrenal medulla An erythropoietin-secreting tumor of the liver 6-36. A middle-aged man presents with congestive heart failure with elevated liver enzymes. His skin has a grayish pigmentation. The levels of liver enzymes are higher than those usually seen in congestive heart failure, suggesting an inflammatory process (hepatitis) with scarring (cirrhosis) of the liver. A liver biopsy discloses a marked increase in iron storage. In humans, molecular iron (Fe) is a. b. c. d. e. Stored primarily in the spleen Stored in combination with ferritin Excreted in the urine as Fe++ Absorbed in the intestine by albumin Absorbed in the ferric (Fe+++) form
  • Block 6 Questions 129 6-37. A 41-year-old man comes to your office with his wife because she has been unable to conceive with him. He is married for the first time. His wife has two children by her previous marriage. The patient is well with no risk factors for heart disease. As a child, he had the usual communicable diseases, including chickenpox and mumps, and as an adult he received the recommended schedule of immunizations. The likely site of his infertility is a. b. c. d. Pretesticular Testicular Posttesticular Idiopathic 6-38. A 65-year-old male with a pneumonia has a sputum culture that is positive for a staphylococcal strain that is β-lactamase-positive. Which is the best choice of penicillin therapy in this patient? a. b. c. d. e. Ampicillin Oxacillin Ticarcillin Penicillin G Carbenicillin
  • 130 Clinical Vignettes for the USMLE Step 1 Questions 6-39 through 6-40 After an individual is admitted to the hospital, it is determined that he displays a variable weakness of cranial nerve and limb muscles but shows no clinical signs of denervation from tests, which include electromyogram (EMG) recordings. This disorder was partially reversed by the administration of drugs that inhibit acetylcholinesterase. 6-39. The individual is likely to be suffering from a. b. c. d. e. Multiple sclerosis (MS) Amyotrophic lateral sclerosis (ALS) Myasthenia gravis Combined system disease Muscular dystrophy (MD) 6-40. The likely basis for this disorder is the result of a. b. c. d. e. The production of excessive quantities of acetylcholine (ACh) The production of antibodies that act against nicotinic ACh receptors A minor stroke involving the motor strip of the cerebral cortex A vitamin B deficiency Viral encephalitis 6-41. A family in which several individuals have arthritis and detached retina is diagnosed with Stickler syndrome. The locus for Stickler syndrome has been mapped near that for type II collagen on chromosome 12, and mutations in the COL2A1 gene have been described in Stickler syndrome. The family became interested in molecular diagnosis to distinguish normal from mildly affected individuals. Which of the results below would be expected in an individual with a promoter mutation at one COL2A1 gene locus? a. Western blotting detects no type II collagen chains b. Southern blotting using intronic restriction sites yields normal restriction fragment sizes c. Reverse transcriptase–polymerase chain reaction (RT-PCR) detects one-half normal amounts of COL2A1 mRNA in affected individuals d. Fluorescent in situ hybridization (FISH) analysis using a COL2A1 probe detects signals on only one chromosome 12 e. DNA sequencing reveals a single nucleotide difference between homologous COL2A1 exons
  • Block 6 Questions 131 6-42. A 53-year-old banker develops paralysis on the right side of the face, which produces an expressionless and drooping appearance. He is unable to close the right eye and also has difficulty chewing and drinking. Examination shows loss of blink reflex in the right eye to stimulation of either right or left conjunctiva. Lacrimation appears normal on the right side, but salivation is diminished and taste is absent on the anterior right side of the tongue. There is no complaint of hyperacusis. Audition and balance appear to be normal. The lesion is located a. In the brain and involves the nucleus of the facial nerve and superior salivatory nucleus b. Within the internal auditory meatus c. At the geniculate ganglion d. In the facial canal just distal to the genu of the facial nerve e. Just proximal to the stylomastoid foramen 6-43. A 21-year-old female presents because her urine has turned a brown color. She states that about 2 months ago her urine turned brown 2 days after a cold and stayed brown for about 3 days. At the current time a urinalysis reveals 2+ blood with red cells and red cell casts. Further laboratory tests include a complete blood count (CBC), serum electrolytes, BUN, creatinine, glucose, antinuclear antibodies (ANAs), and serum complement levels (C3 and C4). All of these tests are within normal limits. Immunofluorescence examination of a renal biopsy from this patient reveals the presence of large, irregular deposits of IgA/C3 in the mesangium. A linear staining pattern is not found. What is the most likely diagnosis for this patient? a. b. c. d. e. Berger’s disease Focal segmental glomerulosclerosis Goodpasture’s disease Lipoid nephrosis Membranoproliferative glomerulonephritis 6-44. A 45-year-old female treated for ovarian cancer develops difficulty hearing. Which of the following agents most likely caused these findings? a. b. c. d. e. Paclitaxel Doxorubicin Bleomycin 5-FU Cisplatin
  • 132 Clinical Vignettes for the USMLE Step 1 6-45. A 36-year-old man presents at his physician’s office complaining of fever and headache. On examination, he had leukopenia and increased liver enzymes, and inclusion bodies were seen in his monocytes. History revealed that he was an outdoorsman and remembered removing a tick from his leg. Which of the following diseases is most likely causing the symptoms described? a. b. c. d. e. Lyme disease Ehrlichiosis Rocky Mountain spotted fever Q fever Tularemia (Francisella tularensis) 6-46. A patient who presents to the hospital with severe headaches develops convulsions and dies. At autopsy the brain grossly has a “Swiss cheese” appearance due to the presence of numerous small cysts containing milky fluid. Microscopically, a scolex with hooklets is found within one of these cysts. What is the causative agent for this disease? a. b. c. d. e. Taenia saginata Taenia solium Diphyllobothrium latum Echinococcus granulosa Toxocara canis 6-47. Previously, you treated a 44-year-old man, a former intravenous drug abuser, for acute hepatitis C infection. Several months later, it is clear that the patient has chronic hepatitis and may need therapy with interferon. Which long-term complications of hepatitis C infection must you discuss so that the patient can make an informed decision about treatment? a. b. c. d. e. Hepatoma and cirrhosis Hepatic adenoma Sclerosing cholangitis Hemochromatosis Lymphoma or leukemia
  • Block 6 Questions 133 6-48. A urologist refers a 20-year-old man because of hypospadias and infertility. He has been sexually active since his early teens. Recently, he married and, despite many attempts, his wife has been unable to become pregnant. The likely site of his infertility is a. b. c. d. Pretesticular Testicular Posttesticular Idiopathic 6-49. A 65-year-old male presents with bradykinesia, tremors at rest, and muscular rigidity. Physical examination reveals the patient to have a “masklike” facies. In this patient, where would intracytoplasmic eosinophilic inclusions most likely be found? a. b. c. d. e. Basal ganglia Caudate nucleus Hippocampus Midbrain Substantia nigra 6-50. A 30-year-old male patient was seen by the emergency service and reported a 2-week history of a penile ulcer. He noted that this ulcer did not hurt. Which one of the following conclusions/actions is most valid? a. b. c. d. e. Draw blood for a herpes antibody test Perform a dark-field examination of the lesion Prescribe acyclovir for primary genital herpes Even if treated, the lesion will remain for months Failure to treat the patient will have no untoward effect, as this is a self-limiting infection
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  • BLOCK 7 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • BLOCK 7 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Questions 7-1. A 17-year-old individual who is phenotypically female presents for workup of primary amenorrhea and is found to have an XY karyotype. The most likely diagnosis is a. b. c. d. e. Androgen insensitivity syndrome Deficiency of 5-α-reductase Kallmann’s syndrome Mixed gonadal dysgenesis Turner’s syndrome 7-2. An ill patient denied being bitten by insects. However, he had spent some time in a milking barn and indicated that it was dusty. Of the following rickettsial diseases, which one has he most likely contracted? a. b. c. d. e. Scrub typhus Rickettsialpox Brill-Zinsser disease Q fever Rocky Mountain spotted fever (RMSF) 137
  • 138 Clinical Vignettes for the USMLE Step 1 7-3. A 75-year-old man was rushed to the hospital from his retirement community when he suddenly became confused and could not speak but could grunt and moan. The patient could follow simple commands and did recognize his wife and children although he could not name them or speak to them. Additional immediate examination revealed weakness of the right upper extremity. Several days later, a more comprehensive examination revealed weakness and paralysis of the right hand and arm with increased biceps and triceps reflexes. Paralysis and weakness were also present on the lower right side of the face. Pain, temperature, and touch modalities were mildly decreased over the right arm, hand, and face, and proprioception was reduced in the right hand. The patient had regained the ability to articulate with great difficulty a few simple words but could not repeat even simple two or three word phrases. Which artery or major branch of a large artery suffered the occlusion that produced the observed symptoms? a. b. c. d. e. Anterior choroidal artery Middle cerebral artery Posterior communicating artery Ophthalmic artery Anterior cerebral artery 7-4. A neurological examination of a 75-year-old male reveals that when the abdominal wall is stroked, the muscles of the abdominal wall of the side of the body stimulated failed to contract. Other neurological tests appeared normal. The likely region affected includes a. b. c. d. e. C1–C5 spinal segments C6–T1 spinal segments T2–T7 spinal segments T8–T12 spinal segments L1–L5 spinal segments
  • Block 7 Questions 139 7-5. A 63-year-old female is hospitalized secondary to markedly decreased vision. She has no history of polydipsia or nocturia. Physical examination finds bilateral sluggish light reflexes and a bitemporal hemianopsia. No papilledema is present, and her urine specific gravity is within normal limits. A CT scan of the head finds a suprasellar mass with calcification. What is the most likely diagnosis for this tumor? a. b. c. d. e. Craniopharyngioma Germinoma Juvenile pilocytic astrocytoma Medulloblastoma Meningioma 7-6. A 55-year-old woman manager of a regional long-distance telephone office whom you examine for the first time feels well. You do a complete physical examination, which is normal except for a few very small palpable and moveable, nontender nodes in both cervical chains and occasional wheezes in the lungs. However, her laboratory studies show the following hepatitis B virus profile: negative HBsAg, positive anti-HBs, low levels of IgG anti-HBc, negative anti-HBeAg, and positive anti-HBe. The most likely diagnosis is a. b. c. d. e. Acute HBV infection, high infectivity Late-acute HBV, low infectivity Recovered from HBV infection Chronic HBV infection, high infectivity Immunization with HBsAg vaccine 7-7. A 75-year-old female in congestive heart failure (CHF) is unable to climb a flight of stairs without experiencing shortness of breath. Digoxin is administered to improve cardiac muscle contractility. Within two weeks, she has a marked improvement in her symptoms. What cellular action of digoxin accounts for this? a. b. c. d. e. Inhibition of cyclic adenosine 5′-monophosphate (cAMP) synthesis Inhibition of mitochondrial calcium (Ca2+) release Inhibition of the sodium (Na+) pump Inhibition of β-adrenergic stimulation Inhibition of adenosine triphosphate (ATP) degradation
  • 140 Clinical Vignettes for the USMLE Step 1 7-8. A 55-year-old man who is being treated for adenocarcinoma of the lung is admitted to a hospital because of a temperature of 38.9°C (102°F), chest pain, and a dry cough. Sputum is collected. Gram’s stain of the sputum is unremarkable and culture reveals many small Gram-negative rods able to grow only on a charcoal yeast extract agar. This organism most likely is a. b. c. d. e. Klebsiella pneumoniae Mycoplasma pneumoniae Legionella pneumophila Chlamydia trachomatis S. aureus
  • Block 7 Questions 141 7-9. A female patient falls on an icy sidewalk and complains of her thumb hurting. You take her x-ray and show her there are no fractures. However, she asks what the small light circles (arrow) on the x-ray are. You explain they are sesamoid bones in the tendon of the a. b. c. d. e. Flexor pollicis longus Flexor pollicis brevis Adductor pollicis Abductor pollicis longus Abductor pollicis brevis
  • 142 Clinical Vignettes for the USMLE Step 1 7-10. A 55-year-old male describes bilateral pain in his lower back and legs with prolonged standing while working on an assembly line. Whenever he sits down and takes a break, he gets some relief, but it recurs when he resumes his job. No other inciting events can be identified. The most likely cause of this problem is a. b. c. d. Degenerative joint disease Degenerative disk disease Peripheral vascular disease Lumbar spinal stenosis 7-11. During an office visit, a 40-year-old female reports that she is awakened in the middle of the night by intense jaw pain and often is gritting or grinding her teeth. Relaxing the jaw does not help ease the pain. She is a very active, social, and energetic person. From your experience with previous patients suffering from temporomandibular disorders, you suspect that the primary causal link is a. b. c. d. e. Muscular fatigue Physical trauma Muscular or joint infection Anxiety or depression Early rheumatoid arthritis 7-12. A 10-month-old, previously healthy male infant develops a severe, watery diarrhea 2 days after visiting the pediatrician for a routine checkup. The most likely diagnosis is a. b. c. d. e. Rotavirus infection Enterotoxigenic E. coli infection Entamoeba histolytica infection Lactase deficiency Ulcerative colitis
  • Block 7 Questions 143 7-13. As a primary care practitioner, a middle-aged patient of yours seeks advice about her aging parents. She is concerned about what to expect in terms of declining cognitive and physiologic function, and in terms of providing for health care. Which of the following statements to her would be accurate? a. Twenty percent of aged persons live in long-stay institutions (nursing homes, mental hospitals, homes for the aged) b. The majority of old people feel bad most of the time c. Aged drivers have more accidents per person than drivers under age 65 d. All five senses tend to decline in old age e. Personality traits become unstable in the elderly 7-14. An individual is diagnosed with retinitis pigmentosa, which produces a defective opsin. This defect will most likely result in a. b. c. d. e. Degeneration of area 17 of the cerebral cortex Degeneration of cone cells Loss of central vision Total loss of vision Reduced response to light 7-15. A term infant is born at home and does well with breast-feeding. Two days later, the mother calls frantically because the baby is bleeding from the umbilical cord and nostrils. The most likely cause is a. b. c. d. Deficiency of vitamin C due to a citrus-poor diet during pregnancy Hypervitaminosis A due to ingestion of beef liver during pregnancy Deficiency of vitamin K because infant intestines are sterile Deficiency of vitamin K because of disseminated intravascular coagulation (disseminated clotting due to infantile sepsis) e. Deficiency of vitamin E due to maternal malabsorption during pregnancy 7-16. A 19-year-old college student develops a rash. She works part-time in a pediatric AIDS clinic. Her blood is drawn and tested for specific antibody to the chickenpox virus (varicella-zoster). Which of the following antibody classes would you expect to find if she is immune to chickenpox? a. b. c. d. e. IgA IgD IgE IgG IgM
  • 144 Clinical Vignettes for the USMLE Step 1 7-17. A husband and wife, both in their mid-thirties, have been patients of yours for over 10 years. In the past, the husband has unsuccessfully been treated for alcohol abuse. The wife has asked that the two of them be seen together to discuss what might be of help with any of their related health problems. In the discussion of individual and family stress, the husband asked if medicine had anything to offer for his condition. As you are explaining the benefits and risks of disulfiram (Antabuse), the wife explains that her husband now drinks even more than before. At this point, the husband becomes angry and shouts, “I don’t need Antabuse, Alcoholics Anonymous, or anything else! I know I may have a drinking problem, but I can handle it myself without anybody’s help!” In the above scenario, the husband is demonstrating a. b. c. d. e. Displacement Denial Projection Rationalization Reaction formation 7-18. A 40-year-old female with duodenal ulcers is treated with a combination of agents that includes clarithromycin. Of the following enzymes, which is inactivated by clarithromycin? a. b. c. d. e. Dihydrofolate reductase Glucose-6-phosphate dehydrogenase Cytochrome P450 Na+,K+-ATPase Na+,K+,Cl− co-transporter
  • Block 7 Questions 145 7-19. A 72-year-old male presents in the Emergency Room with dizziness and nystagmus. Examination reveals a loss of pain and temperature sensation over the right side of the face and the left side of the body. The patient exhibits ataxia and intention tremor on the right in both the upper and lower extremities and is unable to perform either the finger-to-nose or heelto-shin tasks on the right. In addition, he is hoarse and demonstrates pupillary constriction and drooping of the eyelid on the right. Finally, the right side of his face is drier than the left. Following vascular blockage, necrotic damage in which of the following would explain the patient’s hoarseness? a. b. c. d. e. Nucleus ambiguus Lateral spinothalamic tract Spinal nucleus of CN V Descending sympathetic pathways Inferior cerebellar peduncle 7-20. You are running a community health clinic in a rural area where the patient population is mainly of low socioeconomic status. You would expect that the illness that is least likely to occur in higher rates than the general population is a. b. c. d. e. Iatrogenic illness Chronic illness Obesity Hypertension Coronary artery disease 7-21. A 38-year-old male with AIDS presents with decreasing mental status. The workup at this time includes a spinal tap. Cerebrospinal fluid (CSF) is stained with a mucicarmine stain and india ink. The mucicarmine stain reveals numerous yeasts that stain bright red. The india ink prep reveals through negative staining that these yeasts have a capsule. What is the most likely diagnosis? a. b. c. d. e. Chromomycosis Coccidioidomycosis Cryptococcosis Cryptosporidiosis Paracoccidioidomycosis
  • 146 Clinical Vignettes for the USMLE Step 1 7-22. A 59-year-old male with a history of rheumatic heart disease is found to have atrial fibrillation (AF), for which he is treated with digoxin. Treatment with digoxin converts his AF to a normal sinus rhythm and most likely results in a decrease in which of the following? a. b. c. d. The length of the refractory period The velocity of shortening of the cardiac muscle The conduction velocity in the atrioventricular (AV) node The atrial maximum diastolic resting potential 7-23. A patient with neurological problems has an elevated cerebrospinal fluid (CSF) antibody titer to measles virus. You would most likely suspect a. b. c. d. e. Fifth disease Susceptibility to chickenpox Possible subacute sclerosing panencephalitis (SSPE) Possible hepatitis B infection Acute Lyme disease 7-24. A 54-year-old male alcoholic presents with the sudden onset of severe, constant epigastric pain that radiates to his midback. Further evaluation finds fever, steatorrhea, and discoloration around his flank and umbilicus. Laboratory tests find elevated serum levels of amylase and lipase. What is the most likely cause of these findings? a. b. c. d. e. Acute appendicitis Acute cholangitis Acute cholecystitis Acute diverticulitis Acute pancreatitis 7-25. A person is told that he has astigmatism. To correct this defect, the optometrist prescribes a a. b. c. d. e. Cylindrical lens because the cornea or lens is oblong Concave lens because the eyeball is too long Convex lens because the lens is too short Neutral lens because the eyeball is normal but the cornea is too thin Concave lens because the cornea is opaque
  • Block 7 Questions 147 YOU SHOULD HAVE COMPLETED APPROXIMATELY 25 QUESTIONS AND HAVE 30 MINUTES REMAINING. 7-26. A 60-year-old male develops elevation of blood pressure, hyperglycemia, decreased bone density, and occult blood in his stool. Which of the following agents is associated with these adverse effects? a. b. c. d. e. Hydrochlorothiazide Pamidronate Finasteride Prednisone Metformin 7-27. Postmortem histologic sections are taken from the liver of a 19-yearold female who died from an overdose of acetaminophen. These specimens would most likely reveal a. b. c. d. e. Centrilobular necrosis Focal scattered necrosis Geographic necrosis Midzonal necrosis Periportal necrosis
  • 148 Clinical Vignettes for the USMLE Step 1 7-28. Patients who are extremely allergic to bee stings will self-administer epinephrine when stung. The activation of adrenergic beta-receptors by the injected epinephrine will decrease a. b. c. d. e. The contraction of airway smooth muscle The strength of ventricular muscle contraction The rate of depolarization in the SA node The transport of calcium into skeletal muscle fibers The rate of glycogenolysis in the liver 7-29. A 22-year-old female who requests a postcoital contraceptive after being raped would best be treated with which of the following? a. b. c. d. e. Mifepristone Spironolactone Aminoglutethimide Leuprolide Fludrocortisone 7-30. A child comes to an emergency room because of an infected dog bite. The wound is found to contain small Gram-negative rods. The most likely cause of infection is a. b. c. d. e. E. coli H. influenzae Pasteurella multocida Brucella canis Klebsiella rhinoscleromatis 7-31. A patient suffers from adenosine deaminase (ADA) deficiency, an autosomal recessive immune deficiency in which bone marrow lymphoblasts cannot replicate to generate immunocompetent lymphocytes. The treatment option that would permanently cure the patient is a. Germ-line gene therapy to replace one ADA gene copy b. Germ-line gene therapy to replace both ADA gene copies c. Somatic cell gene therapy to replace one ADA gene copy in circulating lymphocytes d. Somatic cell gene therapy to replace both ADA gene copies in circulating lymphocytes e. Somatic cell gene therapy to replace one ADA gene copy in bone marrow lymphoblasts
  • Block 7 Questions 149 7-32. A 55-year-old woman complains of headaches and is subsequently diagnosed as having a tumor localized to the left parietal lobe. In addition to a variety of sensory deficits, further examination also reveals a reduction in her visual fields. The most likely visual deficit would include a. b. c. d. e. Left homonymous hemianopsia Right homonymous hemianopsia Left upper quadrantanopia Right upper quadrantanopia Right lower quadrantanopia 7-33. You have taken on a part-time responsibility as the company physician for a small factory that has a mixture of hourly workers, engineers, and executives. The company is under stress because of falling profits and competition with foreign manufacturers. You are aware of a number of stresses in the workplace from uncertainty about the future of the company to interpersonal conflict. Which of the following psychological stresses is likely to have the most adverse impact on physical health? a. b. c. d. e. Regressiveness Interpersonal conflict Confusion Uncontrollability Fearfulness 7-34. Radiation treatment for a pituitary tumor in an 8-year-old boy resulted in the complete loss of pituitary function. As a result, the child is likely to experience a. b. c. d. e. Hypothyroidism and goiter Increased ACTH Absent sexual maturation Accelerated growth spurts Increased TSH levels
  • 150 Clinical Vignettes for the USMLE Step 1 7-35. A 40-year-old male suspected of having adrenal insufficiency is treated with a synthetic derivative of cosyntropin to assess adrenocortical activity. Which of the following enzymes is activated by cosyntropin? a. b. c. d. e. f. Adenyl cyclase Mitogen-activated protein kinase Phosphoinositol 3-kinase Acetylcholinesterase (AChE) Phospholipase C Cyclic guanosine 5′-monophosphate (cGMP) phosphodiesterase
  • Block 7 Questions 151 7-36. Your patient just took up jogging in the evening for exercise and complains that after a mile or so his left “leg” begins to hurt. You question him on regions of the body or movements that do or do not evoke pain and find that it is widespread throughout his left lower limb. Based on the location of the constriction of the artery (indicated by the arrow), what compartment or movement would you think would be least affected by the reduced arterial blood flow? a. b. c. d. e. Gluteal region Flexion of the thigh Extension of the leg Posterior thigh Plantar flexion of the foot
  • 152 Clinical Vignettes for the USMLE Step 1 7-37. A couple has three girls, the last of whom is affected with cystic fibrosis. The first-born daughter marries her first cousin—that is, the son of her mother’s sister—and they have a son with cystic fibrosis. The father has a female cousin with cystic fibrosis on his mother’s side. Select the pedigree that best represents this family history from the diagrams below. a. b. c. d. e. f. g. h. Diagram A Diagram B Diagram C Diagram D Diagram E Diagram F Diagram G Diagram H
  • Block 7 Questions 153 7-38. Two days after admission, a 57-year-old man suddenly has a seizure. He was undergoing evaluation for substernal chest pain. The nursing staff noted that he seemed to be a little shaky since shortly after arrival on the floor. He has no history of seizures and a stat CT of the head performed during the postictal state was normal. Laboratory results had shown an MCV of 101 (elevated) and his AST was mildly elevated (one and one-half normal). In this patient, the most likely imbalance that would contribute to this event would be a. b. c. d. e. Folate deficiency Fasting hypoglycemia Hypomagnesemia Thiamine deficiency Vitamin B12 deficiency 7-39. A 30-year-old man comes to your office with complaints of fatigue, anorexia, nausea, and vomiting. He does not have fever. His urine is dark. On physical examination, his liver is slightly enlarged and minimally tender. He does not have edema or spider angiomata. Laboratory tests show the following: negative HBsAg, negative IgM anti-HAV, positive IgM antiHBc, and negative anti-HCV. The most likely diagnosis is a. b. c. d. e. Acute hepatitis A Acute hepatitis B Acute hepatitis A and B Chronic hepatitis B Acute hepatitis C 7-40. A 35-year-old male is diagnosed with primary syphilis. Which of the following agents is the best choice for treating this patient? a. b. c. d. e. A first-generation cephalosporin Oxacillin Imipenen Benzathine penicillin G Vancomycin
  • 154 Clinical Vignettes for the USMLE Step 1 7-41. A patient stung by a bee is rushed into the emergency room with a variety of symptoms including increasing difficulty in breathing due to vasal and bronchial construction. While your subsequent treatment is to block the effects of histamine and other acute-phase reactants released by most cells, you must also block the slow-reacting substance of anaphylaxis (SRS-A), which is the most potent constrictor of the muscles enveloping the bronchial passages. What is SRS-A composed of? a. b. c. d. e. Thromboxanes Interleukins Complement Leukotrienes Prostaglandins 7-42. A 55-year-old man discovered that he had pain in the neck and right arm and weakness in extending his fingers of his right hand with loss of sensation in the right thumb and middle fingers. A neurological examination further revealed a weakness of the right biceps reflex, but other neurological signs could not be detected. The most likely diagnosis of this individual is a. Syringomyelia involving the cervical cord b. A knife wound of the right arm completely severing nerves innervating the biceps muscle c. Prolapse of a cervical disk d. Poliomyelitis involving the cervical cord e. AIDS 7-43. A 37-year-old female with Graves’ disease who requires antithyroid therapy becomes pregnant. Which antithyroid drug is safest? a. b. c. d. Potassium iodide (KI) Methimazole PTU Potassium perchlorate (KClO4)
  • Block 7 Questions 155 7-44. Fever of unknown origin in a farmer who raises goats would most likely be caused by which of the following organisms? a. b. c. d. e. Brucella melitensis Clostridium novyi T. pallidum Histoplasma capsulatum Mycobacterium tuberculosis 7-45. After receiving incompatible blood, a patient develops a transfusion reaction in the form of back pain, fever, shortness of breath, and hematuria. This type of immunologic reaction is classified as a a. b. c. d. e. Systemic anaphylactic reaction Systemic immune complex reaction Delayed type hypersensitivity reaction Complement-mediated cytotoxicity reaction T cell–mediated cytotoxicity reaction 7-46. A 55-year-old man was brought into the hospital with a severe burn to his left hand. The man had placed his hand on the hot burner of an electric stove but had not sensed anything wrong until he smelled burning flesh. Neurologic examination revealed loss of pain and temperature sensation over dermatomes C4 through T6 bilaterally. However, pain and temperature were perceived bilaterally both above C4 and below T6. Discriminative touch was present in unburned dermatomes on the left and in the right extremity. Although the left hand was too damaged to accurately assess muscle function, weakness and wasting of small muscles of the right hand was noted. Muscle strength and reflexes were otherwise normal. Pain and temperature sensations from the extremities ascend in the spinal cord in the a. b. c. d. e. Intermediolateral cell column Cuneate fasciculus Lateral spinothalamic tract Dorsal columns Fasciculus gracilis
  • 156 Clinical Vignettes for the USMLE Step 1 7-47. A man who was stabbed in the back during a fight is brought to the emergency room. On examination you find impaired pain and temperature sensation in one leg and impaired proprioception and vibration sense in the opposite leg. These findings are descriptive of a a. b. c. d. e. Mononeuropathy Brown-Séquard’s syndrome Polyneuropathy Mononeuropathy multiplex Radiculopathy 7-48. A 30-year-old male presents with multiple soft, raised, beefy-red superficial ulcers in his left groin. Physical examination reveals several enlarged left inguinal lymph nodes. A histologic section from an enlarged lymph node that is stained with a silver stain reveals characteristic Donovan bodies within macrophages. What is the most likely diagnosis? a. b. c. d. e. Chancroid Gonorrhea Granuloma inguinale Lymphogranuloma venereum Syphilis 7-49. A 40-year-old patient with a recent viral infection presents with a significantly tender gland, low radioiodine uptake, and signs and symptoms of thyrotoxicosis. This presentation is most likely a. b. c. d. e. Graves’ disease Subacute thyroiditis Toxic multinodular goiter Hashimoto’s thyroiditis Toxic adenoma 7-50. An individual sustained a severe knife wound, damaging a spinal nerve adjoining its entry to the spinal cord. If one could examine this peripheral nerve and its cell body, which of the following events would he or she most likely observe? a. b. c. d. e. A displacement of the nucleus toward the periphery of the cell A mitotic division of the neuronal cell body A more intense staining of the cell body Degeneration of processes along the axon proximal but not distal to the lesion An initial loss of mitochondria in the axoplasm at Ranvier’s node
  • BLOCK 8 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
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  • BLOCK 8 YOU HAVE 60 MINUTES TO COMPLETE 50 QUESTIONS. Questions 8-1. A 20-year-old male has a urethral discharge. Culture of the discharge shows Neisseria gonorrhoeae. Which of the following agents is the best choice for treating this patient? a. b. c. d. e. Ceftriaxone Benzathine penicillin G Imipenen Amikacin Sulfamethoxazole-trimethoprim 159
  • 160 Clinical Vignettes for the USMLE Step 1 8-2. A 27-year-old female presents with headaches, muscle pain (myalgia), anorexia, nausea, and vomiting. She denies any history of drug or alcohol use, but upon further questioning she states that recently she has lost her taste for coffee and cigarettes. Physical examination reveals a slight yellow discoloration of her scleras, while laboratory results indicate a serum bilirubin level of 1.8 mg/dL, and aminotransferases (AST and ALT) levels are increased. These signs and symptoms are most consistent with a diagnosis of a. b. c. d. e. Gilbert’s syndrome Chronic hepatitis Amebic liver abscess Acute viral hepatitis Acute hepatic failure
  • Block 8 Questions 161 8-3. A 22-year-old male who belongs to a weekend football league presents in the ER. He was running with the ball when a defender tackled him in the midthigh. The patient reports that when he got up, his thigh hurt, so he sat out the rest of the game. When walking to the car, his posterior thigh was extremely painful and swollen. After his shower, he noticed it was becoming discolored with increased swelling. You are concerned about the presence of a hematoma and a disruption of the arterial blood flow to the hamstring muscles. An arteriogram is performed and the vessels in question (arrows) show good filling by contrast. These blood vessels are a. b. c. d. e. Descending branches of the inferior gluteal artery Perforating branches of the deep femoral artery Perforating branches from the obturator artery Perforating branches of the femoral artery Posterior femoral artery
  • 162 Clinical Vignettes for the USMLE Step 1 8-4. A routine eye examination reveals the presence of inflammation limited to the left optic disk, probably due to neuritis of this region. The likely visual deficit resulting from this disorder is a. b. c. d. e. Total blindness of the left eye Left homonymous hemianopsia Left heteronymous hemianopsia Left enlargement of the blind spot Left upper quadrantanopia
  • Block 8 Questions 163 8-5. A female infant was born prematurely after rupture of membranes and, within 1 day of birth, developed a fever and died. The pregnant mother had been cultured just prior to the birth of her child and her vaginal culture revealed group B streptococci (S. agalactiae). Which one of the pictured tests shown in the figure below would provide the most rapid and useful information? A C B D a. b. c. d. Test A Test B Test C Test D
  • 164 Clinical Vignettes for the USMLE Step 1 8-6. An elderly woman is seen at your office with a complaint of loss of vision in her left eye, which had been transient on a couple of occasions but is now persisting. She has been seen recently at urgent care centers for multiple complaints including generalized fatigue, left-sided dull boring headaches with occasional sharp jabbing sensations, and arthritic complaint in the hips. In addition, she reports some recent loss of 7 to 10 pounds. The only remarkable finding on the routine labs obtained from her prior evaluations is an elevated alkaline phosphatase. You determine that the likely cause of her condition is a. b. c. d. Glaucoma Brain tumor arising anterior to the optic chiasm Optic neuritis Temporal arteritis 8-7. A 30-year-old alcoholic with no apparent liver disease has decided to abstain from alcohol. Shortly thereafter, he becomes agitated, anxious, has visual hallucinations, is generally totally disoriented, and suffers bouts of insomnia. Which of the following agents might be of use in averting these findings? a. b. c. d. e. f. g. h. i. j. k. Primidone Disulfiram Dextroamphetamine Valproic acid Phenylephrine Phenytoin Isoetharine Carbamazepine Amitriptyline Triazolam Diazepam
  • Block 8 Questions 165 8-8. A 28-year-old man is treated in an emergency room for a superficial gash on his forehead. The wound is bleeding profusely, but examination reveals no fracture. While the wound is being sutured, he relates that while he was using an electric razor, he remembers becoming dizzy and then waking up on the floor with blood everywhere. The physician suspects a hypersensitive cardiac reflex. The patient’s epicranial aponeurosis (galea aponeurotica) is penetrated, which results in severe gaping of the wound. The structure overlying the epicranial aponeurosis is a. b. c. d. e. A layer containing blood vessels Bone The dura mater The periosteum (pericranium) The tendon of the epicranial muscles (occipitofrontalis) 8-9. A 3-month-old boy presents with poor feeding and growth, low muscle tone (hypotonia), elevation of blood lactic acid (lactic acidemia), and mild acidosis (blood pH 7.3 to 7.35). The ratio of pyruvate to lactate in serum is elevated, and there is decreased conversion of pyruvate to acetyl coenzyme A in fibroblasts. Which of the following compounds might be considered for therapy? a. b. c. d. e. Pyridoxine Thiamine Free fatty acids Biotin Ascorbic acid 8-10. A 60-year-old woman was hospitalized with a severe respiratory infection for several weeks. Afterward, she displayed symptoms of myalgia and weakness of the lower limbs. In addition, she also showed loss of muscle tone and some flaccidity with loss of tendon reflexes. Examination also revealed a weakness of facial muscles. This constellation of symptoms progressed for approximately 2 weeks and persisted for more than a year, at which time, recovery took place at a slow rate. There was also some demyelination coupled with lymphatic inflammation at the site of demyelination. The most likely cause of this patient’s condition is a. b. c. d. e. Myasthenia gravis Muscular dystrophy (MD) Multiple sclerosis (MS) Guillain-Barré syndrome Lumbar disk prolapse
  • 166 Clinical Vignettes for the USMLE Step 1 8-11. A 45-year-old male takes simvastatin for hypercholesterolemia; however, his cholesterol level remains above target at maximal doses. Cholestyramine is added to the therapeutic regimen. What drug-drug interaction can occur? a. b. c. d. The combination will not lower cholesterol more than either agent alone The combination causes elevated very-low-density lipoprotein (VLDL) Cholestyramine inhibits gastrointestinal (GI) absorption of simvastatin Simvastatin is a direct antagonist of cholestyramine 8-12. A 52-year-old mother of three is at the stage of life when all three children are moving away from home in pursuit of education and careers. Sociological studies have shown that women who have launched their last children most often report a. b. c. d. e. A less meaningful existence More feelings of depression Less positive self-concepts Less stress Fewer social activities 8-13. A 4-year-old African boy develops a rapidly enlarging mass that involves the right side of his face. Biopsies of this lesion reveal a prominent “starry sky” pattern produced by proliferating small, noncleaved malignant lymphocytes. Based on this microscopic appearance, the diagnosis of Burkitt’s lymphoma is made. This neoplasm is associated with chromosomal translocations that involve a. b. c. d. e. bcl-2 c-abl c-myc erb-B N-myc 8-14. A 47-year-old male is seen in the medicine clinic with recently diagnosed mixed hyperlipidemia. An antihyperlipidemic is administered that favorably affects levels of VLDL, low-density lipoprotein (LDL), and highdensity lipoprotein (HDL) and inhibits cholesterol synthesis. This drug is: a. b. c. d. e. Lovastatin Colestipol Niacin Probucol Neomycin
  • Block 8 Questions 167 8-15. A pediatric patient treated for grand mal seizures develops abnormal values on liver function tests. Which of the following antiepileptic agents would cause this to occur? a. b. c. d. e. Carbamezine Valproic acid Phenytoin Phenobarbital Gabapentin 8-16. A 45-year-old man presents for frontal bossing and enlarged nose, tongue, and jaw. He has doughy palms and spadelike fingers. The best screening test to establish the diagnosis is a. b. c. d. e. Random growth hormone Insulin-like growth factor type 1 (IGF-1) TSH Prolactin Fasting blood sugar 8-17. A 45-year-old woman is hospitalized for a cholecystectomy. She appears to be anxious and worried about the surgery. Which type or types of information provided to the patient will be most effective in reducing stress? a. b. c. d. e. Sensory information Procedural information Coping information Sensory and procedural information Sensory and coping information 8-18. A 36-year-old female with a chronic UTI treated with ciprofloxacin is not responsive to the antibiotic. Which of the following agents that she might have been taking for other reasons would decrease the effectiveness of ciprofloxacin? a. b. c. d. e. An antacid An antihistamine A nonsteroidal anti-inflammatory An anxiolytic A multivitamin not containing iron
  • 168 Clinical Vignettes for the USMLE Step 1 8-19. A box of ham sandwiches with mayonnaise prepared by a person with a boil on his neck was left out of the refrigerator for the on-call interns. Three doctors became violently ill approximately 2 h after eating the sandwiches. The most likely cause is a. b. c. d. e. S. aureus enterotoxin Coagulase from S. aureus in the ham S. aureus leukocidin C. perfringens toxin Penicillinase given to inactivate penicillin in the pork 8-20. A 33-year-old patient with an average menstrual cycle of 28 days comes in for a routine Pap smear. It has been 35 days since the start of her last menstrual period, and a vaginal smear reveals clumps of basophilic cells. As her physician, you suspect a. b. c. d. e. She will begin menstruating in a few days She will ovulate within a few days Her serum progesterone levels are very low There are detectable levels of hCG in her serum and urine She is undergoing menopause 8-21. A culture of bacteria not resistant to tetracycline develops an infection from a virus that is derived from the lysis of tetracycline-resistant bacteria. Most of the bacterial progeny of the original culture is found to have become resistant to tetracycline. What phenomenon has occurred? a. b. c. d. e. Conjugation Colinearity Recombination Transformation Transduction
  • Block 8 Questions 169 8-22. A 38-year-old woman is referred to a neurologist because she complained of visual loss and muscle weakness. Subsequent examination revealed additional signs: impairment of other sensations, which included tingling and burning sensations; weakness of the lower limbs; paralysis of the upper limbs; progressive impairment of gait; signs of UMN involvement (i.e., spasticity and increased tendon reflexes); and bladder disturbances. No signs of infection were detected as measured by blood analysis, cultures, and chest x-ray. However, elevations in CSF protein were noted as well an abnormal IgG synthesis. Consequently, the neurologist’s diagnosis of the patient was that she was suffering from a. b. c. d. e. Diffuse cerebellar degeneration ALS Multiple sclerosis MS A peripheral neuropathy A prefrontal cortical brain tumor 8-23. An individual comes upon an automobile accident in which someone is injured, but does not appear to be in a life-threatening situation. Of the following factors that would determine whether the individual would avoid taking action or volunteer to help, which would be likely to influence the individual to avoid taking action? a. b. c. d. e. Perception that the other person is intoxicated Proximity to the other person Knowledge of what to do Few others in the immediate area Male gender of bystander 8-24. A 65-year-old woman is seen for evaluation of dementia. On examination, you note that her left pupil does not react well to light. When she follows your finger with her eyes, as you approach the bridge of her nose, you note the left pupil to constrict equally as well as the right one. The most important test to order at this point would be a. b. c. d. e. Titer for Lyme disease B12 level RPR HIV Fasting glucose
  • 170 Clinical Vignettes for the USMLE Step 1 8-25. A male patient is brought to the emergency department (ED) following ingestion of an unknown substance. He is found to have an elevated temperature, hot and flushed skin, dilated pupils, and tachycardia. Of the following, which would most likely cause these findings? a. b. c. d. e. Propranolol Methylphenidate Prazosin Guanethidine Atropine
  • Block 8 Questions 171 YOU SHOULD HAVE COMPLETED APPROXIMATELY 25 QUESTIONS AND HAVE 30 MINUTES REMAINING. 8-26. An immigrant from eastern Europe is rushed into the emergency room with nausea, vomiting, diarrhea, and abdominal pain. His family indicates he has eaten wild mushrooms. They have brought a bag of fresh, uncooked mushrooms from a batch he had not yet prepared. You note the presence of Amanita phalloides, the death-cap mushroom. A liver biopsy indicates massive hepatic necrosis. Care is supportive. A major toxin of the death-cap mushroom is the hepatotoxic octapeptide α-amanitin, which inhibits a. b. c. d. e. DNA primase RNA nuclease DNA ligase RNA polymerase RNA/DNA endonuclease
  • 172 Clinical Vignettes for the USMLE Step 1 8-27. A 38-year-old male presents with right lower quadrant abdominal pain, fever, and a peripheral neutrophilia. An emergency appendectomy is performed, but the appendix is found to be grossly unremarkable. Instead, the lymph nodes surrounding the appendix are found to be enlarged, inflamed, and matted together. Which one of the listed organisms is the most likely cause of these abnormalities? a. b. c. d. e. Enteropathic Escherichia coli Enterobius vermicularis Trichomonas hominis Yersinia enterocolitica Bacillus anthracis 8-28. A 36-year-old male unemployed dishwasher with no history of seizures presents with difficulty thinking coherently and claims that he is an astronaut. Following treatment, he suddenly has a grand mal seizure. Which neuroleptic agent was administered? a. b. c. d. e. Haloperidol Fluphenazine Clozapine Molindone Loxapine 8-29. An immigrant family from rural Mexico brings their 3-month-old child to the emergency room because of whistling inspiration (stridor) and high fever. The child’s physician is perplexed because the throat examination shows a gray membrane almost occluding the larynx. A senior physician recognizes diphtheria, now rare in immunized populations. The child is intubated, antitoxin is administered, and antibiotic therapy is initiated. Diphtheria toxin is often lethal in unimmunized persons because it a. Inhibits initiation of protein synthesis by preventing the binding of GTP to the 40S ribosomal subunit b. Binds to the signal recognition particle receptor on the cytoplasmic face of the endoplasmic reticulum receptor c. Shuts off signal peptidase d. Blocks elongation of proteins by inactivating elongation factor 2 (EF-2, or translocase) e. Causes deletions of amino acid by speeding up the movement of peptidyl-tRNA from the A site to the P site
  • Block 8 Questions 173 Questions 8-30 through 8-32 A 56-year-old woman experiences a loss of taste affecting the front of her tongue and the ability to smile as a result of an infection. 8-30. If the sensory loss involves damage of cell bodies, the specific group of neurons so affected would be the a. b. c. d. e. Otic ganglion Nodose (inferior) ganglion Pterygopalatine ganglion Geniculate ganglion Trigeminal ganglion 8-31. The cranial nerve most immediately affected is a. b. c. d. e. Nerve V Nerve VI Nerve VII Nerve IX Nerve X 8-32. The components of the nerve that is affected include a. b. c. d. e. General somatic afferent and general somatic efferent Special visceral afferent and special visceral efferent General visceral afferent and general somatic efferent General somatic afferent and general visceral efferent Special visceral afferent and general visceral efferent 8-33. In a presurgical patient, the great saphenous vein was cannulated in the vicinity of the ankle. During the procedure, the patient experienced severe pain that radiated along the medial border of the foot. Which of the following nerves was accidentally included in a ligature during this procedure? a. b. c. d. e. Medial femoral cutaneous nerve Saphenous nerve Superficial fibular nerve Sural cutaneous nerve Tibial nerve
  • 174 Clinical Vignettes for the USMLE Step 1 8-34. A farming couple in Northern Michigan consult their physician about severe skin rashes and ulcers noted over the past year. They also have lost many cattle over the past year, and claim that their cattle feed changed in consistency and smell about 1 year ago. Chemical analysis of the feed shows high concentrations of polychlorinated biphenyls, a fertilizer related to known carcinogens. The physician sends the chemical to a laboratory for carcinogen testing, which is performed initially and rapidly by a. Inoculation of the chemical into nude mice b. Incubation of mutant bacteria with the chemical to measure the rate of reverse or “back” mutations c. Incubation with stimulated white blood cells to measure the impact on DNA replication d. Computer modeling based on the structures of related carcinogens e. Incubation with mammalian cell cultures to measure the rates of malignant transformation 8-35. A 35-year-old woman comes to your office complaining of weakness in her limbs and fatigability of her muscles, which, it seems to her, lessens after she rests. Sometimes she does not have any muscle weakness, for months at a time, and then she does; all this has been happening to her for the past few years. She tells you that what bothers her most is the “droopiness” of her eyelids. Which one procedure provides definitive confirmation of the diagnosis? a. b. c. d. e. Single-fiber electromyography CT scan or MRI of the head Antiacetylcholine receptor radioimmunoassay Edrophonium chloride test Electroencephalogram (EEG) 8-36. A 45-year-old male with alcoholic cirrhosis is seen in the ED because of a laceration of the scalp. Of the following local anesthetics, which would potentially be toxic? a. b. c. d. Lidocaine Benzocaine Procaine Tetracaine
  • Block 8 Questions 175 8-37. A 34-year-old male patient visits a physician with complaints of fatigue, weight loss, night sweats, and “swollen glands.” The physician also observes that he has an oral yeast infection. An HIV ELISA test is performed. The figure below demonstrates a Western blot for HIV. Based on these results, and assuming a repeatedly reactive ELISA HIV screening test, your best course of action is to a. b. c. d. e. Repeat the test immediately Inform the patient that the test is falsely positive Wait 6 weeks and repeat the test Consider anti-HIV therapy Order an HIV RNA test 8-38. After recovering from a viral respiratory tract infection, a 23-yearold female presents with weakness in her distal extremities that rapidly ascends to involve proximal muscles. Physical examination reveals absent deep tendon reflexes, and a lumbar puncture reveals the CSF protein to be increased, but very few cells are present. A biopsy of a peripheral nerve reveals inflammation and demyelination (radiculoneuropathy). What is the best diagnosis? a. b. c. d. e. Brown-Séquard’s syndrome Charcot-Marie-Tooth disease Diabetes mellitus Guillain-Barré syndrome Syringomyelia
  • 176 Clinical Vignettes for the USMLE Step 1 8-39. During the physical examination of a newborn child, it was observed that the genitalia were female, but masculinized. The genotype was determined to be 46,XX. Which of the following would be the most likely cause of this condition? a. b. c. d. e. Androgen insensitivity Decreased blood ACTH levels Atrophy of the zona reticularis A defect in the cortisol pathway Hypersecretion of vasopressin 8-40. Parents of an adolescent male who have been in your primary care practice consult you with regard to their concern about their son’s behavior. He has been truant from school and has engaged in several pranks with friends that damaged the property of others. They ask about what might predict delinquency in their son. Adolescent delinquency in boys can be predicted most accurately on the basis of a. b. c. d. e. IQ Physique or body type Family size Socioeconomic status of parents Relationship with parents 8-41. You confirm acromegaly in a 58-year-old woman, and a MRI of the pituitary shows a microadenoma. The best choice for treatment is a. b. c. d. e. Transsphenoidal surgery Medical therapy with somatostatin agonist Irradiation Medical therapy with bromocriptine Transfrontal surgery 8-42. A 60-year-old male alcoholic treated for type II diabetes mellitus develops lactic acidosis. Which of the following oral hypoglycemic agents might cause this adverse effect? a. b. c. d. e. Glyburide Metformin Acarbose Rosiglitazone Chlorpropamide
  • Block 8 Questions 177 8-43. A 70-year-old male is admitted to the emergency room and a subsequent MRI reveals the presence of a tumor involving parts of the left temporal lobe. In addition to certain short-term memory deficits, visual deficits are noted as well. The most likely deficits will include a. b. c. d. e. Left homonymous hemianopsia Right homonymous hemianopsia Left upper quadrantanopia Right upper quadrantanopia Left lower quadrantanopia 8-44. It was determined that 95% of an oral 80-mg dose of verapamil was absorbed in a 70-kg test subject. However, because of extensive biotransformation during its first pass through the portal circulation, the bioavailability of verapamil was only 25%. Assuming a liver blood flow of 1500 mL/min, the hepatic clearance of verapamil in this situation was a. b. c. d. e. 60 mL/min 375 mL/min 740 mL/min 1110 mL/min 1425 mL/min 8-45. A 70-year-old female patient was readmitted to a local hospital with fever and chills following cardiac surgery at a major teaching institution. Blood cultures were taken and a Gram-positive coccus grew from the blood cultures within 24 hours. Initial tests indicated that this isolate was resistant to penicillin. Further testing revealed that the isolate possessed the group D antigen, was not β-lactamase-positive, but was resistant to vancomycin. The most likely identification of this isolate is a. b. c. d. e. Enterococcus faecalis Enterococcus durans Enterococcus cassiflavus S. pneumoniae Enterococcus faecium
  • 178 Clinical Vignettes for the USMLE Step 1 8-46. A young child is brought into the hospital emergency room because he has episodes of vomiting, headaches, problems in acquisition of motor skills, cranial nerve dysfunction, and problems in breathing. This combination of syndromes most closely relates to which of the following disorders? a. b. c. d. e. Cleft palate Hydrocephalus Anencephaly Syringomyelia Congenital aneurysm 8-47. A 5-year-old girl is brought in with severe vomiting that has developed suddenly 5 days after she has had a viral infection. Upon questioning, her parents indicate that she was given aspirin for several days to treat a fever that occurred with the viral illness. She is hospitalized and quickly develops signs of cerebral edema. Liver tissue reveals marked steatosis. What is the most likely diagnosis? a. b. c. d. e. α1 antitrypsin deficiency Dubin-Johnson syndrome Hepatitis D infection Reye’s syndrome Wilson’s disease 8-48. Periodic hyperkalemic paralysis is characterized by high potassium concentration and muscle weakness. Which of the following is likely to cause muscle weakness as a result of increased extracellular potassium concentration? a. b. c. d. e. Hyperpolarization of muscle cells Inactivation of sodium channels in muscle cells Increased release of neurotransmitters from alpha motoneurons Decreased potassium conductance in muscle cells Increased duration of action potentials produced by alpha motoneurons
  • Block 8 Questions 179 8-49. A patient delays initiation of movement, displays an uneven trajectory in moving her hand from above her head to touch her nose, and is uneven in her attempts to demonstrate rapid alternation of pronating and supernating movements of the hand and forearm. She probably has a lesion in the a. b. c. d. e. Hemispheres of the posterior cerebellar lobe Flocculonodular lobe of the cerebellum Vermal region of the anterior cerebellar lobe Fastigial nucleus Ventral spinocerebellar tract 8-50. A 19-year-old man living in New Mexico presents to a local clinic after a 1-day history of fever, myalgia, chills, headache, and malaise. He complains of vomiting, diarrhea, abdominal pain, tachypnea, and a productive cough. His white cell count is elevated with an increase in the number of bands. Atypical lymphocytes are also found in the peripheral blood. He is treated with antibiotics, but the next day he develops acute respiratory failure with cardiopulmonary arrest and dies. Postmortem examination of the lungs reveals intraalveolar edema, rare hyaline membranes, and a few interstitial lymphoid aggregates. The most likely cause of this patient’s illness is infection with a. b. c. d. e. Ebola virus Dengue fever virus Hantavirus Yellow fever virus Alphavirus
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  • BLOCK 1 Answers 1-1. The answer is e. (Murray, 5/e, pp 128–129.) Because the boy received his booster within the last 2 years, his level of immunity should be adequate. If an individual has no history of immunization, both antitoxin (passive immunization with tetanus immune globulin) for temporary and fast protection and toxoid (toxin detoxified with formaldehyde) for future and long-lasting protection should be given at different sites. 1-2. The answer is b. (Cotran, pp 1186–1187. Rubin, pp 1291–1292.) Basal cell carcinoma, arising from the pluripotential cells in the basal layer of the epidermis, is the most common tumor in patients with pale skin. This carcinoma is locally invasive and may be quite destructive. Metastasis, however, is quite rare. The classic clinical appearance is a pearly papule with raised margins and a central ulcer. Variants, which are not infrequent, include the superficial type (which may be multifocal), the morphea-like type (which has marked fibrosis and is difficult to eradicate locally), and the pigmented type (which may be mistaken clinically for malignant melanoma). Histologically the cells are deeply basophilic with palisading at the periphery of groups of tumor cells and peritumoral clefting. Abundant eosinophilic cytoplasm may be seen in squamous cell carcinomas, not basal cell carcinomas. 1-3. The answer is b. (Simon, pp 138–145.) Calcification of the internal carotid artery could serve to disrupt nerve fibers proximal to it. One such group of fibers includes parts of the optic nerve. In this case, the component of the right optic nerve affected includes the lateral aspect, or those fibers that mediate vision associated with the nasal visual field of the right eye. If the damage were more extensive and if it involved the entire nerve, then total blindness of the right eye would have occurred. 1-4. The answer is c. (Ryan, pp 552–554.) HIV RT PCR, a nucleic acid amplification test for HIV RNA, has recently been shown to be the most 181 Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  • 182 Clinical Vignettes for the USMLE Step 1 valuable test for a) monitoring a patient’s progress during triple drug therapy and b) determining the chances of progression to AIDS. A viral load of 750,000 copies per ml significantly increases the chance of progression to AIDS within 5 years. The other tests listed do not accurately predict progression to AIDS. The figure below shows the basic structure of HIV including the enzyme, reverse transcriptase. The location of the envelope glycoproteins (gp120 and gp124) is shown, as are the major viral core proteins (p25, p17, p9, and p7).The core protein, p17, is found outside the viral nucleoid and forms the matrix of the virion. RT indicates reverse transcriptase. 1-5. The answer is b. (Alberts, pp 734–749. Cotran, pp 92–93, 343–344.) Many extracellular substances cause intracellular actions via secondmessenger systems. These second messengers may bind to receptors that are located either on the surface of the cell or within the cell itself. Substances that react with intracellular receptors are lipid-soluble (lipophilic) molecules that can pass through the lipid plasma membrane. Examples of these lipophilic substances include thyroid hormones, steroid hormones, and the fat-soluble vitamins A and D. Once inside the cell these substances generally travel to the nucleus and bind to the hormone response element (HRE) of DNA.
  • Block 1 Answers 183 Some substances that react with cell surface receptors bind to guaninenucleotide regulatory proteins. These proteins, called G proteins, may be classified into four categories, namely Gs, Gi, Gt, and Gq. Two of these receptors, Gs and Gi, regulate the intracellular concentration of cyclic adenosine 5′-monophosphate (cAMP). In contrast, Gt regulates the intracytoplasmic levels of cyclic guanosine 5′-monophosphate (cGMP), and Gq regulates the intracytoplasmic levels of calcium ions. Gs and Gi regulate intracellular cAMP levels by their actions on adenyl cyclase, an enzyme located on the inner surface of the plasma membrane that catalyzes the formation of cAMP from ATP. The adenylate cyclase G protein complex is composed of the following components: the receptor, the catalytic enzyme (i.e., adenyl cyclase), and a coupling unit. The coupling unit consists of GTP-dependent regulatory proteins (G proteins), which may either be stimulatory (Gs) or inhibitory (Gi). When bound to GTP and active, Gs stimulates adenyl cyclase and increases cAMP levels. (Gs can be thought of as the “on switch.”) In contrast, when bound to GTP and active, Gi inhibits adenyl cyclase and decreases cAMP levels. (Gi can be thought of as the “off switch.”) It is important to note that cholera toxin and pertussis toxin both act by altering this adenyl cyclase pathway. Cholera toxin inhibits the conversion of Gs-GTP to Gs-GDP. In contrast, pertussis toxin inhibits the activation of Gi-GDP to Gi-GTP. Therefore, both cholera toxin and pertussis toxin prolong the functioning of adenyl cyclase and therefore increase intracellular cAMP, but their mechanisms are different. Cholera toxin keeps the “on switch” in the “on” position, while pertussis toxin keeps the “off switch” in the “off” position. 1-6. The answer is c. (Hardman, p 1183. Katzung, p 819.) Fluconazole penetrates into cerebrospinal fluid, where it is active against Cryptococcus neoformans. When it is given orally, blood levels are almost as high as when it is given parenterally. Amphotericin is administered intravenously and does not appear to be highly effective in fungal meningitis even when administered intrathecally. 1-7. The answer is b. (Howard, pp 253–254.) Oxacillin- and methicillinresistant S. aureus (MRSA) has been rapidly increasing in incidence. MRSA and methicillin-sensitive S. aureus (MSSA) coexist in heterologous populations. Treatment of a patient harboring this heterologous population may provide a selective environment for the MRSA. Prior to changing therapy,
  • 184 Clinical Vignettes for the USMLE Step 1 the susceptibility of the isolate should be determined. Vancomycin has often been used effectively for MRSA, but it is expensive and nephrotoxic. There is no evidence that MRSA is any more virulent or invasive than susceptible strains. 1-8 through 1-10. The answers are 1-8 d, 1-9 a, 1-10 d. (Afifi, pp 133–135. Kandel, pp 972–975.) Specialized peripheral receptors, which specifically respond to changes in blood pressure, include the carotid sinus (associated with cranial nerve IX) and the aortic arch (associated with cranial nerve X). If these receptors (or the cell bodies associated with these receptors) are damaged, then one of the fundamental regulatory mechanisms for the control of blood pressure would be disrupted. The results of such a disruption would likely lead to increases and instability in blood pressure with evidence of spiking of blood pressure. Because these sensory receptors in these structures respond to increases in blood pressure, they are, in effect, stretch receptors and are consequently referred to as baroreceptors. The principal projection of the axons associated with these baroreceptors is the solitary nucleus of the medulla, which in turn, projects to autonomic nuclei such as the dorsal motor nucleus of the vagus nerve, ventrolateral medulla, and higher regions associated with autonomic functions, which include the PAG, hypothalamus, and limbic system. 1-11. The answer is a. ( Junqueira, pp 318–319, 323, 324. Braunwald, pp 1715–1720.) Commonly, initial low levels of glucuronyl (glucuronysl) transferase in the underdeveloped smooth endoplasmic reticulum of hepatocytes in the newborn result in jaundice (neonatal unconjugated hyperbilirubinemia); less commonly, this enzyme is genetically lacking. The neonatal small intestinal epithelium also has an increased capacity for absorption of unconjugated bilirubin, which contributes to the elevated serum levels. Bilirubin, a product of iron-free heme, is liberated during the destruction of old erythrocytes by the mononuclear macrophages of the spleen and, to a lesser extent, of the liver and bone marrow. The hepatic portal system brings splenic bilirubin to the liver, where it is made soluble for excretion by conjugation with glucuronic acid. Increased plasma levels of bilirubin (hyperbilirubinemia) result from increased bilirubin turnover, impaired uptake of bilirubin, or decreased conjugation of bilirubin. Increased bilirubin turnover occurs in Dubin-Johnson and Rotor syn-
  • Block 1 Answers 185 dromes, in which there is impairment of the transfer and excretion of bilirubin glucuronide into the bile canaliculi. In Gilbert’s syndrome, there is impaired uptake of bilirubin into the hepatocyte and a defect in glucuronyl transferase. In Crigler-Najjar syndrome, a defect in glucuronyl transferase occurs in the neonate. The ability of mature hepatocytes to take up and conjugate bilirubin may be exceeded by abnormal increases in erythrocyte destruction (hemolytic jaundice) or by hepatocellular damage (functional jaundice), such as in hepatitis. Finally, obstruction of the duct system between the liver and duodenum (usually of the common bile duct in the adult and rarely from aplasia of the duct system in infants) results in a backup of bilirubin (obstructive jaundice). 1-12. The answer is a. (Hardman, p 1146.) The “red man” syndrome is associated with vancomycin, thought to be caused by histamine release. Prevention consists of a slower infusion rate and pretreatment with antihistamines. 1-13. The answer is a. (Baum, pp 179–183.) J. K. Kiecolt-Glaser and B. A. Esterling both reported studies of the changes that occur in the immune systems of caregivers who have been under the constant stress of caring for a family member with Alzheimer’s disease for many months (average 33 months). A battery of immunologic assessments found that the caregivers had suppressed immune systems; cellular immune system control of latent viruses was poorer than that of a matched control group, the percentage of T lymphocytes was lower, and the helper/suppressor ratio was smaller. The data suggest that chronic and, at times, severe stress can cause persistent changes in immunity. Furthermore, these changes can occur in several components of immunosurveillance. In a study of residents living near Three Mile Island, Baum reported that even six years after the nuclear accident, long-term stress resulted in negative changes in the residents’ immune systems. This finding was indicated by poor cellular control over latent viruses, higher numbers of circulating neutrophils, and lower numbers of B cells and cytotoxic T lymphocytes in the residents. Thus, stress has a direct psychophysiologic effect on immunity. Some bodily changes, such as increased levels of cortisol, can actually destroy immune tissue. Stress also can change physiologic systems and may result
  • 186 Clinical Vignettes for the USMLE Step 1 in increased drug use, smoking, and alcohol use, which can contribute to negative chronic effects on the immune system. There is some evidence that adaptation to stress can occur, but this doesn’t appear to happen in more severe cases such as the caretakers of patients with Alzheimer’s disease. 1-14. The answer is e. (Henry, pp 78–79, 657–659.) The differential diagnosis of microcytosis includes β thalassemia (due to a defect in globin chain synthesis) and iron-deficiency anemia. It is important to distinguish between these two disorders because therapy with iron benefits patients with iron-deficiency anemia, but harms patients with thalassemia because these patients are at risk for iron overload. Both thalassemia minor and iron-deficiency anemia are microcytic disorders in which the mean corpuscular hemoglobin is usually found to be reduced. Red blood cell indexes may be useful in differentiating the two disorders because, while the mean corpuscular hemoglobin concentration (MCHC) is often normal or only slightly reduced in association with thalassemia minor, the MCHC is often definitely reduced in association with iron-deficiency anemia. (Both pernicious and folate-deficiency anemias lead to megaloblastic changes in erythrocytes.) The red cell distribution width (RDW) is a measure of variation in the size of the red cells (anisocytosis). The RDW is increased in patients with iron-deficiency anemia, but is normal in patients with β thalassemia. Also unique to the microcytic anemias is the fact that patients with β thalassemia have increased red blood cell counts, while patients with all of the other microcytic anemias have decreased red blood cell counts. This increased red cell count in β thalassemia may be due to the increased hemoglobin F which shifts the oxygen dissociation curve to the left. This in , turn causes an increased release of erythropoietin. Unlike iron-deficiency anemia, β thalassemia begins as a microcytic anemia. In contrast, irondeficiency anemia progresses through several stages. First there is decreased storage iron, which is followed by decreased circulating iron. At this time patients are still not clinically anemic. Next patients develop a normocytic normochromic anemia that transforms into a microcytic normochromic anemia and finally a microcytic hypochromic anemia. 1-15. The answer is b. (Katzung, pp 504–505.) Amoxapine is a heterocyclic antidepressant that has effects on norepinephrine and serotonin uptake. It is useful in psychotic patients who are depressed. The dopamin-
  • Block 1 Answers 187 ergic antagonism caused by amoxapine may lead to the amenorrheagalactorrhea syndrome. 1-16. The answer is b. (Rhoades, pp 380–383, 395–398.) Under normal conditions, the V/Q ratio in both lungs is the same, so that mixed alveolar gas in both lungs has the same PO2 and PCO2. The gas from the normal lung will be approximately normal (PO2 = 100 mmHg, PCO2 = 40 mmHg). While the gas from the occluded lung, which now represents alveolar dead space, will resemble tracheal gas (PO2 = 150 mmHg, PCO2 = 0 mmHg). When the gas from the two lungs mixes, the average alveolar O2 becomes 125 mmHg and the average PCO2 becomes 20 mmHg. 1-17. The answer is a. (Katzung, p 668.) Fetal lung maturation is normally stimulated by cortisol produced in the fetal adrenal gland. When preterm delivery with inadequate maturation of the lungs is anticipated, large doses of glucocorticoid can be given to the mother to speed up the physiologic process. Betamethasone is the preferred agent because it binds to serum proteins to a lesser extent than cortisol and other glucocorticoids, allowing more steroid to cross the placenta. 1-18. The answer is d. (Levinson, pp 271–279.) The advent of triple therapy or a therapeutic “cocktail” has had a marked effect on AIDS patients. The combination of drugs work together as reverse transcriptive inhibitors and a protease inhibitor. Patients improve rapidly, their CD4 lymphocyte counts increase, and their HIV viral load is drastically reduced, often to <50 copies per ml. On the other hand, an untreated HIV-positive patient with a low CD4 and a high viral load a) is at increased risk of opportunistic infection and b) has a much greater chance of developing AIDS than if the viral load was <50,000. The patient is infectious and his HIV antibody screening test will be positive. The high viral load, however, is not a predictor of response to therapy. Many patients with high viral loads do very well on triple therapy, although resistance to one or more of the agents may subsequently occur. A low CD4 count does not predict progression to AIDS but does indicate increased chance of opportunistic infection such as those listed. Kaposi’s sarcoma, which has been linked to herpesvirus type 8, pneumocystis, and mycobacterial disease are three of the most prevalent opportunistic infections. While HIV-positive patients contract pneumococcal pneumonia, they are probably at no more risk than the general popula-
  • 188 Clinical Vignettes for the USMLE Step 1 tion, as protection against pneumococcal disease is linked to the presence of anticapsular antibody. 1-19. The answer is c. (Katzung, pp 827–828.) Famciclovir is active against herpes simplex and varicella zoster viruses. It is activated by a viral kinase to a triphosphate. The triphosphate is a competitive substrate for DNA polymerase. The incorporation of the famciclovir triphosphate into viral DNA results in chain termination. 1-20. The answer is a. (Murray, pp 182–189. Scriver, pp 1521–1552. Sack, pp 121–138. Wilson, pp 287–317.) Cyanide blocks respiration by displacing oxygen from hemoglobin. Oxidative phosphorylation in the mitochondria cannot proceed because cyanide cannot oxidize (remove electrons) from reduced cofactors like NADH. The citric acid cycle is the major pathway for generating ATP and reducing equivalents (NADH, H+) from catabolism of carbohydrates, amino acids, and lipids. Inability to regenerate NAD+ from NADH through mitochondrial oxidative phosphorylation depletes the cell of NAD+ and inhibits the citric acid cycle. Failure to generate ATP by oxidative phosphorylation using NADH from the citric acid cycle depletes the cell of energy and leads to cell and tissue death (organ failure). Enzymes (citrate synthase, aconitase) and intermediates of the citric acid cycle (citrate, acetyl coenzyme A) need only be present in trace amounts because they are not consumed. 1-21. The answer is d. (Ash, pp 32, 33, 231, 233, 322, 327.) Enterobius (pinworm), Ascaris (roundworm), Necator (hookworm), and Trichuris (whipworm) are roundworms, or nematodes. T. saginata (tapeworm), a segmented flatworm, affects the small intestine of humans. Tapeworm segments, called proglottids, appear in the stool of infected persons. 1-22. The answer is a. (Murray, pp 190–198. Scriver, pp 4517–4554. Sack, pp 121–138. Wilson, pp 287–317.) One of the world’s most common enzyme deficiencies is glucose-6-phosphate-dehydrogenase deficiency (305900). This deficiency in erythrocytes is particularly prevalent among African and Mediterranean males. A deficiency in glucose-6-phosphate dehydrogenase blocks the pentose phosphate pathway and NADPH production. Without NADPH to maintain glutathione in its reduced form, erythrocytes have no
  • Block 1 Answers 189 protection from oxidizing agents. This X-linked recessive deficiency is often diagnosed when patients develop hemolytic anemia after receiving oxidizing drugs such as pamaquine or after eating oxidizing substances such as fava beans. 1-23. The answer is a. (Guyton, pp 496–500.) Breathing air with a low partial pressure of oxygen will stimulate the peripheral chemoreceptors which, in turn, will stimulate respiration. The increased alveolar ventilation will decrease the arterial PCO2 to a value below normal (less than 40 mmHg). Although the increased ventilation will increase the arterial PO2, the resulting value will remain below normal for as long as the individual is breathing air with a low partial pressure of oxygen. A lower than normal arterial O2 tension and a normal or greater than normal arterial CO2 tension is usually a sign of a depressed respiratory center. A greater than normal arterial O2 tension and a lower than normal arterial CO2 tension can only occur if the person is breathing air with a greater than normal concentration of oxygen. 1-24. The answer is e. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp 57–84. Wilson, pp 123–148.) Children with chromosome abnormalities often exhibit poor growth (failure to thrive) and developmental delay with an abnormal facial appearance. This baby is too young for developmental assessment, but the catlike cry should provoke suspicion of cri-du-chat syndrome. Cri-du-chat syndrome is caused by deletion of the terminal short arm of chromosome 5 [46,XX,del(5p), also abbreviated as 5p−] as depicted in panel e. When a partial deletion or duplication like this one is found, the parents must be karyotyped to determine if one carries a balanced reciprocal translocation. The other karyotypes show (a) deletion of the short arm of chromosome 4 [46,XY,del(4p) or 4p−]; (b) XYY syndrome (47,XYY); (c) deletion of the long arm of chromosome 13 [46,XX,del(13q) or 13q−]; (d) Klinefelter’s syndrome (47,XXY). Most disorders involving excess or deficient chromosome material produce a characteristic and recognizable phenotype (e.g., Down’s, cri-du-chat, or Turner’s syndrome). The deletion of 4p− (panel A) produces a pattern of abnormalities (syndrome) known as Wolf-Hirschhorn syndrome; deletion of 13q− produces a 13q− syndrome (no eponym). The mechanism(s) by which imbalanced chromosome material produces a distinctive phenotype is completely unknown.
  • 190 Clinical Vignettes for the USMLE Step 1 1-25. The answer is e. (Cotran, pp 1164–1166.) Tumors of the adrenal medulla include pheochromocytomas, ganglioneuromas, and neuroblastomas. Pheochromocytomas are composed of cells that contain membranebound, dense-core neurosecretory granules and have high cytoplasmic levels of catecholamines. Secretion of these catecholamines produces the characteristic symptoms associated with pheochromocytomas, such as hypertension, palpitations, tachycardia, sweating, and glucose intolerance (diabetes mellitus). Pheochromocytomas are associated with the urinary excretion of catecholamines or their metabolic breakdown products. The catecholamines include dopamine, norepinephrine, and epinephrine. These catecholamines are broken down by two enzymes, catecholamine orthomethyltransferase (COMT) and monoamine oxidase (MAO), into homovanillic acid, normetanephrine, metanephrine, or vanillylmandelic acid (VMA). Any of these metabolic products may be found in the urine of patients with pheochromocytomas; however, VMA is most common. The best screening tests are 24-h urinary metanephrine and VMA levels. Pheochromocytomas have been called the “10% tumor” as 10% are malignant, 10% are multiple (bilateral), 10% are extraadrenal, 10% calcify, and 10% are familial. These familial tumors are associated with neurofibromatosis, MEN 2A, or MEN 2B. 1-26. The answer is c. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp 97–158. Wilson, pp 23–39.) Males always transmit their single X chromosome to their daughters. Therefore, a daughter of a male affected with an X-linked disorder is an obligate carrier for that disorder. When the condition is X-linked recessive, as with most forms of color-blindness, the daughter is unlikely to show any phenotypic evidence that she is carrying this abnormal gene. Offspring of female carriers are of four types: (1) female carrier with one normal and one mutant allele, (2) normal female with two normal alleles, (3) affected male with a single mutant allele, and (4) normal male with a single normal allele. The chance of having an affected child is thus 1/4 or 25%. If the obligate carrier female gives birth to a son, the chance of the son being color-blind is 50%. 1-27. The answer is e. (Katzung, pp 428–429.) Although a rare occurrence, halothane and other inhaled gas anesthetics may cause malignant hyperthermia. Apparently, this occurs in genetically susceptible individuals. Its onset may be accelerated by the concomitant use of succinylcholine. Immediate treatment includes administration of dantrolene.
  • Block 1 Answers 191 1-28. The answer is c. (Levinson, p 313.) Acanthamoeba is a free-living ameba as is Naegleria. Naegleria usually causes severe, often fatal, meningoencephalitis, while Acanthamoeba is uncommonly isolated from contact lens fluid and patients with retinitis who do not store their lenses under sterile conditions. Acanthamoeba can be grown on nonnutrient agar plates using Escherichia coli as a food source. They are identified microscopically with use of a nonspecific fluorescent stain. 1-29. The answer is d. (Carlson, pp 259–267.) Most of the human research on sleep has found that after a few days of sleep deprivation people report perceptual distortions or, in a few cases, even hallucinations. These studies have documented statements such as “the floor seems wavy” or “steam seems to be rising from the floor,” indicating that sleep deprivation affects cerebral functioning. Another research finding is that being sleepy is distinctly different from being tired, as after exercise. Sleepiness can occur even without any activity and sleep deprivation does not appear to interfere with the ability to perform physical exercise. Likewise, there is no evidence of a physiologic stress response to sleep deprivation, indicated by little change in blood levels of cortisol and epinephrine. Sleep does appear to be necessary for the brain to function normally. After a period of sleep deprivation a rebound phenomenon does occur. The individual will sleep longer and spend a much greater time in REM sleep, but will not regain the number of sleepless hours lost. 1-30. The answer is d. (Murray, pp 258–284. Scriver, pp 2863–2914. Sack, pp 205–222. Wilson, pp 361–391.) This man has familial hypercholesterolemia (143890), an autosomal dominant phenotype defined by studying men who experienced heart attacks at young ages. Mutations in the LDL receptor lead to decreased cellular cholesterol uptake and increased serum cholesterol. Since LDL has a high cholesterol content, the LDL fraction is elevated compared to the HDL fraction on lipoprotein electrophoresis. In normal individuals, the LDL is taken up by its specific receptor and imported via caveolae to the cell interior. Cholesterol then produces feedback inhibition on the rate-limiting enzyme of cholesterol synthesis (hydroxymethylglutaryl CoA reductase) and also leads to a decrease in the number of LDL receptors. In rare cases, two individuals with familial hypercholesterolemia marry and produce a child with homozygous familial hypercholesterolemia. These children develop severe atherosclerosis and xanthomas (fatty tumors) at an early age.
  • 192 Clinical Vignettes for the USMLE Step 1 1-31. The answer is e. (Raoult, pp 619–628.) Koplik’s spots are pathognomonic for measles. The measles virus is a paramyxovirus. In industrialized countries, vaccination has reduced the importance of this childhood infection (although U.S. incidence increased in 1989 and 1990). In developing countries, however, measles is a major killer of young children. In America, most states now require proof of immunity before school enrollment, and this has reduced the incidence of disease. 1-32. The answer is e. (Katzung, pp 744, 748.) Vitamin D3 is hydroxylated to 25-OHD3 (calcifediol). Calcifediol is then hydroxylated in the kidney to the most active form of vitamin D, which is 1,25-dihydroxyvitamin D (calcitriol). Calcitriol has a rapid onset of action and a short half-life. The administration of calcitriol causes the elevation of serum Ca levels by enhancing the intestinal absorption of Ca. Calcitriol is indicated in vitamin D deficiency, particularly in patients with chronic renal failure or renal tubular disease, hypoparathyroidism, osteomalacia, and rickets. Serum phosphate levels usually increase with prolonged treatment. 1-33. The answer is a. (Cotran, pp 1148–1151. Chandrasoma, pp 857– 863.) Hyperparathyroidism is caused by excess production of parathyroid hormone (PTH). In patients with hyperparathyroidism, it is important to distinguish primary hyperparathyroidism from secondary hyperparathyroidism. Both forms may be associated with the development of bone lesions, but excess PTH production in primary hyperparathyroidism leads to different laboratory values than those seen with secondary hyperparathyroidism. Increased levels of PTH in primary hyperparathyroidism result in increased serum calcium (hypercalcemia) and decreased serum phosphorus. The serum calcium levels are elevated because of increased bone resorption and increased intestinal calcium absorption, the result of increased activity of vitamin D. PTH also increases calcium reabsorption in the distal renal tubule, but, because the filtered load of calcium exceeds the ability for reabsorption, calcium is increased in the urine (hypercalciuria). PTH also increases urinary excretion of phosphate. The excess calcium in the urine predisposes to renal stone formation, especially calcium oxalate or calcium phosphate stones. Urinary stones can produce flank pain and hematuria. This is the most common presentation for patients with hyperparathyroidism. The hypercalcemia of hyperparathyroidism may also cause peptic ulcer disease due to the stimulation of gastrin release and increased
  • Block 1 Answers 193 acid secretion from the parietal cells. The hypercalcemia also results in muscle weakness, fatigue, and hypomotility of the GI tract, which can lead to constipation and nausea. Alterations of mental status are also common. In contrast to primary hyperparathyroidism, secondary hyperparathyroidism results from hypocalcemia. This causes secondary hypersecretion of PTH and produces the combination of hypocalcemia and increased PTH production. It is primarily found in patients with chronic renal failure. Patients with hypoparathyroidism develop hypocalcemia and hyperphosphatemia but have normal serum creatinine levels. Primary hypoparathyroidism and pseudohypoparathyroidism also result in decreased 24-h excretion of calcium and phosphate. 1-34. The answer is d. (Moore & Dalley, pp 669–670, 810.) The large arrows indicate the proximal humeral epiphyseal plate. The young girl was only 11 and still growing. The epiphyseal plates show up on x-rays as radiolucent cartilage and should not be confused with a fracture. The epiphysis is located at the anatomic neck of the humerus but is not discoid-shaped like many epiphyseal plates in long bones. This plate is tent-shaped, which is why it is not clearly visible all the way across the proximal humerus. 1-35. The answer is b. (Murray, pp 190–198. Scriver, pp 1553–1588. Sack, pp 121–138. Wilson, pp 287–317.) Lactose in breast milk and infant formula is converted by intestinal lactase to glucose and galactose that are efficiently absorbed. In galactosemia (230400), deficiency of galactose-1phosphate uridyl transferase prevents the conversion of galactose into glucose-6-phosphate by the liver or erythrocytes. Most other organs do not metabolize galactose. The severe symptoms of galactosemia are caused by the reduction of galactose to galactitol (dulcitol) in the presence of the enzyme aldose reductase. High levels of galactitol cause cataracts, the accumulation of galactose-1-phosphate contributes to liver disease, and the accumulation of galactose metabolites in urine can be measured as reducing substances by the Clinitest method. Any carbohydrate, including glucose, with a C1 aldehyde registers as a reducing substance by Clinitest, so a Dextrostix (glucose only) test is often performed as a control. In normal children, galactose is first phosphorylated by ATP to produce galactose-1-phosphate in the presence of galactokinase. Next, galactose-1-phosphate uridyl transferase transfers UDP from UDPglucose to form UDP-galactose and glucose-1-phosphate. Under the
  • 194 Clinical Vignettes for the USMLE Step 1 action of UDP-galactose-4-epimerase, UDP-galactose is epimerized to UDP-glucose. Finally, glucose-1-phosphate is isomerized to glucose-6phosphate by phosphoglucomutase. Infants with suspected galactosemia (230400) must be withdrawn from breast-feeding or lactose formulas and placed on nonlactose formulas such as Isomil. 1-36. The answer is b. (Katzung, pp 493–494.) A decrease in thyroid function occurs in most patients on lithium. This effect is usually reversible or not progressive, but a few patients develop symptoms of hypothyroidism. A serum thyroid-stimulating hormone (TSH) concentration is recommended every 6 to 12 months. “Browning” of vision, clinically described as pigmentary retinopathy, occurs with thioridazine. This is due to retinal deposition of the drug. Although neurologic adverse effects (e.g., tremor, choreoathetosis, motor hyperactivity, ataxia, dysarthria, and aphasia) can occur with lithium, it does not cause the neuroleptic malignant syndrome associated with antipsychotic agents. Pseudodepression sometimes occurs in patients on antipsychotics. This may be related to drug-induced akinesia. 1-37. The answer is e. (Cotran, 6/e, pp 70–72.) Certain drugs are important in the control of acute inflammation because they inhibit portions of the metabolic pathways involving arachidonic acid. For example, corticosteroids induce the synthesis of lipocortins, a family of proteins that are inhibitors of phospholipase A2. They decrease the formation of arachidonic acid and its metabolites, prostaglandins and leukotrienes. Aspirin, indomethacin, and other nonsteroidal anti-inflammatory drugs (NSAIDs), in contrast, inhibit cyclooxygenase and therefore inhibit the synthesis of prostaglandins and thromboxanes. The prostaglandins have several important functions. For example, prostaglandin E2 (PGE2), produced within the anterior hypothalamus in response to interleukin 1 secretion from leukocytes, results in fever. Therefore aspirin can be used to treat fever by inhibiting PGE2 production. PGE2 is also a vasodilator that can keep a ductus arteriosus open. At birth, breathing decreases pulmonary resistance and reverses the flow of blood through the ductus arteriosus. The oxygenated blood flowing from the aorta into the ductus inhibits prostaglandin production and closes the ductus arteriosus. Therefore prostaglandin E2 can be given clinically to keep the ductus arteriosus open, while indomethacin can be used to close a patent ductus. Prostaglandin F2 (PGF2) causes uterine contractions, which can result in dysmenorrhea. Indomethacin can be
  • Block 1 Answers 195 used to treat dysmenorrhea by inhibiting the production of PGF2. Bradykinin is a nonapeptide that increases vascular permeability, contracts smooth muscle, dilates blood vessels, and causes pain. It is part of the kinin system and is formed from high-molecular-weight kininogen (HMWK). Histamine, a vasoactive amine that is stored in mast cells, basophils, and platelets, acts on H1 receptors to cause dilation of arterioles and increased vascular permeability of venules. 1-38. The answer is a. (McKenzie, pp 290–291, 393, 394. Junqueira, pp 279, 287–288, 298, 300, 430, 432, 433.) Photomicrographs A and B show two distinctly different types of epithelium: stratified squamous epithelium of the anus (top panel) and crypts (without villi) of the rectum (lower panel). The anus has anal valves and an absence of the muscularis mucosa. The esophageal-cardiac junction also represents a junction between stratified squamous and simple columnar epithelium, but the cardiac portion of the stomach forms the mucus-secreting cardiac glands with no goblet cells. The junction of the stomach (pylorus) and duodenum represents the juncture of two simple columnar epithelia, the pylorus containing the short (compared with fundus) pyloric glands and the duodenum with crypts and villi as well as the submucosal Brunner’s glands. Skin is keratinized. The cervical mucosa contains extensive cervical glands, and the vaginal epithelium is keratinized. In vagina and cervix, the GI tract pattern [epithelium, connective tissue (CT), muscle, CT, muscle, CT] is not present. 1-39. The answer is a. (Murray, pp 190–198. Scriver, pp 1521–1552. Sack, pp 121–138. Wilson, pp 287–317.) Glycosides are formed by condensation of the aldehyde or ketone group of a carbohydrate with a hydroxyl group of another compound. Other linked groups (aglycones) include steroids with hydroxyl groups (e.g., cardiac glycosides such as digitalis or ouabain) or other chemicals (e.g., antibiotics such as steptomycin). Sucrose (α-Dglucose-β-1 → 2-D-fructose), maltose (α-D-glucose-α-1 → 4-D-glucose), and lactose (α-D-galactose-β-1 → 4-D-glucose) are important disaccharides. Fructose is among several carbohydrate groups known as ketoses because it possesses a ketone group. The ketone group is at carbon 2 in fructose, and its alcohol group at carbon 1 (also at carbon 6) allows ketal formation to produce pyranose and furanose rings as with glucose. Most of the fructose found in the diet of North Americans is derived from the disaccharide sucrose (common table sugar). Sucrose is cleaved into equimo-
  • 196 Clinical Vignettes for the USMLE Step 1 lar amounts of glucose and fructose in the small intestine by the action of the pancreatic enzyme sucrase. Deficiency of sucrase can also cause chronic diarrhea. Hereditary fructose intolerance (229600) is caused by deficiency of the liver enzyme aldolase B, which hydrolyzes fructose-1-phosphate. 1-40. The answer is e. (Cotran, p 1129.) The syndrome of inappropriate antidiuretic hormone (SIADH) is an important cause of dilutional hyponatremia that has been identified in tumors of the thymus gland, malignant lymphoma, and pancreatic neoplasms. It occurs predominantly, however, as a result of ectopic secretion of ADH by small cell carcinomas of the lung. Since the tumor cells per se are autonomously producing ADH, there is no feedback inhibition from the hypothalamic osmoreceptors, and the persistent ADH effect on the renal tubules causes water retention even with concentrated urine; hence the term inappropriate ADH. Laboratory findings include low plasma sodium levels (dilutional hyponatremia), low plasma osmolality, and high urine osmolality caused by disproportionate solute excretion without water. 1-41. The answer is a. (Kandel, pp 936–947.) Paradoxical sleep is a term given to REM sleep, which is considered paradoxical because its electroencephalographic pattern resembles that of the alert waking state. Dreaming occurs during REM sleep. When a person is repeatedly awakened during dreaming, a dream deprivation occurs and there is a rebound phenomenon of increased frequency and lengthening of dreaming when the person is permitted to sleep normally. Dream deprivation does not result in a major decrement in psychological or intellectual functions (as does sleep deprivation), but it does appear to retard the memory formation of emotionally toned words. While earlier studies suggested the presence of bizarre behavior, anxiety, irritability, and nightmares, more recent studies have found no such changes in humans even after 16 days of deprivation of dream sleep. 1-42. The answer is c. (Hardman, pp 415–416.) Neuroleptic malignant syndrome is thought to be a severe form of an extrapyramidal syndrome that can occur at any time with any dose of a neuroleptic agent. However, the risk is higher when high-potency agents are used in high doses, especially if given parenterally. Mortality from NMS is greater than 10%. 1-43. The answer is e. (Kumar, pp 395–398. Braunwald, pp 1456–1460. Junqueira, pp 335–336, 344.) The teenage patient is suffering from an asth-
  • Block 1 Answers 197 matic attack, probably allergen-induced. Mast cells are a key player in this airway disease. Mast cells in the bronchioles are stimulated to release histamine and heparin that induce the contraction of smooth bronchiolar muscle and edema in the wall. If the bronchoconstriction is chronic, the long-term result is thickening of the bronchiolar musculature. Other cells involved in asthma include eosinophils, neutrophils, macrophages, and lymphocytes, which signal to each other through a complex cytokine network. Mediators released include bradykinin, leukotrienes, and prostaglandins, which enhance bronchoconstriction, vascular congestion, and edema. The airway epithelium also is involved in response to and release of mediators. These muscle changes are usually accompanied by goblet cell hypersecretion of a viscous mucus, which can obstruct the airway. Eosinophils release proteins that destroy the airway epithelium (releasing Creola bodies). T lymphocytes are also present in more severe “attacks” and, along with B lymphocytes, may play a role in the initiation of allergic asthma. T lymphocytes also release cytokines that activate cell-mediated immunity pathways. Mucociliary transport is active in the trachea and bronchi; alveolar macrophages do not play a role in that process. 1-44. The answer is e. (Murray, pp 48–73. Scriver, pp 2863–2914. Sack, pp 3–17. Wilson, pp 361–370.) Many enzymes interact to regulate blood clotting. Plasmin is activated by proteolytic cleavage of its zymogen, plasminogen. The activating protease is called tissue plasminogen activator (tPA). Plasmin hydrolyzes fibrin clots to form soluble products, and is used to dissolve clots in coronary arteries that cause myocardial infarction. Platelets, thrombin, and fibrinogen promote clotting through the intrinsic pathway and would be contraindicated in myocardial infarction. Platelets form a plug at the site of bleeding and bind prothrombin to facilitate its conversion to thrombin. Fibrinogen is the substrate acted upon by thrombin to yield the fibrin mesh of blood clots. Heparin is a mucopolysaccharide that terminates clot formation by interfering with a number of steps in the coagulation cascade. Heparin inhibits the formation of clots, but cannot dissolve clots that have already formed. 1-45. The answer is e. (Hardman, p 1523.) Administration of intravenous CaG would immediately correct the tetany that might occur in a patient in whom a thyroidectomy was recently performed. Parathyroid hormone would act more slowly but could be given for its future stabilizing effect. Long-term control of a patient after a thyroidectomy can be
  • 198 Clinical Vignettes for the USMLE Step 1 obtained with vitamin D and dietary therapy. Calcitonin is a hypocalcemic antagonist of parathyroid hormone. Plicamycin (mithramycin) is used to treat Paget’s disease and hypercalcemia. The dose employed is about onetenth the amount used for plicamycin’s cytotoxic action. 1-46. The answer is a. (Braunwald, p 1975.) The first choice in testing in this patient is a pregnancy test. If her prolactin level was measured without a pregnancy test, an elevation of prolactin could be wrongly considered primary rather than due to pregnancy. The other tests of LH, estradiol, progesterone are not first choices in the evaluation of amenorrhea. 1-47. The answer is b. (Moore & Dalley, pp 339–341, 418–423.) The indicated line represents the sacroiliac joint. These structures are seen bilaterally between the alae of the sacrum and the ilia. The sacroiliac ligaments might have been sprained by the trauma of the fall. The pathway for spinal nerves is through foramina of the sacrum, not through long bony canals. Similarly, the pathway for the gluteal arteries is through the greater sciatic foramen between the ilium and the sacrum. However, the bones are not contiguous at that level. 1-48. The answer is c. (Hardman, p 527. Katzung, p 516.) Naloxone is a pure opioid antagonist at the µ, κ, and δ receptors. µ-receptor stimulation causes analgesia, euphoria, decreased gastrointestinal (GI) activity, miosis, and respiratory depression. κ-receptor stimulation causes analgesia, dysphoria, and psychotomimetic effects. δ-receptor stimulation is not fully understood in humans, but is associated with analgesia and antinociception for thermal stimuli. 1-49. The answer is b. (Cotran, pp 619–621.) Paroxysmal nocturnal hemoglobinuria (PNH) is an acquired clonal stem cell disorder that is characterized by abnormal red cells, granulocytes, and platelets. The red blood cells (RBCs) are abnormally sensitive to the lytic activity of complement due to a deficiency of glycosyl phosphatidyl inositol (GPI) linked proteins, namely decay-accelerating factor (DAF or CD 55), membrane inhibitor of , reactive lysis (CD55), or CD59 (a C8 binding protein). Complement is normally activated by acidotic states, such as occur with exercise or sleep. In patients with PNH, the acidotic condition that develops during sleep (which is usually at night) causes hemolysis of red blood cells and results
  • Block 1 Answers 199 in red urine in the morning. The erythrocytes of these patients lyse in vitro with acid (Ham’s test) or sucrose (sucrose lysis test). Complications of PNH include the development of frequent thromboses, particularly of the hepatic, portal, or cerebral veins. Since PNH is a clonal stem cell disorder, patients are at an increased risk of developing aplastic anemia or acute leukemia. The autoimmune hemolytic anemias are important causes of acute anemia in a wide variety of clinical states and can be separated into two main types: those secondary to “warm” antibodies and those reactive at cold temperatures. Warm-antibody autoimmune hemolytic anemias react at 37°C in vitro, are composed of IgG, and do not fix complement. They are found in patients with malignant tumors, especially leukemia-lymphoma; with use of such drugs as α-methyldopa; and in the autoimmune diseases, especially lupus erythematosus. Cold-antibody autoimmune hemolytic anemia reacts at 4 to 6°C, fixes complement, is of the IgM type, and is classically associated with Mycoplasma pneumonitis (pleuropneumonia-like organisms). These antibodies are termed cold agglutinins and may reach extremely high titers and cause intravascular red cell agglutination. 1-50. The answer is c. (Sierles, pp 185–187. Ebert, pp 268–270.) Many psychiatric disorders manifest evidence of brain dysfunction. Evidence of such brain dysfunction has been found in 50% or more of patients with schizophrenia. For example, a neurologic examination will demonstrate soft signs (e.g., grasp reflex, rooting reflex, motor impersistence) in 70% of adult schizophrenics; 75% (whether ill or recovered) will also demonstrate abnormalities in eye pursuit; 75% will have moderate-to-severe bilateral impairment on neuropsychological tests; and 50% will have nonspecific abnormalities on the EEG. Also, 50% will have some cortical atrophy and ventricular enlargement on imaging tests. The lactate infusion test induces panic behavior in 80% of patients with panic disorder, but not in patients with schizophrenia.
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  • BLOCK 2 Answers 2-1. The answer is e. (Rhoades, pp 364–368.) Interstitial lung disease is a restrictive-type lung disease in which all the lung volumes, including VC, FRC, and RV, are reduced. The decrease in lung volumes is caused by a decrease in lung compliance. The low compliance produces a high recoil force so that a higher than normal fraction of the forced vital capacity (FEV1/FVC) can be exhaled during expiration. The normal pH is consistent with a normal alveolar ventilation. Because lung compliance is reduced, the normal alveolar ventilation is maintained with a breathing pattern consisting of a high rate and a low volume. 2-2. The answer is c. (Braunwald, p 1984.) The patient has a common presentation for secondary hypogonadism. The large tumor is inhibiting LH secretion with consequently low testosterone secretion. No other pattern fits this clinical presentation. 2-3. The answer is d. ( Moore & Dalley, p 395.) The ischioanal fossa is a fat-filled space that extends from below the levator ani muscle (puborectalis, pubococcygeus, and iliococcygeus muscles). It also extends anteriorly in the area between the pelvic diaphragm (superiorly) and the urogenital diaphragm (inferiorly). It cannot extend superiorly above the pelvic diaphragm and, therefore, cannot extend superiorly anterior to the sacrum. 2-4. The answer is b. (Hardman, p 1062.) Sulfonamides should not be used in pregnant women who are at term because of their ability to cross the placenta and enter the fetus in concentrations sufficient to produce toxic effects. Sulfonamides should also not be given to neonates, especially premature infants, because they compete with bilirubin for serum albumin binding, resulting in increased levels of free bilirubin, which cause kernicterus. 201 Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  • 202 Clinical Vignettes for the USMLE Step 1 2-5. The answer is b. (Cotran, p 1114.) Inflammatory breast carcinoma is often misunderstood because of the qualifying adjective inflammatory. The term does not refer to the presence of inflammatory cells, abscess, or any special histologic type of breast carcinoma; rather, it refers to more of a clinical phenomenon, in that the breast is swollen, erythematous, and indurated and demonstrates a marked increase in warmth. These changes are caused by widespread lymphatic and vascular permeation within the breast itself and in the deep dermis of the overlying skin by breast carcinoma cells. The clinical induration and erythema are presumably related to lymphatic-vascular blockage by tumor cells; if present, these findings mean a worse prognosis. 2-6. The answer is c. (Guyton, pp 269–273.) Sweat normally contains about 40 to 60 meq of sodium per liter of fluid. Thus, approximately 100 meq of sodium will be lost from the extracellular fluid during the exercise period, and when the lost water is replenished, the extracellular fluid will become hypotonic. The hypotonic extracellular fluid will equilibrate with the intracellular fluid and make it hypotonic as well. Because the extracellular fluid volume is dependent on the amount of sodium, the loss of sodium will result in a decreased extracellular fluid volume and an increased intracellular fluid volume after water is replaced. 2-7. The answer is d. (Katzung, pp 704, 942.) Leuprolide is a peptide that is related to GnRH or luteinizing hormone–releasing hormone (LHRH). This agent is used to treat metastatic prostate carcinoma. A hypogonadal state is produced in the patient from the continuous administration of leuprolide, by its capacity to inhibit gonadotropin release. Testosterone levels in the body become significantly reduced. 2-8. The answer is d. (Levinson, pp 243–247.) In a small number of patients with acute hepatitis B infection, HBsAg can never be detected. In others, HBsAg becomes negative before the onset of the disease or before the end of the clinical illness. In such patients with acute hepatitis, hepatitis B virus infection may only be established by the presence of antihepatitis B core IgM (anti-HBc IgM), a rising titer of anti-HBc, or the subsequent appearance of anti-HBsAg. 2-9. The answer is c. (Hardman, p 666.) Inhalation therapy minimizes systemic effects of steroids. Of the agents listed, beclomethasone is the only one delivered by metered-dose inhaler (MDI).
  • Block 2 Answers 203 2-10. The answer is b. (McPhee, p 7.) Duchenne’s muscular dystrophy is an X-linked recessive disorder. The patient’s mother carries one copy of the recessive gene. It is not expressed in the patient’s sisters who may also carry one copy of the recessive gene. Because women possess two X chromosomes, the terms X-linked dominant and X-linked recessive apply only to women. Men, because they possess only one X chromosome, will likely express the full phenotype irrespective of whether the mutation is a dominant or recessive allele in women. 2-11. The answer is c. (Cotran, p 587.) Accumulations of excess fluid within the pericardial cavity are called pericardial effusions. The sudden filling of the pericardial space with fluid is called pericardial tamponade. The three classic signs of pericardial tamponade, called Beck’s triad, include hypotension, elevated jugular pressure, and muffled heart sounds. The latter is due to the damping effect of the pericardial fluid on the heart sounds. Some patients may also demonstrate a decrease in systemic pressure with inspiration, which is called paradoxic pulse. The decrease in cardiac output produces dyspnea, shortness of breath, and hypotension. Decreased atrial filling results in elevated jugular venous pressure. There are several types of pericardial effusions. Serous pericardial effusions are caused most often by congestive heart failure, but they can also be caused by renal disease that produces uremia. Serosanguinous effusions are caused by trauma and cardiopulmonary resuscitation (CPR). Chylous effusions are caused by lymphatic obstruction, while cholesterol effusions are seen in patients with myxedema, which is caused by hypothyroidism. Hemopericardium (blood in the pericardial cavity) is most commonly caused by the rupture of a myocardial infarction. 2-12. The answer is b. (Levinson, pp 218–219.) Adenovirus type 8 is associated with epidemic keratoconjunctivitis, while adenovirus types 3 and 4 are often associated with “swimming pool conjunctivitis.” There are also reports of nosocomial conjunctivitis with adenovirus. Herpes simplex virus can infect the conjunctiva and is among the most common causes of blindness in North America and Europe. 2-13. The answer is d. (Howard, pp 322, 325–328.) Food poisoning with E. coli 0157/H7 causes hemorrhagic colitis; it is often seen after eating beef hamburgers. The same organism also causes a hemorrhagic uremic syndrome. The toxin, called Shiga-like toxin, can be demonstrated in Vero cells,
  • 204 Clinical Vignettes for the USMLE Step 1 but the cytotoxicity must be neutralized with specific antiserum. With the exception of sorbitol fermentation, there is nothing biochemically distinctive about these organisms. 2-14. The answer is e. (Moore & Dalley, pp 300, 347–348.) The obturator nerve runs on the lateral surface of the pelvic wall and exits the pelvis through a canal in the obturator membrane. It innervates the adductor muscles of the medial thigh (a. magnus, a. longus, a. brevis, pectineus, and gracilis). The pudendal nerve exits the pelvic cavity via the greater sciatic foramen and enters the perineum via the lesser sciatic foramen. It innervates the perineal muscles and the skin of the genitalia. The genitofemoral nerve supplies skin over the femoral triangle and scrotum/labia majora. The superior gluteal nerve innervates the gluteus medius and gluteus minimus, which are powerful abductors of the thigh. The femoral nerve innervates the quadriceps muscles, which extend the leg at the knee joint. 2-15. The answer is a. (Baum, pp 116–121.) Having some sense of control over a stressful situation is an important factor in coping with stress and reducing the physiologic reactions to stress. In situations that are uncontrollable, unpredictable, inescapable, or uncertain, the levels of corticosteroids and catecholamines are increased. Furthermore, corticosteroid levels decline more slowly after the termination of an uncontrollable or inescapable stress. Unpredictable shock with no control has also produced an increased incidence of gastric ulceration in animals. In stressful occupational situations, those workers whose jobs are self-paced show fewer symptoms of stress and less catecholamine excretion than those whose jobs are machine-paced. Thus, the potential danger of sustained higher levels of physiologic reactions to stress is reduced by the person’s having some level of control. Situations involving uncertainty also involve an increase in the excretion of epinephrine, norepinephrine, and cortisol. 2-16. The answer is b. (Levinson, pp 306–307.) One of the leading causes of death among AIDS patients is central nervous system toxoplasmosis. It is thought that Toxoplasma infection is a result of reactivation of old or preexisting toxoplasmosis. Occasionally, the infection may be acquired by needle sharing. Because the disease is a reactivation of old or preexisting toxoplasmosis, routine quantitative tests for IgM antibody are usually negative and IgG titers are low (≤1:256, IFA). More sophisticated methods, such as IgM capture or IgG avidity, may reveal an acute response.
  • Block 2 Answers 205 2-17. The answer is a. (Murray, pp 48–73. Scriver, pp 4571–4636. Sack, pp 3–17. Wilson, pp 101–120.) The woman would exhibit respiratory acidosis due to shortness of breath and decreased efficiency of gas exchange in the lungs. Emphysema involves dilated and dysfunctional alveoli from alveolar tissue damage, usually secondary to cigarette smoking. The hypoxia leads to tissue deoxygenation and acidosis, exacerbated by the hypercarbia (CO2 accumulation) that distinguishes respiratory acidosis (higher bicarbonate than expected) from metabolic acidosis (very low bicarbonate, usually with low PCO2 due to compensatory hyperventilation). Choice a shows the only set of values indicating acidosis (pH lower than 7.4), hypoxia (PO2 lower than 95), and hypercarbia (PCO2 greater than 44). The tetrameric structure of hemoglobin allows cooperative binding of oxygen in that binding of oxygen to the heme molecule of the first subunit facilitates binding to the other three. This enhanced binding is due to allosteric changes of the hemoglobin molecule, accounting for its S-shaped oxygen saturation curve as compared with that of myoglobin. At the lower oxygen saturations in peripheral tissues (PO2 30 to 40), hemoglobin releases much more oxygen (up to 50% desaturated) than myoglobin with its single polypeptide structure. The amount of oxygen released (and CO2 absorbed as carboxyhemoglobin) is further increased by the Bohr effect—increasing hydrogen ion (H+) concentration (lowering pH) and increasing CO2 partial pressure (PCO2) shift the sigmoidal-shaped oxygen binding curve for hemoglobin further to the right. 2-18. The answer is c. (Cotran, pp 576–577.) Plaques or vegetations are found in characteristic locations within the heart in several different disorders. Vegetations can occur in acute rheumatic fever as small masses found in a row along the lines of closure of the valves. In contrast, the vegetations of infective endocarditis are large, irregular masses that extend beyond the valves onto the chordae. Nonbacterial thrombotic (marantic) endocarditis, which is associated with prolonged debilitating diseases and cachexia, may produce one or two small, sterile vegetations at the line of valve closure. In patients with systemic lupus erythematosus, medium-sized vegetations (Libman-Sacks endocarditis) may occur on either or both sides of the valve leaflets, typically on the mitral valve and the tricuspid valve. The development of Libman-Sacks endocarditis is associated with the presence of the lupus anticoagulant (antiphospholipid syndrome), an antibody that makes platelets “sticky” and increases the chance of thrombosis.
  • 206 Clinical Vignettes for the USMLE Step 1 2-19. The answer is c. (Hardman, pp 632–633.) Nausea, vomiting, abdominal pain, and diarrhea are early signs of the severe liver toxicity caused by high levels of acetaminophen; other symptoms of acetaminophen toxicity include dizziness, excitement, and disorientation. N-acetyl-L-cysteine is the appropriate treatment for acetaminophen overdose. 2-20. The answer is d. (Murray, pp 123–148. Scriver, pp 2367–2424. Sack, pp 159–175. Wilson, pp 287–317.) All of the poisons shown affect either electron transport or oxidative phosphorylation. Dinitrophenol is unique in that it disconnects the ordinarily tight coupling of electron transport and phosphorylation. In its presence, electron transport continues normally with no oxidative phosphorylation occurring. Instead, heat energy is generated. The same principle is utilized in a well-controlled way by brown fat to generate heat in newborn humans and cold-adapted mammals. The biological uncoupler in brown fat is a protein called thermogenin. Barbiturates, the antibiotic piericidin A, the fish poison rotenone, dimercaprol, and cyanide all act by inhibiting the electron transport chain at some point. 2-21. The answer is b. (McKenzie, p 281. Junqueira, pp 335, 341. Kumar, pp 398–402, Braunwald, p 1455.) The patient suffers from emphysema, in which neutrophils enter the lung parenchyma and secrete elevated levels of elastase, leading to the destruction of the bronchiolar and alveolar septal elastic tissue support. The destruction of the elasticity in emphysema leads to diminished breath sounds. This is coupled with faint high-pitched rhonchi at the end of expiration and a hyperresonant percussion note. The rhonchi are adventitious (not normally present) sounds that may be high pitched, generally because of bronchospasm, or low pitched, generally because of the presence of airway secretions. Emphysema is a disease characterized by parenchymal tissue destruction and, therefore, is not associated with adventitious breath sounds. However, because most emphysema is due to cigarette smoking, there is almost always some degree of chronic bronchitis, and therefore, rhonchi can be auscultated. There are genetic and environmental causes of emphysema. The environmental causes include smoking and air pollution, whereas deficiency in α1-antitrypsin (antiprotease) activity is the genetic cause of the disease. The balance between normal elastase-elastin production and proteaseantiprotease activity is altered in emphysema. Persons with a deficiency in
  • Block 2 Answers 207 α1-antitrypsin activity lack sufficient antiprotease activity to counteract neutrophil-derived elastase. When there is an increase in the entry and activation of neutrophils in the alveolar space, more elastase is released, and elastic structures are destroyed. In smoking there is an increase in the number of neutrophils and macrophages in alveoli and increased elastase activity from neutrophils and macrophages. These changes are coupled with a decrease in antielastase activity because of oxidants in cigarette smoke and antioxidants released from the increased numbers of neutrophils. The increased protease activity causes breakdown of the alveolar walls and dissolution of elastin in the bronchiolar walls. The loss of tethering of the bronchioles to the lung parenchyma leads to their collapse. The bronchioles, unlike the trachea and bronchi, do not contain hyaline cartilage. A relatively thick layer of smooth muscle is found in the bronchioles, but the bronchioles are tethered to the lung parenchyma by elastic tissue, which plays a key role in the stretch and recoil of the lungs during inhalation and exhalation. 2-22. The answer is a. (Plomin, pp 188–192.) Twin studies have consistently shown a strong genetic effect for the heritability of attention deficit hyperactivity disorder (ADHD). The findings show the heritability to be about 70%. The genetic component for ADHD is stronger than for most other psychopathologies except autism. Adoption studies also support the high heritability of ADHD. The Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) defines ADHD as a disorder in which a child is very restless, has a poor attention span, and acts impulsively. Prevalence is about 4% of elementary school children, with boys outnumbering girls. European psychiatrists put more emphasis on the pervasive hyperactivity and early onset, but not on high anxiety. One problem with the DSM-IV grouping ADHD with disruptive behavior disorder is that disruptive behavior disorder shows only modest genetic influence and doesn’t involve hyperactivity or inattentiveness. Nevertheless, there is some overlap between hyperactivity and conduct disorder symptoms, e.g., early onset hyperactivity has an increased risk for the later onset of conduct problems. However, the comorbidity rate has diminished for the “pure” ADHD probands who do not show symptoms of conduct disorder. 2-23. The answer is d. (Cotran, pp 148, 1254–1255. Champe, 348–349.) Purine synthesis involves adding carbons and nitrogens to ribose
  • 208 Clinical Vignettes for the USMLE Step 1 5-phosphate (R5P), which is a product of the hexose monophosphate (HMP) shunt. R5P is then converted to ribose phosphate pyrophosphate (RPPP), which is subsequently converted to 5′-phosphoribosylamine, the latter step being the committed step in purine nucleotide biosynthesis. Through a series of steps RPPP is converted to inosine 5′-monophosphate (IMP). Several of these biochemical steps involve transferring methyl groups from folate. This is important because folate analogues, such as methotrexate, inhibit DNA synthesis, especially in rapidly growing tumor cells, by inhibiting purine synthesis. Finally IMP is converted into either AMP or GMP. These last biochemical steps are also connected to biochemical reactions that involve adenosine deaminase, an enzyme that is deficient in individuals with the autosomal recessive form of SCID, and hypoxanthine-guanine phosphoribosyl transferase (HGPRT), an enzyme of the purine salvage pathway for recycling guanine and hypoxanthine that is deficient in individuals with the X-linked recessive disorder LeschNyhan syndrome. This disorder is characterized by excess uric acid production, which may produce symptoms of gout, mental retardation, spasticity, self-mutilation, and aggressive behavior. In contrast, a deficiency of homogentisic oxidase, which is involved in the conversion of homogentisic acid to methylacetoacetate, is associated with alkaptonuria. Abnormal degradation of galactocerebroside is seen in Krabbe’s disease, while abnormal breakdown of branched-chain amino acids is seen in maple syrup urine disease. 2-24. The answer is c. (Murray, pp 123–148. Scriver, pp 2367–2424. Sack, pp 159–175. Wilson, pp 287–317.) The most likely cause of the symptoms observed is carnitine deficiency. Under normal circumstances, long-chain fatty acids coming into muscle cells are activated as acyl coenzyme A and transported as acyl carnitine across the inner mitochondrial membrane into the matrix. A deficiency in carnitine, which is normally synthesized in the liver, can be genetic; but it is also observed in preterm babies with liver problems and dialysis patients. Blockage of the transport of long-chain fatty acids into mitochondria not only deprives the patient of energy production, but also disrupts the structure of the muscle cell with the accumulation of lipid droplets. Oral dietary supplementation usually can effect a cure. Deficiencies in the carnitine acyltransferase enzymes I and II can cause similar symptoms.
  • Block 2 Answers 209 2-25. The answer is e. (Murray, pp 1406–1412.) Cyclosporiasis is a newly recognized food- and water-borne infectious disease associated with eating contaminated berries imported from some Central American countries. Cyclospora are moderately acid-fast but twice the size of Cryptosporidium. Patients usually have frequent diarrhea for up to 3 weeks and usually suffer only malaise and fatigue. The disease is self-limiting, but relapses can occur. 2-26. The answer is g. (Katzung, pp 170–171.) Sodium nitroprusside reduces blood pressure by dilating both arterial and venous vessels. It most likely acts by releasing nitric oxide, which reacts with guanylyl cyclase. This results in an increase in intracellular cyclic guanosine 5′-monophosphate [cyclic GMP (cGMP)], a vascular smooth-muscle relaxant. Another possible explanation for increased intracellular levels of GMP is the direct action of sodium nitroprusside on guanylyl cyclase. Sodium nitroprusside is a useful agent in the treatment of hypertensive emergencies because of its rapid onset and short duration of action. 2-27. The answer is a. (Cotran, p 1210.) Fungal infections of the skin can be classified into superficial mycoses, cutaneous mycoses, and subcutaneous mycoses. The superficial mycoses are characterized by infection of the superficial layers of the skin. The most common type is pityriasis versicolor (tinea versicolor), an infection of the upper trunk that is caused by M. furfur (Pityrosporum orbiculare). Clinically, there are multiple groups of macules (discolorations) with a fine peripheral scale. These macules are hyperpigmented (dark) in white-skinned races but hypopigmented (light) in dark-skinned races. These areas fluoresce yellow under a Wood’s lamp. Potassium hydroxide (KOH) is used to identify fungal infections from scrapings of the skin. The KOH dissolves the keratin, and then the mycelial fungi can be seen. With tinea versicolor, KOH examination reveals a characteristic “spaghetti and meatball” appearance. The fragments of hyphae are the “spaghetti,” while the round yeast cells are the “meatballs.” Different types of tinea include tinea capitis, tinea corporis, tinea pedis (athlete’s foot), and tinea versicolor. 2-28. The answer is e. (Murray, pp 307–346. Scriver, pp 1667–1724. Sack, pp 121–138. Wilson, pp 287–317.) Collagen has an unusual amino acid composition in that approximately one-third of collagen molecules are
  • 210 Clinical Vignettes for the USMLE Step 1 glycine. The amino acid proline is also present in a much greater amount than in other proteins. In addition, two somewhat unusual amino acids, 4-hydroxyproline and 5-hydroxylysine, are found in collagen. Hydroxyproline and hydroxylysine per se are not incorporated during the synthesis of collagen. Proline and lysine are hydroxylated by specific hydroxylases after collagen is synthesized. A reducing agent such as ascorbate (vitamin C) is needed for the hydroxylation reaction to occur. In its absence, the disease known as scurvy occurs. Only proline or lysine residues located on the amino side of glycine residues are hydroxylated. The hydroxylysine residues of collagen are important sites of glycosylation of disaccharides of glucose and galactose. 2-29. The answer is a. (April, pp 133, 140.) The deep incisure in the inferior border of the pedicle ensures that the spinal nerve associated with that vertebra will exit through the intervertebral foramen well above the intervertebral disk so that it will not be affected by a herniation at that level. However, a posterolateral herniation (the usual direction) will impinge on the next lower nerve as it courses toward its associated intervertebral foramen. In this case, pain was distributed along the medial side of the leg and foot as far as the great toe—the distribution of the saphenous branch of the femoral nerve (L4). Herniation of the third lumbar intervertebral disk between vertebral bodies L3–L4 would affect nerve L4. 2-30. The answer is c. (Hardman, p 546.) Pentazocine is a mixed agonistantagonist of opioid receptors. When a partial agonist, such as pentazocine, displaces a full agonist, such as methadone, the receptor is less activated; this leads to withdrawal syndrome in an opioid-dependent person. 2-31. The answer is c. (Cotran, p 1079–1080.) Ectopic pregnancy is a potentially life-threatening condition if it is not treated by removal before rupture and hemorrhage with fatal exsanguination. The most common location for extrauterine implantation is the fallopian tube (more than 85% of cases), with rare implantation in the ovary or abdomen. If the tubal implantation has existed for 1 to 4 weeks, the β-hCG test result is likely to be negative; thus a negative result does not exclude pregnancy. It is always worthwhile to repeat a laboratory test when the result is unexpected. Tubal pregnancy is not uncommon and should always be considered if endometrial samples suggest gestational change without chorionic villi.
  • Block 2 Answers 211 2-32. The answer is b. (Plomin, pp 26–37.) Complex behavioral traits such as schizophrenia, which may vary widely in nature from person to person, are considered to involve anomalies at more than one gene locus. The science of behavior genetics deals with the quantitative analysis of these polygenic traits. The results of a great variety of investigations now favor the view that schizophrenia is a genetically determined disorder, but it also may be substantially affected by environmental influences. 2-33. The answer is c. (Moore & Dalley, p 345.) The puborectalis, pubococcygeus, and iliococcygeus comprise the levator ani, the main muscular component of the pelvic floor. The pubococcygeus is the part of the levator ani most frequently damaged during parturition. Because the pubococcygeus surrounds and supports the neck of the bladder and the proximal urethra, urinary leakage is a common result, particularly during increased abdominopelvic pressure, e.g., during coughing. Damage to the puborectalis would result in fecal incontinence under similar situations. Both the obturator internus muscle and the piriformis are parts of the lateral wall of the pelvis and assist in lateral rotation of the thigh. 2-34. The answer is a. (Braunwald, pp 618–619.) Hypercalcemia of malignancy is the most common paraneoplastic syndrome. It accounts for about 40% of all hypercalcemia. The signs and symptoms of hypercalcemia include bone pain, irritability, weakness, fatigue, constipation, nausea, and vomiting, as this patient manifests. Symptoms begin at a serum calcium of about 2.6 mmol/L. Hypercalcemia of malignancy is common in cancers with squamous cell histology. 2-35. The answer is c. (Murray, pp 48–62. Scriver, pp 3–45. Sack, pp 1–3. Wilson, pp 101–120.) Protein electrophoresis is an important laboratory technique for investigating red cell proteins such as hemoglobin or plasma proteins such as the immunoglobulins. The proteins are dissolved in a buffer of low pH where the amino groups of amino acid side chains are positively charged, causing most proteins to migrate toward the negative electrode (anode). Red cell hemolysates are used for hemoglobin electrophoresis, plasma (blood supernatant with unhemolyzed red cells removed) for plasma proteins. Serum (blood supernatant after clotting) would not contain red cells but would contain many blood enzymes and proteins. In sickle cell anemia, the hemoglobin S contains a valine substitution for the
  • 212 Clinical Vignettes for the USMLE Step 1 glutamic acid at position 6 in hemoglobin A. Hemoglobin S thus loses two negative charges (loss of a glutamic acid carboxyl group on each of two β-globin chains) compared to hemoglobin A. Hemoglobin S is thus more positively charged and migrates more rapidly toward the anode than hemoglobin A. Lane B must represent the heterozygote with sickle cell trait (hemoglobins S and A), establishing lane A as the normal and lane D as the sickle cell anemia sample. The hemoglobin in lane C migrates differently from normal and hemoglobin S, as would befit an abnormal hemoglobin that is different from S. 2-36. The answer is d. (Katzung, pp 779–780.) Erythromycin is safe to use in pregnancy and is effective against Chlamydia. Levofloxacin is contraindicated in pregnancy because animal studies have identified that cartilage erosion can occur during growth. Chlamydia are not sensitive to gentamycin, however, it probably should not be used in pregnancy because of potential nephro- and ototoxicity. Tetracycline may cause tooth enamel dysplasia and problems with bone during fetal development. Sulfamethoxazole-trimethoprim has severe consequences, particularly in the newborn, because it displaces bilirubin from albumin, which is then deposited in the brain causing a condition referred to as kernicterus. 2-37. The answer is c. (Gutyon, pp 360–363.) Increasing bicarbonate concentration in the plasma results in a metabolic alkalosis. To compensate for the alkalosis, the respiratory system decreases alveolar ventilation. Therefore, an increase in plasma bicarbonate and arteriolar PCO2 is characteristic of metabolic alkalosis. The respiratory system will not allow arteriolar PCO2 to increase much above 50 mmHg, so respiratory compensation for a metabolic alkalosis is limited. A similar limitation is not present when metabolic acidosis occurs, so respiratory compensation can reduce arteriolar PCO2 to below 10 mmHg. Although NaHCO3− ingestion does not typically cause metabolic alkalosis, its use is not recommended because alkalosis may occur and because it may result in Na+ retention. 2-38. The answer is e. (Cotran, pp 1039–1040, 1065.) Pelvic inflammatory disease (PID) is a common disorder caused by infection with either gonococci (the most common cause), chlamydiae, or enteric bacteria. Gonococcal infection, seen microscopically as gram-negative intracellular
  • Block 2 Answers 213 diplococci, begins in the Bartholin’s glands and then spreads upward to involve the fallopian tubes and tuboovarian regions. This produces PID, which is characterized by pelvic pain, fever, adnexal tenderness, and pain when the cervix is manipulated. Complications of PID include peritonitis from rupture of a tuboovarian abscess, infertility, and intestinal obstruction. 2-39. The answer is d. (Murray, pp 48–62. Scriver, pp 3–45. Sack, pp 1–3. Wilson, pp 101–120.) Collagen peptides assemble into helical tertiary structures that form quaternary triple helices. The triple helices in turn assemble end to end to form collagen fibrils that are essential for connective tissue strength. Over 15 types of collagen contribute to the connective tissue of various organs, including the contribution of type I collagen to eyes, bones, and skin. The fact that only one of two α2 alleles is normal in this case implies that a mutant α2 allele could be responsible for the disease (even if the α2 locus is on the X chromosome, since the baby is female with two X chromosomes). The mutant α2 collagen peptide would be incorporated into half of the type I collagen triple helices, causing a 50% reduction in normal type I collagen. (A mutant α1 collagen peptide would distort 75% of the molecules since two α1 peptides go into each triple helix). The ability of one abnormal collagen peptide allele to alter triple helix structure with subsequent degradation is well documented and colorfully named protein suicide or, more properly, a dominant-negative mutation. 2-40. The answer is a. (Levinson, pp 212–213, 218–219, 219–220, 214– 215.) Varicella-zoster virus is a herpesvirus. Chickenpox is a highly contagious disease of childhood that occurs in the late winter and early spring. It is characterized by a generalized vesicular eruption with relatively insignificant systemic manifestations. Adenovirus has been associated with adult respiratory disease among newly enlisted military troops. Crowded conditions and strenuous exercise may account for the severe infections seen in this otherwise healthy group. Papillomavirus is one of two members of the family Papovaviridae, which includes viruses that produce human warts. These viruses are hostspecific and produce benign epithelial tumors that vary in location and clinical appearance. The warts usually occur in children and young adults and are limited to the skin and mucous membranes.
  • 214 Clinical Vignettes for the USMLE Step 1 Rotavirus is worldwide in distribution and has been implicated as the major etiologic agent of infantile gastroenteritis. Infection with this virus varies in its clinical presentation from asymptomatic infection to a relatively mild diarrhea to a severe and sometimes fatal dehydration. The exact mode of transmission of this infectious agent is not known. Because of severe side effects, the rotavirus vaccine has been recalled and is temporarily unavailable. Infectious mononucleosis caused by cytomegalovirus (CMV) is clinically difficult to distinguish from that caused by Epstein-Barr virus. Lymphocytosis is usually present with an abundance of atypical lymphocytes. CMV-induced mononucleosis should be considered in any case of mononucleosis that is heterophil-negative and in patients with fever of unknown origin. 2-41. The answer is c. (Braunwald, pp 348, 656, 658, 1574, 1590. McKenzie, p 223. Junqueira, pp 234–237.) The most likely cause of the anemia is renal failure, leading to decreased production of the kidney– derived red blood cell growth factor, erythropoietin. In the initial stages of renal failure the kidneys will increase their production of erythropoietin, but as renal damage continues the cells that produce this factor are destroyed. Therefore, there are initially increased levels of reticulocytes (immature red blood cells) in the bloodstream, but as in the anemia of renal disease, low production of reticulocytes is a hallmark of the disease. Although the patient may have decreased estrogen levels, estrogen decreases hematocrit. Also, women who are pregnant (third trimester) can have slightly decreased hematocrits [37 Ϯ 6 (third trimester pregnant women) vs. 40 Ϯ 6 (adult women) and 42 Ϯ 6 (postmenopausal women)]. Administration of recombinant erythropoietin (EPO) is the preferred treatment for anemia caused by advanced renal disease. Generally, EPO is administered if the hematocrit is less than 30% and whether the patient is on dialysis. Erythropoietin is synthesized by the peritubular (interstitial) cells of the kidney cortex, stimulates the differentiation of cells from the erythrocyte colony–forming units (E-CFUs) and stimulates the differentiation and release of reticulocytes from the bone marrow. Colony-forming units (CFUs) are distinct cell lineages derived from pluripotential stem cells in the bone marrow.
  • Block 2 Answers 215 2-42. The answer is a. (Hardman, pp 1660–1661.) Arsenic is an active constituent of fungicides, herbicides, and pesticides. Symptoms of acute toxicity include tightness in the throat, difficulty in swallowing, and stomach pains. Projectile vomiting and severe diarrhea can lead to hypovolemic shock and death. Chronic poisoning may cause peripheral neuritis, anemia, skin keratosis, and capillary dilation leading to hypotension. Dimercaprol is the primary agent used in the treatment of arsenic poisoning. 2-43. The answer is a. (Raoult, pp 284–285.) Dengue (breakbone fever) is caused by a group B togavirus that is transmitted by mosquitoes. The clinical syndrome usually consists of a mild systemic disease characterized by severe joint and muscle pain, headache, fever, lymphadenopathy, and a maculopapular rash. Hemorrhagic dengue, a more severe syndrome, may be prominent during some epidemics; shock and occasionally death result. 2-44. The answer is d. (Hardman, p 906.) Cimetidine slows the metabolism of Ca channel blockers, which are substrates for hepatic mixed-function oxidases. Inhibition of cytochrome P450 activity is peculiar to cimetidine and is not a mechanism of action of other histamine 2 (H2) blockers. 2-45. The answer is a. (Kandel, pp 36–60.) Humans have a number of simple behaviors that resemble the fixed action patterns of lower animals. Such emotional expressions as the startle response and smiling are stereotyped sequences of movements. In human infants smiling appears to be under the control of a specific sign stimulus. Studies show that the smiling response is not triggered by the face as a whole, but rather by certain specific features. For example, the eyes are of particular importance as a sign stimulus, and as the child matures, other features of the face become important. The brow flash response (rapid raising and dropping of eyebrows) is a stereotyped response present in widely different cultures and is used as part of a greeting response. A complex set of human behaviors that is universal in emotional expression across cultures and that involves a stereotyped sequence of fixed action patterns includes the facial expressions of anger, fear, disgust, and joy. As an example, babies who are born blind can have emotional facial expressions that appear normal. While apprehension may include some of the responses also found in fear, it does not include as many, nor are the responses as severe.
  • 216 Clinical Vignettes for the USMLE Step 1 2-46. The answer is b. (Cotran, pp 564–566. Abenhaim, pp 609–616. Connolly, pp 581–588.) Hypertensive heart disease (HHD) can be divided into systemic HHD and pulmonary HHD. Systemic HHD is the result of systemic hypertension, which causes left ventricular (LV) hypertrophy. There is by definition no other cardiac disease present that could cause LV hypertrophy, such as aortic stenosis. Hypertension is a pressure overload on the heart, and as such it causes concentric LV hypertrophy without dilation. In contrast, eccentric hypertrophy is the result of volume overload on the heart. In systemic HHD the LV is stiff, as there is decreased LV compliance. In a patient with uncontrolled hypertension, LV dilation would indicate LV failure. Pulmonary HHD indicates right ventricular hypertrophy that is the result of pulmonary disease. By definition, this type of heart disease is called cor pulmonale. Pulmonary diseases that can cause cor pulmonale include diseases of the lung parenchyma, such as chronic obstructive pulmonary disease and interstitial fibrosis, and diseases of the pulmonary vessels, such as multiple pulmonary emboli and pulmonary vascular sclerosis. The latter has been associated with the use of the combination of diet drugs fenfluramine and phentermine. (This combination has been referred to as Fen-Phen.) 2-47. The answer is e. (Braunwald, p 1986.) The suppression of ACTH is characteristic of adrenal adenoma or carcinoma. A CT scan will evaluate for the presence of adrenal tumor. Chest CT is useful in ectopic ACTH secretion. A MRI of the pituitary is useful in pituitary dependent Cushing’s disease. The ACTH stimulation test and serum ADH are not diagnostic in this disease. 2-48 and 2-49. The answers are 2-48 c, 2-49 c. (Afifi, pp 133–134.) The central pathways mediating taste include the following: primary afferent taste fibers associated with taste receptors of cranial nerves VII, IX, and X synapse in the solitary nucleus. Many fibers from the solitary nucleus project to the ventral posteromedial nucleus of the thalamus, which, in turn, project to the ventrolateral aspect of the postcentral gyrus. 2-50. The answer is b. (Kumar, pp 249, 251. Greenspan, pp 320–322. Junqueira, pp 145–148. Braunwald, pp 2201–2204.) The patient suffers from osteomalacia, a disease related to malnutrition, specifically vitamin D defi-
  • Block 2 Answers 217 ciency. On the basis of the first bone biopsy in which the tissue was decalcified, one could make a diagnosis of osteoporosis. The second, nondecalcified bone biopsy indicates that osteoid is being formed but is not undergoing mineralization. This correlates with the low 25-hydroxyvitamin D levels. Vitamin D replacement and calcium supplementation would be prescribed for this patient.
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  • BLOCK 3 Answers 3-1. The answer is d. (Braunwald, pp 628–629.) Any back pain in a patient with a known history of carcinoma should be evaluated for the possibility of spinal cord compression. It occurs in 5 to 10% of patients with cancer. Lung cancer is the most common primary malignancy causing spinal cord compression. Localized back pain and tenderness are the most common initial complaints. 3-2. The answer is b. (Braunwald, pp 2041–2042. Moore, Before We are Born, pp 155, 157. Moore, Developing Human, pp 121–122, 171, 172, 174–175.) Cells from a patient with the most common form of Klinefelter syndrome (47,XXY genotype) will have one inactive X chromosome and, therefore, one Barr body. The formula is the number of Barr bodies equals the number of X chromosomes minus one. Klinefelter syndrome occurs about 1:500 males and is due to meiotic nondisjunction of the chromosomes. The nondisjunction is more frequent in oogenesis than spermatogenesis, and increased occurrence is directly proportional to increasing maternal age. Klinefelter may occur as 47,XXY, 48,XXYY, 48,XXXY, and 49,XXXXY. A combination of abnormal and normal genotype occurs in mosaic individuals who generally have less severe symptoms. Females have two X chromosomes, one of maternal and the other of paternal origin. Only one of the X chromosomes is active in the somatic, diploid cells of the female; the other X chromosome remains inactive and is visible in appropriately stained interphase cells as a mass of heterochromatin. Detection of the Barr body (sex chromatin) has been an efficient method for the determination of chromosomal sex and abnormalities of X-chromosome number; however, it is not definitive proof of maleness or femaleness. The genotypic sex of Klinefelter syndrome and XXX individuals would be male and female as determined by the presence or absence of the testis-determining Y chromosome. In Turner’s syndrome (XO), no Barr bodies would be present. In comparison, “superfemales” (XXX) would possess two inactive X chromosomes (2 219 Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  • 220 Clinical Vignettes for the USMLE Step 1 Barr bodies) and one active X chromosome. Buccal scrapings for Barr body analysis are being used less—chromosomal analysis is becoming the standard test now. 3-3. The answer is d. (Hardman, pp 1247, 1335.) Leucovorin prevents methotrexate from inhibiting dihydrofolate reductase and reverses all of its adverse effects except neurotoxicity. 3-4. The answer is b. (Afifi, pp 82–85.) The medial vestibulospinal tract arises from the medial vestibular nucleus and descends in the medial longitudinal fasciculus to cervical levels where it controls LMNs, which innervate (flexor) muscles controlling the position of the head. The lateral vestibulospinal tract facilitates extensor motor neurons of the limbs; the rubrospinal tract facilitates flexor motor neurons of the limbs; and the reticulospinal tracts modulate muscle tone of the limbs. 3-5. The answer is a. (Hardman, pp 977–978.) Primaquine is effective against the extraerythrocytic forms of P vivax and P ovale and is thus of . . value in a radical cure of malarial infection. It also attacks the sexual forms of the parasite, rendering them incapable of maturation in the mosquito and making it valuable in preventing the spread of malarial infection. 3-6. The answer is c. (Cotran, pp 649–650. Chandrasoma, pp 433–443.) Lymph nodes may be enlarged (lymphadenopathy) secondary to reactive processes, which can be either acute or chronic. Acute reaction (acute nonspecific lymphadenitis) can result in focal or generalized lymphadenopathy. Focal lymph node enlargement is usually the result of bacterial infection. Sections from involved lymph nodes reveal infiltration by neutrophils. In contrast, generalized acute lymphadenopathy is usually the result of viral infections and usually produces a proliferation of reactive T lymphocytes called T immunoblasts. These reactive T cells tend to have prominent nucleoli and can be easily mistaken for malignant lymphocytes or malignant Hodgkin cells. Reactive processes involving lymph nodes typically involve different and specific portions of the lymph nodes depending upon the type of cell that is reacting. For example, reactive B lymphocytes typically result in hyperplasia of the lymphoid follicles and germinal centers (follicular hyperplasia). Examples of diseases that are associated with follicular hyper-
  • Block 3 Answers 221 plasia include chronic inflammation caused by organisms, rheumatoid arthritis, and AIDS. Lymph nodes from patients with AIDS undergo characteristic changes that begin with follicular hyperplasia with loss of mantle zones, intrafollicular hemorrhage (“follicle lysis”), and monocytoid B cell proliferation. Subsequently there is depletion of lymphocytes (CD4+ lymphocytes) in both the follicles and the interfollicular areas. In contrast to reactive B cell processes, reactive T lymphocytes typically result in hyperplasia involving the T cell areas of the lymph node, namely the interfollicular regions and the paracortex. Examples of clinical situations associated with a T lymphocyte response include viral infections, vaccinations, use of some drugs (particularly Dilantin), and systemic lupus erythematosus. The sinusoidal pattern of reaction involves expansion of the sinuses by benign macrophages, as seen in reactive proliferations of the mononuclearphagocytic system. Stellate microabscesses (irregular areas composed of central necrotic cellular and neutrophil debris surrounded by palisading macrophages) are characteristic of cat-scratch disease, lymphogranuloma venereum, and tularemia. 3-7. The answer is b. (Ryan, p 505.) Herpes simplex virus causes primary and recurrent disease. The typical skin lesion is a vesicle that contains virus particles in serous fluid. Giant multinucleated cells are typically found at the base of the herpesvirus lesion. Encephalitis, which usually involves the temporal lobe, has a high mortality rate. Severe neurologic sequelae are seen in surviving patients. 3-8. The answer is a. (Coe, pp 1042–1052. Kumar, pp 673–675. Greenspan, pp 326–329.) The correct diagnosis is Paget’s disease, also known as osteitis deformans because of its deforming capabilities (e.g., skull or femoral head enlargement). In this disease the serum calcium is normal, but there is an increase in osteoclastic activity (osteolytic lesions and elevated 24-h urine hydroxyproline) and an increase in osteoblastic activity (elevated osteocalcin and alkaline phosphatase). Patients with Paget’s disease exhibit a marked increase in osteoid, and the bone actually enlarges. The osteoid is never normally mineralized in this disease. In this patient, the bone scan shows significant uptake of labeled bisphosphonates, which are incorporated into newly formed osteoid during bone formation. Her proximal femur is enlarged and no longer fits properly into the acetabulum, which results in the hip pain.
  • 222 Clinical Vignettes for the USMLE Step 1 There are a number of useful biochemical markers of bone metabolism. Osteoclasts synthesize tartrate–resistant acid phosphatase so that increased osteoclastic activity is reflected in increased serum levels of tartrate–resistant acid phosphatase. Bone resorption fragments of type I collagen and noncollagenous proteins increase as bone matrix is resorbed. Hydroxyproline is a good urinary marker of bone metabolism because hydroxyproline is released and excreted in the urine as collagen is broken down. The presence of pyridinoline cross-links, which are involved in the bundling of type I collagen, is used for measurement of bone resorption. These cross-links are released only during degradation of mineralized collagen fibrils as occurs in bone resorption. Usually, pyridinoline cross-links are measured by immunoassay over a 24-h period to detect excess bone resorption and collagen breakdown in disorders such as Paget’s disease. Markers of bone formation include osteocalcin, alkaline phosphatase, and the extension peptides of type I collagen. Osteocalcin is a vitamin K–dependent gla (γ-carboxyglutamic acid) protein that is synthesized by osteoblasts and secreted into the serum in an unchanged state. Serum concentrations of osteocalcin are, therefore, directly related to osteoblastic activity. It is a more specific marker than the marker alkaline phosphatase, because other organs, such as the liver and kidney, produce that enzyme. Radiologic methods such as conventional x-ray can be used to detect osteoporosis, but only after patients have lost 30 to 50% of their bone mass. Dual-beam photon absorptiometry allows a much more accurate diagnosis of loss of bone mass. 3-9. The answer is b. (Moore & Dalley, pp 256–257.) Infectious mononucleosis is a virus-induced illness leading to swollen lymph nodes and spleen. The splenomegaly is evidenced by the very rounded contours of the organ. Infectious mononucleosis can exhibit liver involvement; however, the organ indicated is not the liver but the spleen in the upper left hypochondrium. The bright organ between it and the vertebra is the left kidney. The liver is on the opposite side of the abdominal cavity. 3-10. The answer is a. (Guyton, pp 948–949.) Continuous secretion of progesterone by the corpus luteum is essential for development of the fetus. During the first trimester, placental production of hCG sustains the corpus luteum and ensures continued progesterone secretion. By the second trimester, progesterone production by the placenta increases to levels sufficient to sustain fetal growth and development.
  • Block 3 Answers 223 3-11. The answer is d. (Cotran, pp 1221–1222.) Osteogenesis imperfecta (OI), or brittle bone disease, constitutes a group of disorders often inherited as autosomal dominant traits and caused by genetic mutations involving the synthesis of type I collagen, which comprises about 90% of the osteoid, or bone matrix. Very early perinatal death and multiple fractures occur in OI type II, which is often autosomal recessive. The major variant of OI, type I, is compatible with survival; after the perinatal period fractures occur in addition to other signs of defective collagen synthesis such as thin, translucent, blue scleras; laxity of joint ligaments; deafness from otosclerosis; and abnormal teeth. A hereditary defect in osteoclastic function with decreased bone resorption and bone overgrowth, which sometimes narrows or obliterates the marrow cavity, is characteristic of osteopetrosis, or marble bone disease. Osteomalacia is seen in adults due to vitamin D deficiency, while osteitis deformans is Paget’s disease of bone. 3-12. The answer is a. (Raoult, p 356.) With an acute case of primary infection by Epstein-Barr virus (EBV), such as infectious mononucleosis, IgM antibodies to VCA should be present. Antibodies to EBNA should be absent, as they usually appear 2 to 3 months after onset of illness. Culture is not clinically useful because it (1) requires freshly fractionated cord blood lymphocytes, (2) takes 3 to 4 weeks for completion, and (3) is reactive in the majority of seropositive patients. 3-13. The answer is e. (Hardman, p 745.) Vasodilator therapy for CHF has gained prominence in the past 10 years. The ACE inhibitors, such as enalapril, are among the best agents for this purpose, although Ca channel inhibitors and nitroglycerin can also be used. The ACE inhibitors dilate arterioles and veins (reducing preload), as well as inhibit aldosterone production (reducing blood volume), factors considered beneficial in CHF therapy. Both β-adrenergic antagonists and ACE inhibitors have been shown to increase survival in CHF . 3-14. The answer is a. (McPhee, p 148; Braunwald, pp 134–142.) Although various areas of the cerebral cortex are specialized to perform certain functions, the cognitive and behavioral domains (language, memory, calculation ability, and so forth) are interconnected to both cortical and subcortical neural networks. Specific deficits identified in a careful neurologic exam will help define which area or network has been damaged. Aphasia is an abnormality of language. Anomia, the inability to name, is a
  • 224 Clinical Vignettes for the USMLE Step 1 form of aphasia. Apraxia is a complex motor deficit not attributable to pyramidal, extrapyramidal, cerebellar, or sensory abnormalities. 3-15. The answer is d. (Baum, pp 304–306.) There is an increased interest in self-control or self-management programs in terms of what individuals can do for themselves. Many weight loss programs have established that selfreward is the most effective tool during both posttreatment and follow-up. Self-reward acts as a contingent reinforcement for losing weight. Selfmonitoring is a part of some self-management programs, but is not as effective as self-reward. Self-control procedures have been applied to other areas, such as self-management of diabetes where patients can pay attention to specific adaptive behaviors that they can control. Thus, self-reinforcement becomes a powerful cognitive-behavioral intervention. 3-16. The answer is b. (Moore & Dalley, pp 775, 821–822.) The patient has a classic case of carpal tunnel syndrome, in which the median nerve is compressed as it passes through the carpal tunnel formed by the flexor retinaculum in the wrist. Evidence for involvement of the median nerve is weakness and atrophy of the thenar muscles (abductor pollicis brevis, opponens pollicis) and lumbricals 1 to 3. Sensory deficits also follow the distribution of the median nerve. The median nerve enters the hand, along with the tendons of the superficial and deep digital flexors, through a tunnel framed by the carpal bones and the overlying flexor retinaculum. Symptoms are worse in the early morning and in pregnancy because of fluid retention, resulting in swelling that entraps the median nerve. Flexing the wrist for an extended period exaggerates the paresthesia (“Phelan’s” sign) by increasing pressure on the median nerve. Neither the ulnar nerve, radial nerve, nor radial artery passes through the carpal tunnel. The ulnar nerve supplies the third and fourth lumbricals and only the short adductor of the thumb. The radial nerve innervates mostly long and short extensors of the digits and the dorsal aspect of the hand. Proper digital nerves lie distal to the carpal tunnel but are only sensory. 3-17. The answer is e. (Hardman, p 72.) Activated charcoal, a fine, black powder with a high adsorptive capacity, is considered to be a highly valuable agent in the treatment of many kinds of drug poisoning. Drugs that are well adsorbed by activated charcoal include primaquine, propoxyphene, dextroamphetamine, chlorpheniramine, phenobarbital, carbamazepine, digoxin,
  • Block 3 Answers 225 and aspirin. Mineral acids, alkalines, tolbutamide, and other drugs that are insoluble in acidic aqueous solution are not well adsorbed. Charcoal also does not bind Ca, lithium (Li), or Fe. 3-18. The answer is d. (Braunwald, pp 1051–1052.) Infection with Coxiella burnetii (or Q fever) represents an occupational hazard of veterinarians. Q fever is characterized by fever, extreme fatigue, and headache, and about one-fourth of persons with the infection develop thrombocytopenia, unlike in the other infections. Mycoplasma pneumoniae infection is insidious and causes pneumonia as does Chlamydia pneumoniae infection; thrombocytopenia is not a characteristic of these infections. Influenza develops rapidly, in 2 to 3 days from exposure. 3-19. The answer is d. (Sierles, pp 9–11. Wedding, pp 366–377.) A depressed mood and depressive illnesses are the most common psychosocial reactions of persons with AIDS. A depressive illness can be secondary to a viral infection of the brain and nervous system or a side effect of drugs used to treat AIDS, or it can arise from preexisting mood disorders. Depressed mood and depressive illnesses can also occur from psychosocial stress generated from such factors as reception of a fatal diagnosis, loss of confidentiality, stigma of having AIDS, rejection by friends and family, loss of independence, loss of bowel and bladder control, or loss of occupational competence. Adaptation is a psychosocial factor that affects depression, especially in terms of what the illness means to the patient—e.g., the illness as a challenge, an enemy, a punishment, a weakness, a strategy for life, an irreparable loss or injury, an incentive to change behavior, or a threat to coping capacities. Some of the behaviors that can be observed in depressed moods and illnesses include a sad, apathetic, or anxious mood, loss of selfesteem, guilt, hopeless or helpless feelings, insomnia, loss of appetite, and suicidal thoughts. 3-20. The answer is c. (Martin, pp 42–49; Afifi, pp 148–153.) The combined deficit in which the patient loses ability to (use his lateral rectus muscle) abduct his right eye and display facial expression on the right side of the face means that the lesion is located in the dorsal pons at the site where the facial nerve curves around (just above) the motor nucleus of cranial nerve VI. Thus, a lesion at this site will affect both cranial nerves, causing the combined deficits described previously.
  • 226 Clinical Vignettes for the USMLE Step 1 3-21. The answer is a. (Cotran, pp 177–179.) Fragile X syndrome is one of four diseases that are characterized by long repeating sequences of three nucleotides. The other diseases are Huntington’s disease, myotonic dystrophy, and spinal and bulbar muscular atrophy. The fragile X syndrome, which is more common in males than females, is one of the most common causes of familial mental retardation. Additional clinical features of this disorder include developmental delay, a long face with a large mandible, large everted ears, and large testicles (macroorchidism). Examination of the DNA from patients with fragile X syndrome reveals multiple tandem repeats of the nucleotide sequence CGG on the X chromosome. Normally these repeats average up to 50 in number, but in patients with fragile X syndrome there are more than 230 repeats. This number of repeats is called a full mutation. Normal transmitting males (NTMs) and carrier females have between 50 and 230 CGG repeats. This number of repeats is called a premutation. During oogenesis, but not spermatogenesis, premutations can be converted to mutations by amplification of the triplet repeats. This explains the much higher incidence of mental retardation in grandsons rather than brothers of normal transmitting males (Sherman’s paradox), as the premutation is amplified in females but not in males. Since the premutation is not amplified in males, no daughters of NTMs are affected. An additional finding associated with these repeat units is anticipation, which refers to the fact that the disease is worse in subsequent generations. 3-22. The answer is b. (Levinson, pp 302–303.) The figure presented in the question shows a Cryptosporidium oocyst stained with a fluorescentlabeled specific antibody. Cryptosporidium may also be stained with a modified acid-fast stain but are not acid-fast bacilli. They are smaller than Cyclospora, which are yeast size, but larger than Enterocytozoon, one of the microsporidia. 3-23. The answer is a. (Hardman, pp 705–706.) Patients at increased risk of developing hyperkalemia should not receive K-sparing diuretics. Potassium-sparing diuretics appear to block Na channels in the luminal membrane of the late distal tubules and the collecting duct. A mild excretion of Na occurs because of the relatively low capacity to reabsorb it in this portion of the nephron. Loop diuretics and thiazides typically increase K excretion.
  • Block 3 Answers 227 3-24. The answer is d. (Cotran, pp 562–563.) Cardiac rupture, whether of free wall, septum, or papillary muscle, occurs in only 1 to 5% of cases following acute myocardial infarction. It occurs usually within the first week of infarction, when there is maximal necrosis and softening (4 to 5 days) and is very rare after the second week. Rupture of the free wall results in pericardial hemorrhage and cardiac tamponade. Rupture of the interventricular septum causes a left-to-right shunt. Serious mitral valve incompetence results from rupture of anterior or posterior papillary muscles. This valve incompetence can produce signs of mitral regurgitation, including a new pansystolic murmur along with a diastolic flow murmur. Indeed, the onset of a new murmur following a myocardial infarction should raise the possibility of papillary rupture. Other common complications of myocardial infarction include arrhythmias such as heart block, sinus arrhythmias, or ventricular tachycardia or fibrillation. These occur in 90% of complicated cases. Next in importance, but not in frequency (only 10%), is cardiogenic shock from severe left ventricular contractile incompetence. Milder left ventricular failure with lung edema occurs in 60% of these cases, while mural thrombosis with peripheral emboli may occur in up to 40%. Ventricular aneurysm forms a “bulge” of the left ventricular chamber; it consists of scar tissue and does not rupture, but may contain a thrombus. Sudden cardiac death occurs within 2 h in 20% of patients with acute myocardial infarction. 3-25. The answer is e. (Murray, pp 307–346. Scriver, pp 2007–2056. Sack, pp 121–138. Wilson, pp 287–317.) In the synthesis of cysteine, the following sequence of steps occurs, where SAM is S-adenosylmethionine, CS is cystathionine synthase, cys is cysteine, and α-KG is α-ketoglutarate: methionine → SAM → homocysteine + adenosine homocysteine + serine → cystathionine → cys + α-KG + NH4+ (CS, B6) Cystathionine synthetase, a pyridoxal phosphate (vitamin B6) enzyme, catalyzes the condensation of serine and homocysteine to form cystathionine. A deficiency of this enzyme leads to a buildup of homocysteine, which oxidizes to form homocystine. This may result in mental retardation, but sometimes causes dislocated lenses and a tall, asthenic build reminiscent of Marfan’s
  • 228 Clinical Vignettes for the USMLE Step 1 syndrome. Patients with homocystinuria also have a clotting diathesis, requiring care to avoid dehydration during anesthesia. Their cysteine deficiency must be made up from dietary sources. In some cases, dietary intake of vitamin B6 (pyrixodal phosphate) may alleviate symptoms because of its requirement by the crucial enzymes. 3-26. The answer is a. (Ash, pp 160–163.) The febrile paroxysms of Plasmodium malariae malaria occur at 72-h intervals; those of P falciparum and . P vivax malaria occur every 48 h. The paroxysms usually last 8 to 12 h with . P vivax malaria but can last 16 to 36 h with P falciparum disease. In P vivax, . . . P ovale, and P malariae infections, all stages of development of the organ. . isms can be seen in the peripheral blood; in malignant tertian (P falciparum) . infections, only early ring stages and gametocytes are usually found. 3-27. The answer is c. (Murray, pp 48–62. Scriver, pp 3–45. Sack, pp 1–3. Wilson, pp 101–120.) In the technique of polyacrylamide gel electrophoresis (PAGE), the distance that a protein is moved by an electrical current is proportional to its charge and inversely proportional to its size. Patients with normal hemoglobin A have two α-globin and two β-globin chains, each encoded by a pair of normal globin alleles. Mutation in one α- or β-globin allele alters the primary amino acid sequence of the encoded globin peptide. If the amino acid change alters the charge of the peptide, then the hemoglobin tetramer assembled with the mutant globin peptide has a different charge and electrophoretic migration than the normal hemoglobin tetramer. The electrophoresis of native (undenatured) hemoglobin therefore produces two species (two bands) rather than one, each retaining its heme molecule and red color. If the hemoglobins were first denatured into their α-globin and β-globin chains as with SDS-polyacrylamide gel electrophoresis, then the similar size of the α- or β-globin peptides would cause them to move closely together as two colorless bands. Identification of these peptides as globin would require use of labeled antibody specific for globin (western blotting). Since the sodium dodecyl sulfate (SDS) detergent covers the protein surface and causes all proteins to be negatively charged, the distance migrated is solely dependent (inversely proportional) to protein size. High-performance liquid chromatography (HPLC) uses ionic resins to separate proteins by charge. The columns are run under high pressure, rapidly producing a series of proteins that are separated from most negative to most positive (or vice versa, depending on the charge of the ionic resin). A mutant
  • Block 3 Answers 229 hemoglobin with altered charge should produce a second red protein in the pattern. In dialysis, semipermeable membranes allow smaller proteins to diffuse into the outer fluid, but not larger proteins such as hemoglobin. 3-28. The answer is e. (Guyton, pp 742–744, 768–769.) Analysis of serum electrolytes reveals low potassium (hypokalemia), low chloride (hypochloremia), and metabolic alkalosis. These abnormalities arise from two sources. First, gastric juice contains potassium and chloride in concentrations higher than found in the plasma. Loss of gastric juice through vomiting or drainage leads to depletions of these electrolytes from the plasma. Second, the metabolic abnormalities are exacerbated by the student’s dehydration. Contraction of the vascular volume leads to orthostatic hypotension and the activation of renal mechanisms important for conserving volume. As a result, water, sodium, and bicarbonate are reabsorbed at the expense of increased potassium and hydrogen excretion. 3-29. The answer is b. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp 97–158. Wilson, pp 23–39.) Albinism is one of many genetic diseases that exhibit locus heterogeneity, which means that mutations at several different loci can produce identical phenotypes. The two McKusick numbers provide a clue that there is more than one locus for albinism, both causing autosomal recessive disease. Each parent must be homozygous for a mutant allele from one albinism locus but heterozygous or homozygous normal at the other locus. Their child would then be an obligate carrier for each type of albinism. A new mutation in the child is also possible, converting one of the parental mutant alleles to normal, but this would be very rare. Autosomal dominant disorders often vary in severity within families (variable expressivity) but occasionally are clinically silent in a person known to carry the abnormal allele (incomplete penetrance). 3-30. The answer is b. (Cotran, pp 1055–1056. Rubin, pp 991–992.) Dysfunctional uterine bleeding (DUB) is defined as abnormal uterine bleeding that is due to a functional abnormality rather than an organic lesion of the uterus. In contrast, secondary dysmenorrhea refers to painful menses associated with an organic cause, such as endometriosis, which is the most common cause. Most cases of DUB are related to an endocrine abnormality affecting the hypothalamic-pituitary-ovarian axis. The three main categories of DUB are anovulatory cycles (the most common form), inad-
  • 230 Clinical Vignettes for the USMLE Step 1 equate luteal phase, and irregular shedding. Anovulatory cycles consist of persistence of the Graafian follicle without ovulation. This results in continued and excess estrogen production without the normal postovulatory rise in progesterone levels. With no progesterone production, no secretory endometrium is formed. Instead, biopsies reveal nonsecretory (proliferative) endometrium with mild hyperplasia. The mucosa becomes too thick and is sloughed off, resulting in the abnormal bleeding. Anovulatory cycles characteristically occur at menarche and menopause. They are also associated with polycystic ovary (Stein-Leventhal) syndrome. It is important to note that other causes of unopposed estrogen effect can lead to this appearance of a proliferative endometrium with mild hyperplasia. These causes include exogenous estrogen administration or estrogen-secreting neoplasms, such as a granulosa cell tumor of the ovary or an adrenal cortical neoplasm. If there is ovulation but the functioning of the corpus luteum is inadequate, then the levels of progesterone are decreased, resulting in asynchrony between the chronologic dates and the histologic appearance of the secretory endometrium. This is referred to as an inadequate luteal phase (luteal phase defect) and is an important cause of infertility. Biopsies are usually performed several days after the predicted time of ovulation. If the histologic dating of the endometrium lags 4 or more days behind the chronologic date predicted by the menstrual history, the diagnosis of luteal phase defect can be made. Clinically, these patients exhibit low serum progesterone, FSH, and LH levels. In contrast, prolonged functioning of the corpus luteum (persistent luteal phase with continued progesterone production) results in prolonged heavy bleeding at the time of menses. Histologically, there is a combination of secretory glands mixed with proliferative glands (irregular shedding). Clinically, these patients have regular periods, but the menstrual bleeding is excessive and prolonged (lasting 10 to 14 days). Current oral contraceptives, being a combination of estrogen and progesterone, cause the endometrium to include inactive glands with predecidualized stroma. The endometrium in postmenopausal women reveals an atrophic pattern with atrophic or inactive glands. 3-31. The answer is e. (Sweeney, pp 14–15, 91, 108, 122, 154. Moore, Developing Human, pp 189, 435.) Vitamin A is a member of the retinoic acid family. Retinoic acid directs the polarity of development in the central nervous system, the axial skeleton (vertebral column), and probably the
  • Block 3 Answers 231 appendicular skeleton as well. Retinoic acid turns on various combinations of homeobox genes, depending on tissue type and location (distance and direction from the source of retinoic acid). Exogenous sources of retinoic acid may induce the wrong sequence or combination of homeobox genes, leading to structural abnormalities in the nervous and skeletal systems. The other organ systems listed are not as susceptible to vitamin A. 3-32. The answer is d. (Katzung, p 940. Hardman, p 1267.) The potential serious adverse effect of bleomycin is pneumonitis and pulmonary fibrosis. This adverse effect appears to be both age- and dose-related. The clinical onset is characterized by decreasing pulmonary function, fine rales, cough, and diffuse basilar infiltrates. This complication develops in approximately 5% to 10% of patients treated with bleomycin. Thus, extreme caution must be used in patients with a preexisting history of pulmonary disease. All of the other drugs listed in the question are effective against carcinomas and have not been associated with significant lung toxicity. 3-33. The answer is b. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp 97–158. Wilson, pp 361–391.) Succinylcholine is metabolized by a plasma enzyme formerly called pseudocholinesterase [now called butyrylcholinesterase (BChE) to designate its favored substrate]. Approximately 1 in 100 individuals are homozygous for a variant of BChE that has 60% activity, while 1 in 150,000 individuals are homozygous for a variant with 33% activity. The latter group exhibits prolonged recovery from succinylcholineinduced anesthesia, a phenotype known as succinylcholine apnea. As with most enzyme defects, succinylcholine apnea exhibits autosomal recessive inheritance. The father is presumably homozygous for a BChE variant, like his two deceased siblings, but has not undergone anesthesia to display the phenotype. His daughter is also likely to be homozygous, implying that her mother is a heterozygote. (Note that the BChE variant with 60% activity has a heterozygote frequency of 1/5 by application of the Hardy-Weinberg law.) 3-34. The answer is c. (Braunwald, p 985.) The rash is impetigo, which is caused by group A streptococci, occasionally by other streptococci, and also by Staphylococcus aureus. It occurs in children who have poor hygiene, and the streptococci, which colonize the skin, gain entrance through a break in the skin, such as a scratch or an insect bite. The rash is painless, unlike herpes simplex or shingles, which is due to Herpesvirus varicellae.
  • 232 Clinical Vignettes for the USMLE Step 1 Herpes simplex occurs on the face and mouth and genitals; shingles follows the distribution of a nerve, mainly the temporal nerve and the intracostal nerves. Scarlet fever, also due to streptococci, characteristically covers the trunk and extremities with a fine papular rash, sparing the palms and soles. Erysipelas is a streptococcal cellulitis. 3-35. The answer is d. (Howard, pp 755–756.) Hepatitis E virus (HEV) is a single-stranded RNA virus. It is transmitted enterically, and the disease is often referred to as enteric hepatitis C. There is no test for HEV routinely available. Diagnosis is clinical and also one of exclusion. 3-36. The answer is e. (Taylor, pp 418–424.) Of the psychological defense mechanisms listed, denial is the most common. Most defense mechanisms involve an unconscious mental process and are protective measures for the relief of anxiety or guilt. In denial, the patient attempts to reject the threat of the perception of illness and the developing anxiety. While failure to face one’s illness can be harmful, denial can also be a useful defense mechanism, especially during recovery or rehabilitation. In rationalization, a patient attempts to justify an irrational feeling, behavior, or thought. Projection involves attributing one’s own problem or conflict to another person or situation. In displacement, a feeling, thought, wish, or fear that is unacceptable is transferred to another person or situation. Sublimation is a defense mechanism whereby wishes that are unacceptable are diverted into acceptable channels; thus partial gratification is achieved. 3-37. The answer is b. (Gilroy, p 337; Kandel, pp 951–953.) Sleep apnea can occur for several reasons. One common basis is an obstruction of the airways (called obstructive sleep apnea). In this case, as indicated in the statement of the question, the physicians ruled out this possibility. Another possible cause involves central sleep apnea. This is due to disruption of the mechanism involving chemoreceptors in the carotid body that monitors carbon dioxide and oxygen levels in the blood. Axons in the carotid body project via the glossopharyngeal nerve (IX) to the reticular formation of the medulla. Therefore, disturbances involving the carotid body could result in central sleep apnea. Here, inappropriate signals are sent to the medullary reticular formation, which, in part, projects caudally to ventral horn sites in the spinal cord, governing such muscles as those that regulate the diaphragm and, therefore, disrupt the normal breathing process.
  • Block 3 Answers 233 3-38. The answer is d. (Moore, Developing Human, pp 22–23.) In man the time required for the progression from spermatogonium to motile spermatozoon is about two months (61 to 64 days). Spermatogenesis, the process by which spermatogonia undergo mitotic division to produce primary spermatocytes, occurs at 1°C (2°F) below normal body temperature. Subsequent meiotic divisions produce secondary spermatocytes with a bivalent haploid chromosome number and then spermatids with a monovalent haploid chromosome number. The maturation of the spermatid, spermiogenesis, results in spermatozoa. Morphologically adult spermatozoa are moved to the epididymis where they become fully motile. 3-39. The answer is d. (Hardman, pp 701–702, 704. Katzung, p 741.) Hydrochlorothiazide is recommended in the treatment of idiopathic hypercalciuria because of its ability to decrease the excretion of Ca. The loop diuretics are contraindicated because they increase urinary Ca excretion. The mechanism for decreased Ca excretion by the thiazides is not known, but it is thought that inhibition of NaCl co-transport in the distal tubules by thiazides causes membrane depolarization. This results in the opening of the Ca channels followed by the reabsorption of Ca. 3-40. The answer is b. (Kandel, p 544; Nolte, pp 422–424.) This large pituitary tumor is seen to compress the optic chiasm. Damage to the chiasm affects the crossing fibers of the nasal retina, which convey information from the temporal visual fields. This results in a bitemporal hemianopsia. Since some parts of the optic nerves are spared, pupillary reflexes are preserved. The neuroanatomic substrates for conjugate gaze (i.e., frontal eye fields; pontine gaze center; medial longitudinal fasciculus; and nuclei of cranial nerves III, IV, and VI) are unaffected by the tumor; the mechanism of conjugate gaze remains intact. 3-41. The answer is b. (Baum, pp 306–310.) Biofeedback is a process of learning to control various components of one’s autonomic responses by using visual or auditory feedback of information from one’s physiologic functions. The feedback of information about one’s physiologic responses and one’s ability to learn and practice control can be influenced by such factors as motivation, feelings, attitude, and interpersonal relations, but information feedback is the primary component in the learning process. Just as one learns to improve one’s motor skills by feedback of information and
  • 234 Clinical Vignettes for the USMLE Step 1 observations of distance, time, space, improvement, and so on, one can learn to exert influence on physiologic responses. Formerly these physiologic responses had been regarded as autonomic because we had no visual electronic or mechanical mechanism for feeding back such information. 3-42. The answer is c. (Cotran, pp 1029–1033.) Knowledge of the anatomic division of the prostate is important in understanding the locations of the major pathologic diseases of the prostate. Most adenocarcinomas of the prostate originate in the peripheral zone, while hyperplastic nodules originate in the transition zone. This anatomic differentiation is the result of the physiologic fact that the transition zone is particularly estrogen-sensitive, while the peripheral zone is particularly androgensensitive. Dihydrotestosterone (DHT), which is formed from testosterone by the action of 5-α-reductase, is responsible for the development of the prostate during fetal growth and also at the time of puberty. With aging, DHT levels are increased in the prostate, where DHT binds to nuclear DNA and causes prostatic hyperplasia. This hyperplastic effect by DHT is augmented by estrogen, which appears to function by induction of androgen receptors, and therefore this hyperplasia occurs in the portion of the prostate that is particularly estrogen-sensitive. 3-43. The answer is a. (Baum, pp 99, 173–174.) Bereavement from the loss of a loved one has been found to reduce the responsiveness of lymphocytes to mitogens. The same reaction occurs as a result of certain lifestyle factors, such as cigarette smoking and alcohol consumption. Psychological and social stress not only suppresses the immune system, but also suppresses DNA synthesis and DNA repair. Lack of close personal or family ties has been associated with reduced immune competence and with tumor growth. Environmental, physiologic, and psychosocial factors are thought to trigger the development and growth of cancer by suppressing the “surveillance” function of the immune system, which protects the body from invasion of alien cells and viruses. Exercise improves normal bodily functions, so the usual defense mechanisms should help protect against rather than enhance tumor growth. 3-44. The answer is e. (McPhee, pp 531–535. Braunwald, pp 2105–2107.) Hypothyroid patients tend to gain weight. Prolactin-secreting tumors (prolactinomas), being located in the pituitary, would be expected to show
  • Block 3 Answers 235 abnormal physical examination findings at the eyes, given that the tumor typically sits on the optic chiasma. Early menopause is unlikely in a 22year-old. Resistance to LH and FSH would have prohibited this patient from ever having menses. This leaves excessive exercise as the only remaining plausible cause in this patient. 3-45. The answer is e. (Howard, p 860.) While the essential information (i.e., the evidence that the child in question was scratched by a cat) is missing, the clinical presentation points to a number of diseases, including catscratch disease (CSD). Until recently, the etiologic agent of CSD was unknown. Evidence indicated that it was a pleomorphic, rod-shaped bacterium that had been named Afipia. It was best demonstrated in the affected lymph node by a silver impregnation stain. However, it now appears that Afipia causes relatively few cases of CSD and that the free-living rickettsia primarily responsible is Rochalimaea henselae, which has recently been renamed Bartonella henselae. 3-46. The answer is b. (Moore & Dalley, pp 187, 191, 205–207.) The ilioinguinal nerve innervates the portion of the internal oblique muscle inserting in the lateral border of the conjoint tendon. Paralysis of these fibers would create weakness in the conjoint tendon, allowing herniation to occur medial to the inferior epigastric vessels. The genitofemoral nerve supplies sensory innervation to the skin of the femoral triangle and scrotum/labia majora. The subcostal nerve (T12) supplies lower portions of the external abdominal oblique muscle. The pelvic splanchnic nerves supply autonomic (parasympathetic) innervation to the pelvic viscera. The tenth thoracic spinal nerve (T10) supplies abdominal muscles superior to the inguinal region. 3-47. The answer is a. (Hardman, p 221. Katzung, p 131.) Methylphenidate is similar to amphetamine and acts as a CNS stimulant, with more pronounced effects on mental than on motor activities. It is effective in the treatment of narcolepsy and attention-deficit hyperactivity disorders. 3-48. The answer is a. (Moore, Developing Human, p 276.) Blockage of the foregut in the newborn produces projectile vomiting. Congenital hypertrophic pyloric stenosis, occurring in 0.5 to 1.0% of males and rarely in females, involves hypertrophy of the circular layer of muscle at the
  • 236 Clinical Vignettes for the USMLE Step 1 pylorus. This usually does not regress and must be treated surgically. During the fifth and sixth weeks of development, the lumen of the duodenum is occluded by muscle proliferation but normally recanalizes during the eighth week. Failure of recanalization results in duodenal atresia. Because this occurs distal to the hepatopancreatic ampulla, the vomitus will occasionally be stained with bile. Annular pancreas, rare in itself, seldom completely blocks the duodenum. Imperforate anus results in intestinal distention with bloating. 3-49. The answer is a. (Murray, pp 1217–1225.) While all fungi such as Candida and Cryptococcus are potentially serious in a bone marrow transplant unit (BMTU), the most frequent cause of fungal infection and death is Aspergillus. Aspergilli are ubiquitous in the environment. There are instances of multiple infections in new units that have not been monitored prior to opening or in units adjacent to construction projects. Strict precautions should be taken to exclude dust and debris from the BMTU area during construction, but in any event the environment should be monitored for airborne microorganisms, especially Aspergillus, prior to opening the unit. 3-50. The answer is c. (Braunwald, p 270.) Lithium therapy results in nephrogenic diabetes insipidus. These patients maintain a high normal serum osmolarity unless water intake is restricted because the thirst center is intact and able to regulate serum osmolarity by water intake. They develop hypernatremia if they are hospitalized or develop CNS problems.
  • BLOCK 4 Answers 4-1. The answer is a. (Cotran, pp 516, 521–522. Rubin, pp 515–516. Damjanov, pp 1429–1431.) Leukocytoclastic angiitis refers to the histologic finding of fragmented neutrophils surrounding small blood vessels. The differential diagnosis of leukocytoclastic vasculitis includes microscopic polyarteritis nodosa and three other disorders: Henoch-Schönlein purpura, Wegener’s granulomatosis, and Churg-Strauss syndrome. HenochSchönlein purpura is a disorder of children who present with hemorrhagic urticaria and hematuria following an upper respiratory infection. The pathology of this disease involves the deposition of IgA immune complexes in small vessels of the skin. Because the antibody is IgA, the alternate complement pathway is activated in these patients. Wegener’s granulomatosis (WG) is characterized by acute necrotizing granulomas of the upper and lower respiratory tract, focal necrotizing vasculitis affecting small to medium-sized vessels, and renal disease. Histologically there is fibrinoid necrosis of small arteries, early infiltration by neutrophils, and granuloma formation with giant cells. The peak incidence is in the fifth decade, and many patients have C-ANCAs. The disease is highly fatal, with death occurring within 1 year, unless recognized and treated with immunosuppressive agents. Churg-Strauss syndrome (allergic vasculitis) is a form of necrotizing vasculitis with granulomas of the respiratory tract and asthma. The disorder is associated with increased serum IgE and peripheral eosinophilia. 4-2. The answer is c. (McPhee, pp 530, 539. Braunwald, pp 812–817.) Pelvic inflammatory disease is a cause of tubal scarring, setting the stage for an ectopic (tubal) pregnancy. As the pregnancy grows, the tube is stretched, causing pain. Endometriosis causes pain with each menstrual cycle, which is not the case here. Urinary tract infection can cause pain, but she would be expected to have dysuria. Placental abruption occurs only after 20 weeks of pregnancy. She is clearly not premenstrual, because she is pregnant. 237 Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  • 238 Clinical Vignettes for the USMLE Step 1 4-3. The answer is e. (Berne, 3/e, pp 258–260.) When a person rises suddenly, blood pools in the dependent portions of the body, causing decreases in venous return, left ventricular end-diastolic volume, stroke volume, and pulse pressure. The reduced stroke volume leads to a drop in cardiac output and, therefore, a drop in blood pressure. Decreased blood pressure produces the baroreceptor reflex, leading to an increase in sympathetic activity, which increases total peripheral resistance, cardiac contractility, heart rate, and ejection fraction. These changes in the cardiovascular system return blood pressure toward normal. 4-4. The answer is c. (Moore & Dalley, pp 731, 742, 761.) All of the muscles listed are innervated by the posterior interosseus branch of the radial nerve (the terminal part of the deep radial nerve). Extensor carpi radialis longus, however, is innervated by a muscular branch of the radial nerve proximal to the origin of the deep branch. Its function would, therefore, be preserved in entrapment of the posterior interosseus nerve. 4-5. The answer is e. (Moore & Dalley, pp 731, 742, 761.) Each of the muscles listed is innervated by the deep branch of the radial nerve or its terminal portion, the posterior interosseus nerve. The deep radial nerve passes between the deep and superficial layers of the supinator muscle and lies on a bare area of the radius where it may be compressed by action of the supinator or damaged by a fracture of the radius. 4-6. The answer is d. (Hardman, p 564. Katzung, pp 370, 1013.) Flumazenil is a competitive antagonist of benzodiazepines at the GABA receptor. Repeated administration is necessary because of its short half-life relative to that of most benzodiazepines. 4-7. The answer is c. (Cotran, pp 670–675.) The diagnosis of Hodgkin’s disease depends on the clinical findings added to the total histologic picture, which includes the presence of binucleated or bilobed giant cells with prominent acidophilic “owl-eye” nucleoli known as Reed-Sternberg (RS) cells. However, cells similar in appearance to RS cells may also be seen in infectious mononucleosis, mycosis fungoides, and other conditions. Thus, while RS cells are necessary for histologic confirmation of the diagnosis of Hodgkin’s disease, they must be present in the appropriate histologic setting of lymphocyte predominance, nodular sclerosis, mixed cellularity, or lymphocyte
  • Block 4 Answers 239 depletion to make the correct diagnosis. In contrast, Call-Exner bodies are seen in granulosa cell tumors of the ovary, Hürthle cells are associated with Hashimoto’s thyroiditis, Sézary cells are associated with mycosis fungoides, and strap cells are seen in skeletal muscle tumors, such as rhabdomyomas. 4-8. The answer is c. (Hardman, p 1302.) Muromonab-CD3 is a monoclonal antibody that interferes with T cell function. It is classified as an immunosuppressive drug. This drug is given intravenously and is indicated in the treatment of acute allograft rejection. Generally, azathioprine and prednisone are used along with muromonab-CD3. Interferon α and aldesleukin (interleukin 2) are cytokines that are classified as immunostimulants. Sargramostim and filgrastim are also immunostimulants. These drugs are produced by recombinant DNA technology. Sargramostim is a human granulocyte-macrophage colony stimulating factor (GM-CSF), and filgrastim is a human granulocyte colony stimulating factor (G-CSF). 4-9. The answer is e. (Afifi, pp 209–213.) The cranial nerve involved in adduction of the eye is cranial nerve III, in which the act of moving the eye medially is governed by the medial rectus muscle. Cranial nerve III is located near the midline of the rostral half of the midbrain just below the midbrain periaqueductal gray. 4-10. The answer is e. (Baum, pp 363–372.) Evaluations of treatment methods using the classical conditioning model have demonstrated that relapse is more likely to occur in the presence of alcohol-associated stimuli. Thus, the most effective treatment conditions should maintain an environment that is as free as possible of alcohol-associated stimuli, and the patient should be returned to an environment that is different from the one in which dependence was acquired. Since dependence is acquired by the patient’s developing alcohol-compensatory conditioned responses, specific, therapeutic strategies should be implemented and practiced over time prior to discharge to extinguish these alcohol-compensatory conditioned responses. Aversive affective states, such as depression or anxiety, can also act to increase the likelihood of relapse, so all treatment procedures should attempt to extinguish conditioned associations between aversive affective states and alcohol. The patient will probably experience relief from withdrawal symptoms if allowed to substitute other drugs; thus the very conditioned responses targeted for extinction will be maintained.
  • 240 Clinical Vignettes for the USMLE Step 1 4-11. The answer is b. (Moore & Dalley, p 299.) Tuberculous infections of the lumbar vertebrae are frequently communicated to the sheath of the adjacent psoas muscles. Subsequently, pus may travel inferiorly over the pelvic brim and erupt on the anterior thigh near the insertion of the psoas on the lesser trochanter of the femur. Abscesses in the ischiorectal fossae may drain into the pelvis or the anal canal. The inguinal ligament passes laterally to medially superficial to the psoas muscle to transmit contents to the scrotum or labia. Its origin in the anterolateral abdominal wall is not in close approximation to the lumbar vertebrae. The paracolic gutters can spread infection or metastases into the pelvis or the subphrenic region, depending on whether the patient is erect or supine. 4-12. The answer is e. (Katzung, pp 141, 168.) Prazosin blocks α1-adrenergic receptors in arterioles, thereby decreasing peripheral resistance and leading to a decrease in blood pressure. Orthostatic hypotension can occur, particularly after a first dose. 4-13. The answer is d. (Braunwald, p 1549.) Urine dipstick cannot detect light chains and Bence Jones proteins found in paraproteinemias. So there is a discrepancy between dipstick values and the 24-h urine collection. The sulfosalicylic acid test (SSA) can precipitate all proteins and can be diagnostic as well. Focal sclerosis and amyloidosis would not have this discrepancy. Hypertensive nephrosclerosis presents with milder degrees of proteinuria. 4-14. The answer is d. (Guyton, pp 428–429.) Hemostasis following blood vessel injury depends on (1) vascular spasm, (2) formation of a platelet plug, and (3) clot formation. When injury to a vessel produces only a small defect, the platelet plug itself can cause hemostasis. This is the basis for the bleeding time that is employed clinically to distinguish hemostatic abnormalities caused by platelet abnormalities from those caused by coagulation defects. Aspirin diminishes platelet aggregation by inhibiting cyclooxygenase, an enzyme required for generation of thromboxanes, which promote platelet aggregation. All the other situations described in the question are associated with coagulation deficiency. Persons thus affected would have a normal bleeding time but would present clinically with delayed posttraumatic bleeding caused by their inability to form an effective clot to reinforce the platelet plug.
  • Block 4 Answers 241 4-15. The answer is b. (Murray, pp 230–267. Scriver, pp 2297–2326. Sack, pp 121–138. Wilson, pp 287–320.) Untreated ethylene glycol of antifreeze can be converted to the kidney toxin oxalate crystals. This occurs by oxidation of ethylene glycol. The first committed step in this process is the oxidation of ethylene glycol to an aldehyde by alcohol dehydrogenase. This is normally the route for converting ethanol (drinking alcohol) to acetate. Patients who have ingested ethylene glycol or wood alcohol (methanol) are placed on a nearly intoxicating dose of ethanol by a nasogastric tube together with intravenous saline and sodium bicarbonate. This treatment is carried out intermittently along with hemodialysis until no traces of ethylene glycol are seen in the blood. Ethanol acts as a competitive inhibitor of alcohol dehydrogenase with respect to ethylene glycol or methanol metabolism. 4-16. The answer is b. (Howard, pp 819–821.) The highest risk of fetal infection with rubella occurs during the first trimester. In seronegative patients, the risk of infection exceeds 90%. However, before other measures (such as termination of pregnancy) are considered, a rubella immune status must be performed. A rubella titer of 1:10 is protective. 4-17. The answer is d. (Cotran, pp 683–685.) Myeloid metaplasia with myelofibrosis is a myeloproliferative disorder in which the bone marrow is hypocellular and fibrotic and extramedullary hematopoiesis occurs, mainly in the spleen (myeloid metaplasia). Marked splenomegaly with trilineage proliferation of normoblasts, immature myeloid cells, and large megakaryocytes occur. Giant platelets and poikilocytic (teardrop) red cells are seen in the peripheral smear. Clinically, myeloid metaplasia may be preceded by polycythemia vera or chronic myeloid leukemia. Biopsy of the marrow is essential for diagnosis. In contradistinction to chronic myeloid leukemia, levels of leukocyte alkaline phosphatase are elevated or normal in myeloid metaplasia; in CML, levels are low or absent. In 5 to 10% of cases of myeloid metaplasia, acute leukemia occurs. In aplastic anemia the marrow is very hypocellular, but consists largely of fat cells, not fibrosis. There is no splenomegaly. Microangiopathic and other hemolytic anemias that result from trauma to red cells show many erythrocytic abnormalities (helmet and burr cells, triangle cells, and schistocytes) in the peripheral smear. 4-18. The answer is d. (Hardman, p 1346.) Heparin is a mixture of sulfated mucopolysaccharides and is highly acidic and highly charged. Pro-
  • 242 Clinical Vignettes for the USMLE Step 1 tamine is a very basic polypeptide that combines with heparin. The complex has no anticoagulant activity. Excess protamine does have anticoagulant activity, so just enough should be given to counteract the heparin effect. 4-19. The answer is a. (Murray, pp 230–267. Scriver, pp 3827–3876. Sack, pp 121–138. Wilson, pp 287–320.) Gangliosides are continually synthesized and broken down. The specific hydrolases that degrade gangliosides by sequentially removing terminal sugars are found in lysosomes. In the lipid storage disease known as Tay-Sachs disease (272800), ganglioside GM2 accumulates because of a deficiency of β-N-acetylhexosaminidase, a lysosomal enzyme that removes the terminal N-acetylgalactosamine residue. Homozygotes produce virtually no functional enzyme and suffer weakness, retardation, and blindness. Death usually occurs before infants are 3 years old. Carriers (heterozygotes) of the autosomal recessive disease produce approximately 50% of the normal levels of enzyme but show no ill effects. In high-risk populations, such as Ashkenazi Jews, screening for carrier status may be performed. 4-20. The answer is d. (Braunwald, p 1547.) All of these diseases are common in older persons. Amyloidosis and light chain deposition disease are related to paraprotein deposition in the kidney and typically present with nephrotic syndrome. The subacute presentation and erythrocyte casts in the urine along with the rapid decline in renal function are most consistent with vasculitis. A positive antineutrophil cytoplasmic antibody (ANCA) would be supportive. Erythrocyte casts are not seen in the other diseases. 4-21. The answer is d. (Hardman, pp 1676–1678. Katzung, pp 990–991.) Carbon monoxide is a common cause of accidental and suicidal poisoning. Its affinity for hemoglobin is 250 times greater than that of O2. It therefore binds to hemoglobin and reduces the O2-carrying capacity of blood. The symptoms of poisoning are due to tissue hypoxia; they progress from headache and fatigue to confusion, syncope, tachycardia, coma, convulsions, shock, respiratory depression, and cardiovascular collapse. Carboxyhemoglobin levels below 15% rarely produce symptoms; above 40%, symptoms become severe. Treatment includes establishment of an airway, supportive therapy, and administration of 100% O2. Sulfur dioxide, ozone, and nitrogen dioxide are mucous membrane and respiratory irritants. Methane is a simple asphyxiant.
  • Block 4 Answers 243 4-22. The answer is a. (April, pp 359–360.) Visceral afferent pain fibers from the gallbladder travel through the celiac plexus, thence along the greater splanchnic nerves to levels T5–T9 of the spinal cord. Thus, pain originating from the gallbladder will be referred to (appear as if coming from) the dermatomes served by T5–T9, which include a band from the infrascapular region to the epigastrium. 4-23. The answer is a. (Moore & Dalley, pp 182–186.) The rectus sheath is formed by the aponeuroses of the abdominal wall musculature. Between the costal margin and the umbilicus, the aponeurosis of the internal oblique muscle splits; one portion passes anterior and the other posterior to the rectus abdominis muscle. The aponeurosis of the external oblique muscle fuses with the anterior leaflet of the aponeurosis of the internal oblique muscle to form the anterior wall of the rectus sheath. The aponeurosis of the transversus abdominis muscle fuses with the posterior leaflet of the aponeurosis of the internal oblique muscle to form the posterior wall of the rectus sheath. Approximately midway between the umbilicus and symphysis pubis, the aponeuroses of the internal oblique and transversus abdominis muscles pass anterior to the rectus abdominis muscle to contribute to the anterior leaf of the rectus sheath. This abrupt transition results in a free edge to the posterior rectus sheath, known as the arcuate line (of Douglas). Between this line and the pubis, only the transversalis fascia separates the rectus abdominis muscle from the peritoneum. It is here, where the inferior epigastric artery gains access to the rectus sheath, that ventral lateral (spigelian) herniation may occur. 4-24. The answer is b. (Hardman, p 1299. Katzung, p 609.) Nephrotoxicity may occur in almost three-quarters of patients treated with cyclosporine. Regular monitoring of blood levels can reduce the incidence of adverse effects. 4-25. The answer is a. (Cotran, pp 1025–1027.) Inflammation of the prostate (prostatitis) is characterized by finding at least 15 leukocytes per high-power field in prostatic secretions. Prostatitis is classified as being either acute or chronic. Patients with acute prostatitis present with the sudden onset of fever, chills, and dysuria. Acute prostatitis is usually caused by bacteria that cause urinary tract infections, such as Escherichia coli. Chronic prostatitis presents clinically as low back pain, dysuria, and suprapubic discomfort. It is divided into chronic bacterial prostatitis, which is associated with recurrent urinary tract infections (UTIs) with the same organism,
  • 244 Clinical Vignettes for the USMLE Step 1 and chronic abacterial prostatitis, which is not associated with recurrent UTIs. Instead, chronic abacterial prostatitis is associated with infections with either Chlamydia trachomatis or Ureaplasma urealyticum. Granulomatous prostatitis causes vague symptoms and has an unknown etiology. This diagnosis is made histologically. 4-26. The answer is a. (Cotran, pp 516–518. Rubin, pp 516–517.) Giant cell arteritis (temporal arteritis), although not a major public health problem, is an important disease to consider in the differential diagnosis of patients of middle to advanced age who present with a constellation of symptoms that may include migratory muscular and back pains (polymyalgia rheumatica), dizziness, visual disturbances, headaches, weight loss, anorexia, and tenderness over one or both of the temporal arteries. The cause of the arteritis (which may include giant cells, neutrophils, and chronic inflammatory cells) is unknown, but the dramatic response to corticosteroids suggests an immunogenic origin. The disease may involve any artery within the body, but involvement of the ophthalmic artery or arteries may lead to blindness unless steroid therapy is begun. Therefore, if temporal arteritis is suspected, the workup to document it should be expedited and should include a biopsy of the temporal artery. Frequently, the erythrocyte sedimentation rate (ESR) is markedly elevated to values of 90 or greater. Whereas tenderness, nodularity, or skin reddening over the course of one of the scalp arteries, particularly the temporal, may show the ideal portion for a biopsy, it is important to recognize that the temporal artery may be segmentally involved or not involved at all even when the disease is present. 4-27. The answer is c. (Levinson, pp 147–148.) At the present time, Lyme disease may be diagnosed clinically and serologically. Patients who are from endemic areas such as eastern Pennsylvania and report joint pain and swelling months subsequent to exposure to ticks must be evaluated for Lyme disease and treated if the test is positive. Patients may also report a variety of neurologic problems such as tingling of the extremities, Bell’s palsy, and headache. IgM antibody appears soon after the tick bite (10 days to 3 weeks) and persists for 2 months; IgG appears later in the disease but remains elevated for 1 to 2 years, especially in untreated patients. A significant IgG titer is at least 1:320. Most investigators feel that IgM titers of 1:100 are significant; some investigators say that any IgM titer is significant.
  • Block 4 Answers 245 4-28. The answer is d. (Moore & Dalley, pp 100–103, 162–163.) The lobe indicated by the * is the left upper (or superior) lobe. The general orientation when viewing CTs is that the observer is looking up from the patient’s feet. Therefore, the patient’s left is on your right. In addition, on the left, the inferior (lower) lobe begins relatively high in the thoracic cavity and is posterior to the upper lobe. 4-29. The answer is a. (Hardman, p 1180. Katzung, pp 817–819.) Fluconazole indirectly inhibits ergosterol synthesis. It inhibits cytochrome P450, which is a key enzyme system for cytochrome P450–dependent sterol 14-α-demethylase. This leads to accumulation of 14-α-sterols, resulting in impairment of the cytoplasmic membrane. 4-30. The answer is b. (Baum, pp 157–159.) Fifteen percent of the population (more than 35 million people) in the United States have hypertension. Risk factors for hypertension constitute complex interactions between behavioral, physiologic, and genetic factors. Age, race, and family history have been the standard risk factors, but they are not modifiable. More recently behavioral and environmental factors have been documented to play a significant role in the pathogenesis of hypertension. Of these behavioral risk factors, eating behaviors related to high intake of dietary salt and obesity are most relevant, followed by stress and personality factors, which are again related to a person’s coping mechanisms. The complex interaction of these behavioral factors over time is most significant. Compliance with medical treatment is crucial after hypertension has developed, but not in its pathogenesis. 4-31. The answer is d. (Levinson, pp 287–288.) Eumycotic mycetoma is a slowly progressing disease of the subcutaneous tissues that is caused by a variety of fungi. The term Madura foot has been used to describe the foot lesion. Although several fungi have been isolated in the United States from persons who have mycetoma, Pseudallescheria boydii appears to be one of the most common. Other foot infections that may resemble Madura foot are actinomycotic (bacterial) in nature. These are caused by Nocardia brasiliensis and Actinomadura. 4-32. The answer is e. (Braunwald, p 246.) Hematemesis or vomiting of blood represents an upper gastrointestinal (GI) source of blood loss. Bleed-
  • 246 Clinical Vignettes for the USMLE Step 1 ing from the colon will be manifested by either by no change in the color of the stools or by black, tarry-like stools (melena). Bleeding from the lungs results in blood in the sputum (hemoptysis) and from the kidneys as blood in the urine (hematuria), mainly microscopic hematuria. 4-33. The answer is e. (Murray, pp 298–307. Scriver, pp 1471–1488. Sack, pp 217–218. Wilson, pp 361–384.) In the presence of insulin deficiency, a shift to fatty acid oxidation produces the ketones such as acetoacetate that cause metabolic acidosis. The pH and bicarbonate are low, and there is frequently some respiratory compensation (hyperventilation with deep breaths) to lower the PCO2, as in choice e. A low pH with high PCO2 would represent respiratory acidosis (choices a and b—the low-normal bicarbonate values in these choices indicate partial compensation). Choice d represents respiratory alkalosis as would occur with anxious hyperventilation (high pH and low PCO2, partial compensation with high bicarbonate). Choice c illustrates normal values. 4-34. The answer is b. (Cotran, pp 1222–1224. Chandrasoma, pp 963–966.) Osteopenia (reduction in the amount of bone) is seen in osteoporosis, osteomalacia, and osteitis fibrosa. Osteoporosis is characterized by qualitatively normal bone that is decreased in amount. Histologic bone sections reveal thin trabeculae that have normal calcification and normal osteoblasts and osteoclasts. Osteoporosis predisposes patients to fractures of weight-bearing bones, such as the femurs and vertebral bodies. Patients typically have normal serum levels of calcium, phosphorus, alkaline phosphatase, and parathyroid hormone. Osteoporosis is classified as being primary or secondary. Primary osteoporosis, the most common type of osteoporosis, occurs most often in postmenopausal women and has been related to decreased estrogen levels. Cigarette smoking is also associated with an increased incidence of osteoporosis. Clinically significant osteoporosis is related to the maximum amount of bone a person has (peak bone mass), which is largely genetically determined. Secondary osteoporosis develops secondary to many conditions such as corticosteroid administration, hyperthyroidism, and hypogonadism. In contrast, osteopetrosis is a rare inherited disease characterized by abnormal osteoclasts showing decreased functioning. This abnormality results in reduced bone resorption and abnormally thickened bone. In these patients, multiple fractures are frequent as the bones are structurally
  • Block 4 Answers 247 weak and abnormally brittle. Increased fragility of bones is also present in osteomalacia (caused by abnormal vitamin D metabolism in adults) and osteitis deformans (Paget’s disease). Osteitis fibrosa cystica (von Recklinghausen’s disease of bone) is seen with severe hyperparathyroidism and is characterized by increased bone cell activity, peritrabecular fibrosis, and cystic bone lesions. 4-35. The answer is f. (Katzung, p 972.) Azathioprine is a derivative that is closely related to 6-MP, which is used as a cancer chemotherapeutic agent, while azathioprine is used as an immunosuppressive agent because it is more effective than 6-MP in this regard. Azathioprine is used in organ transplantation, particularly kidney allografts. Like 6-MP, azathioprine is biotransformed to an inactive product by xanthine oxidase. Allopurinol, which inhibits this enzyme, can increase the therapeutic action of azathioprine and possibly its adverse reactions. The dosage of azathioprine should be decreased in the presence of allopurinol. 4-36. The answer is c. (Howard, pp 680–681.) Consumption of raw fish causes endemic diphyllobothriasis in Scandinavia and the Baltic countries. While most people do not become ill, a small percentage (2%) develop vitamin B12 deficiency anemia. The adult fish tapeworm has an affinity for vitamin B12 and may induce a serious megaloblastic anemia. Parvovirus B 19 causes acute hemolytic anemia primarily in immunosuppressed patients. Yersinia infection is common in Scandinavia but is not fish-borne and does not cause anemia. The larval stage of T. solium is called cysticercus. Humans usually acquire cysticercosis by ingestion of food and water contaminated by infected human feces. 4-37 through 4-38. The answers are 4-37 b, 4-38 c. (Kandel, pp 480–484; Siegel, pp 1096–1098.) Research conducted over the past 2 decades has shown that the actions of morphine are mediated through opioid µ receptors, while other opioid receptors appear not to play a significant role. Likewise, dopamine receptors are not involved in this process. The region of the brain where concentrations of opioid receptors are very heavily concentrated is the midbrain periaqueductal gray. This region plays an important role in the modulation of pain and is particularly responsive to opioid activation by morphine. While other areas of the brain indicated in question 4-37 may also contain opioid receptors, concentrations of this
  • 248 Clinical Vignettes for the USMLE Step 1 receptor are not known to be high (including a structure such as the mammillary bodies for which no known functions have been identified). Moreover, none of these regions are known to play any role in the regulation of pain. 4-39. The answer is a. (Murray, pp 15–26.) The equilibrium between an acid and its conjugate base is defined by the Henderson-Hasselbalch equation: [base] [acid] pH = pK a + log ᎏᎏ or [HCO3−] [CO2] pH = 6.1 + log ᎏᎏ in the case of carbonic acid. Note that CO2 is the effective acid and HCO3− the conjugate base for carbonic acid due to its complete dissociation in water. Given a pH of 7.1 in the cyanotic newborn, then 7.1 − 6.1 = 1 = log (10) = log [HCO3−]/[CO2] = log [HCO3−]/0.03 × PCO2. Since the [HCO3− ] is 12 mM, the PCO2 × 0.03 must be 1.2 mM and the PCO2 40 mmHg. This normal calculated value for PCO2 means that the baby must have metabolic acidosis, a common accompaniment of hypoxia (low PO2) that can be treated by providing oxygen or administering alkali to ameliorate the acidosis. If the baby had respiratory acidosis, the PCO2 would be elevated; this would be treated by increasing the respiratory rate to blow off CO2. Renal treatment of acidosis would require increasing acid excretion or alkali retention. The lungs compensate acidosis with increased breathing rates or tidal volumes to blow off CO2 and increase pH, the kidneys by retaining HCO3−. The lungs can compensate alkalosis somewhat by decreasing breathing rates or volumes to retain CO2 (and decrease oxygenation within limits), the kidneys by increasing excretion of HCO3−. 4-40. The answer is c. (Levinson, pp 302, 306, 307, 320–335.) All the diseases listed in the question have significant epidemiologic and clinical features. Toxoplasmosis, for example, is generally a mild, self-limiting disease; however, severe fetal disease is possible if pregnant women ingest Toxoplasma oocysts. Consumption of uncooked meat may result in either an acute toxoplasmosis or a chronic toxoplasmosis that is associated with serious eye disease. Most adults have antibody titers to Toxoplasma and thus would have a positive Sabin-Feldman dye test. Trichinosis most often is caused by ingestion of contaminated pork
  • Block 4 Answers 249 products. However, eating undercooked bear, walrus, raccoon, or possum meat also may cause this disease. Symptoms of trichinosis include muscle soreness and swollen eyes. Although giardiasis has been classically associated with travel in Russia, especially St. Petersburg (Leningrad), many cases of giardiasis caused by contaminated water have been reported in the United States as well. Diagnosis is made by detecting cysts in the stool. In some cases, diagnosis may be very difficult because of the relatively small number of cysts present. Alternatively, an enzyme immunoassay may be used to detect Giardia antigen in fecal samples. Schistosomiasis is a worldwide public health problem. Control of this disease entails the elimination of the intermediate host snail and removal of streamside vegetation. Abdominal pain is a symptom of schistosomiasis. Visceral larva migrans is an occupational disease of people who are in close contact with dogs and cats. The disease is caused by the nematodes Toxocara canis (dogs) and T. cati (cats) and has been recognized in young children who have close contact with pets or who eat dirt. Symptoms include skin rash, eosinophilia, and hepatosplenomegaly. 4-41. The answer is a. (McPhee, p 145. Braunwald, pp 175–179.) Sounds must be conducted through the middle ear and sensed by the cochlea and CN VIII; then they are processed by the cochlear nuclei and CNS pathways. Conductive deafness is hearing loss due to external auditory canal or middle ear disease. Sensineural deafness is a perceptive loss of hearing due to disease of the inner ear or eighth nerve. In conductive deafness, bone conduction is better than air conduction, and the reverse is the case for sensineural deafness. Central deafness is caused by disease affecting the central auditory pathways. Tinnitus an annoying noise in the ear that is usually benign, often is caused by cochlear or eighth nerve disorders. Hearing may be diminished, but the patient is not rendered fully deaf. Presbyacusis is hearing loss due to advanced age. 4-42. The answer is e. (Katzung, p 184. Hardman, p 764.) Nitric oxide is thought to be enzymatically released from nitroglycerin. It can then react with and activate guanylyl cyclase to increase GMP, a vasodilator due to its effect on increasing calcium efflux. It also indirectly causes the dephosphorylation of the light chains of myosin. These actions lead to the vasodilator effect of nitroglycerin. Reaction of nitric oxide occurs with
  • 250 Clinical Vignettes for the USMLE Step 1 protein sulfhydryl groups. Tolerance may develop in part from a decrease in available sulfhydryl groups. Autonomic receptors are not involved in the primary response of nitroglycerin, but compensatory mechanisms may counter the primary actions. 4-43. The answer is a. (Cotran, pp 15–18.) The cause of cell injury and death may sometimes be inferred from the type of necrosis present. Coagulative necrosis, characterized by loss of the cell nucleus, acidophilic change of the cytoplasm, and preservation of the outline of the cell, is seen in sudden, severe ischemia of many organs. It is not present, however, in acute ischemic necrosis of the brain. Myocardial infarction resulting from the sudden occlusion of the coronary artery is a classic example of coagulative necrosis. In contrast, with liquefactive necrosis the dead cells are completely dissolved by hydrolytic enzymes. This type of necrosis can be seen in ischemic necrosis of the brain, but classically it is associated with acute bacterial infections. Fat necrosis, seen with acute pancreatic necrosis, is fat cell death caused by lipases. Fibrinoid necrosis is an abnormality seen sometimes in injured blood vessels where plasma proteins abnormally accumulate within the vessel walls. Caseous necrosis is a combination of coagulative and liquefactive necrosis, but the necrotic cells are not totally dissolved and remain as amorphic, coarsely granular, eosinophilic debris. This type of necrosis grossly has the appearance of clumped cheese. It is classically seen in tuberculous infections. Gangrenous necrosis of extremities is also a combination of coagulative and liquefactive necrosis. In dry gangrene the coagulative pattern is predominate, while in wet gangrene the liquefactive pattern is predominate. 4-44. The answer is c. (Nolte, pp 418–423, 515–529.) The arterial occlusion involves both the temporal and occipital regions of cortex. Therefore, it would affect Wernicke’s area as well as primary visual areas of the occipital lobe. The patient would most likely present with receptive aphasia as well as a right homonymous hemianopsia. The lesion would not likely produce marked intellectual deficits since the prefrontal cortex was spared; nor would it produce hemiballism since there was no damage to the subthalamic nucleus. 4-45. The answer is b. (Kandel, pp 1305–1309. Nolte, pp 120–128.) Although the tissue affected involves parietal, temporal, and occipital
  • Block 4 Answers 251 lobes, the primary artery affected is the middle cerebral artery. The unusual feature of this occlusion is that it appears that the middle cerebral artery extends more caudally than usual. Nevertheless, the middle cerebral artery is the only one of the choices presented that could account for the damage to the temporal and parietal cortices. The anterior cerebral artery supplies the medial aspects of the frontal and parietal lobes; the posterior cerebral artery supplies the occipital cortex (visual areas); the posterior choroidal artery mainly supplies part of the tectum, the medial and superior aspects of the thalamus, and the choroid plexus of the third ventricle. The superior cerebellar artery supplies the dorsolateral aspect of a portion of the pons and the cerebellum. 4-46. The answer is e. (Braunwald, pp 459–461.) Empirical studies have revealed a number of changes in eating habits that will significantly discourage the tendency to eat more food than is required by the body. Nutritional experts recommend that we eat more slowly, serve ourselves smaller portions, wait at least 20 min after we have eaten our first serving before taking a second one, restrict all our eating to one or two places in the home, do not watch television or read while we are eating, and let family and friends know that we are trying to cut down on food intake. In addition, we should go grocery shopping only after we have eaten a satisfying meal, not leave food out where we repeatedly see it and can easily reach it many times a day, try to spend less time in the kitchen, get someone else in the family to clear the plates and put away the leftovers, and monitor eating habits by keeping a detailed log or diary of all food intake. Such activities will help to disrupt previously learned, but inappropriate, eating behaviors and establish appropriate environmental conditions and eating behaviors. 4-47. The answer is c. (Braunwald, pp 568, 1607.) The incidence of malignancy in duodenal ulcer is low, so a biopsy of the ulcer is not indicated. Surgery or other procedures are not necessary in uncomplicated ulcers. 4-48. The answer is c. (McPhee, pp 544–548. Braunwald, pp 2088, 2091–2092.) Androgen insensitivity can present as an inability for a male child to go into puberty. Low FSH and LH are expected to yield low testosterone levels. High FSH and LH are usually markers of end organ damage and lack of feedback of testosterone on the pituitary due to low levels.
  • 252 Clinical Vignettes for the USMLE Step 1 Puberty can be delayed by hypothyroidism, with FSH and LH usually appropriate to the testosterone level. XXY karyotype (Klinefelter’s) often has no effect on testosterone level. 4-49. The answer is a. (Cotran, pp 712–716.) Chronic obstructive pulmonary diseases (COPDs) are characterized by obstruction to airflow somewhere along the airways. These diseases may affect the bronchus, the bronchiole, or the acinus. Asthma, bronchiectasis, and chronic bronchitis affect primarily the bronchus, while emphysema affects primarily the acinus. Asthma is a pulmonary disease that is caused by excessive bronchoconstriction secondary to airways that are hyperreactive to numerous stimuli. Asthma has been divided into extrinsic and intrinsic categories. The extrinsic category includes atopic (allergic) asthma, occupational asthma, and allergic bronchopulmonary aspergillosis. The intrinsic category includes nonreaginic asthma and pharmacologic asthma. The former is related to respiratory tract infections, while the latter is often related to aspirin sensitivity. These aspirin-sensitive patients often have recurrent rhinitis and nasal polyps. In these patients the aspirin initiates an asthmatic attack by inhibiting the cyclooxygenase pathway of arachidonic acid metabolism without affecting the lipoxygenase pathway. This causes the relative excess production of the leukotrienes, which are bronchoconstrictors. 4-50. The answer is i. (Katzung, p 984.) Bacille Calmette-Guérin vaccine is a nonspecific stimulant of the reticuloendothelial system. It is an attenuated strain of Mycobacterium bovis that appears most effective in small, localized bladder tumors. This agent is approved for intravesicular use in bladder cancer. Adverse reactions are associated with the renal system, such as problems with urination, infection, and cystitis.
  • BLOCK 5 Answers 5-1. The answer is e. (Cotran, p 1025.) Scrotal enlargement may be caused by cysts, tumors, inflammatory processes, or abnormalities of the blood vessels. Transillumination is helpful in differentiating between cysts (which transilluminate) and tumors (which do not). Examples of the latter include germ cell tumors and the adenomatoid tumor, a benign form of mesothelioma that histologically is composed of glandlike or slitlike spaces. Recall that the processus vaginalis is an outpouching of the peritoneum that enters into the scrotum. When the testis reaches the scrotum, the proximal portion of the processus vaginalis obliterates, but the distal portion persists and does not fuse. This forms the tunica vaginalis of the testis. Examples of cysts that involve this tunica vaginalis include hydroceles, hematoceles, chyloceles, and spermatoceles. Hydroceles contain clear fluid and result from developmental abnormalities or inflammatory processes. Hematoceles result from hemorrhage into a hydrocele, while chyloceles result from the accumulation of lymph fluid within the tunica as a result of elephantiasis. Spermatoceles refer to cystic enlargements of the efferent ducts or the rete testis with numerous spermatocytes present. 5-2. The answer is c. (Afifi, pp 227–230. Nolte, pp 260–262, 290–294.) For a lesion to produce both an ipsilateral gaze paralysis and contralateral hemiplegia, it must be situated in a location where fibers regulating both lateral gaze and movements of the contralateral limbs lie close to each other. The only such location is the ventrocaudal aspect of the pons, where fibers of cranial nerve VI descend toward the ventral surface of the brainstem and where corticospinal fibers are descending toward the spinal cord. The other regions listed in the question do not meet this condition. 5-3. The answer is c. (Cotran, pp 106–110.) Tissue repair occurs through the regeneration of damaged cells and the replacement of tissue by connective tissue. Tissue repair involves the formation of granulation tissue, which histologically is characterized by a combination of prolifer253 Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  • 254 Clinical Vignettes for the USMLE Step 1 ating fibroblasts and proliferating blood vessels. Proliferating cells are cells that are rapidly dividing and usually have prominent nucleoli. This histologic feature should not be taken as a sign of dysplasia or malignancy. It is important not to confuse the term granulation tissue with the similarsounding term granuloma. The latter refers to a special type of inflammation that is characterized by the presence of activated macrophages (epithelioid cells). 5-4. The answer is e. (Braunwald, pp 1581.) The characteristics of acute pancreatitis include nausea and vomiting, abdominal pain, low-grade fever, and an elevated serum amylase. The pain is located primarily in the epigastrium and radiates into the back and usually is continuous and boring in quality. Fever may or may not be present. Serum amylase and lipase are usually elevated in the acute stages. 5-5. The answer is b. (Moore & Dalley, pp 621, 626.) The medial meniscus is attached to the medial collateral ligament. It is relatively immovable and, therefore, unable to evade damage such as occurred in this case. The medial meniscus is clearly not attached to the popliteus muscle or to the anterior cruciate ligament. 5-6. The answer is 5-6-a. (Levinson, pp 302, 306, 307, 320–335.) All the diseases listed in the question have significant epidemiologic and clinical features. Toxoplasmosis, for example, is generally a mild, self-limiting disease; however, severe fetal disease is possible if pregnant women ingest Toxoplasma oocysts. Consumption of uncooked meat may result in either an acute toxoplasmosis or a chronic toxoplasmosis that is associated with serious eye disease. Most adults have antibody titers to Toxoplasma and thus would have a positive Sabin-Feldman dye test. Trichinosis most often is caused by ingestion of contaminated pork products. However, eating undercooked bear, walrus, raccoon, or possum meat also may cause this disease. Symptoms of trichinosis include muscle soreness and swollen eyes. Although giardiasis has been classically associated with travel in Russia, especially St. Petersburg (Leningrad), many cases of giardiasis caused by contaminated water have been reported in the United States as well. Diagnosis is made by detecting cysts in the stool. In some cases,
  • Block 5 Answers 255 diagnosis may be very difficult because of the relatively small number of cysts present. Alternatively, an enzyme immunoassay may be used to detect Giardia antigen in fecal samples. Schistosomiasis is a worldwide public health problem. Control of this disease entails the elimination of the intermediate host snail and removal of streamside vegetation. Abdominal pain is a symptom of schistosomiasis. Visceral larva migrans is an occupational disease of people who are in close contact with dogs and cats. The disease is caused by the nematodes Toxocara canis (dogs) and T. cati (cats) and has been recognized in young children who have close contact with pets or who eat dirt. Symptoms include skin rash, eosinophilia, and hepatosplenomegaly. 5-7. The answer is e. (Cotran, pp 473–475.) Hemolytic disease of the newborn (HDN) is a type of isoimmune hemolytic anemia that is caused by maternal antibodies that react against fetal red blood cells. Once the maternal antibodies cross the placenta, the fetal red cells are destroyed, leading to a hemolytic anemia. The breakdown of hemoglobin leads to hyperbilirubinemia (jaundice), which is due to severe unconjugated hyperbilirubinemia, as the released heme is not easily conjugated by the immature newborn liver, which is deficient in glucuronyl transferase. The unconjugated bilirubin is water-insoluble and has an affinity for lipids. In an infant with a poorly developed blood-brain barrier, the bilirubin may bind to the lipids in the brain and produce kernicterus. The severe anemia may result in congestive heart failure, which, together with hypoproteinemia may lead to generalized edema (anasarca), which in its most severe form is called hydrops fetalis. In the peripheral blood of the newborn, many immature red blood cells may be found (nucleated RBCs or normoblasts). This condition is called erythroblastosis and led to another name for HDN being erythroblastosis fetalis. In order for the mother to make antibodies that are directed against fetal erythrocyte antigens, she must lack the erythrocyte antigens that the child has, which were inherited from the father. The most important erythrocyte antigens involved in HDN are the Rh and the ABO antigens. The most important Rh antigen is the D antigen. Therefore, for Rh incompatibility, the mother must be Rh negative (d), the child Rh positive (D). For ABO incompatibility, the mother must be type O (lacking the A and B antigens), the child type A or B. ABO incompatibility is the most common
  • 256 Clinical Vignettes for the USMLE Step 1 cause of hemolytic disease of the newborn. Usually the disease is less severe than HDN due to Rh incompatibility because there is poor expression of blood group antigens A and B on neonatal red cells. 5-8. The answer is d. (Katzung, p 969.) Cyclosporine is a peptide antibiotic that both inhibits early stages of differentiation of T cells and blocks their activation. This most likely occurs in activated T lymphocytes by inhibition of gene transcription of immune-enhancing substances such as interferon γ and interleukins. Cyclophosphamide, an alkylating agent, destroys proliferating lymphoid cells. Sirolimus amarolide ab blocks the response of T cells to cytokines. Methotrexate is an inhibitor of folic acid synthesis. Azathioprine inhibits enzymes that are related to the biosynthesis of purines. 5-9. The answer is d. (Kandel, pp 978–980.) Vasopressin is produced mainly from the magnocellular neurons of the hypothalamus. The hormone is released into the capillaries of the posterior pituitary. When it is released into the vascular system, it stimulates the kidneys to conserve water. The action of oxytocin is related to functions of the uterus and breasts. This hormone plays a role in the expulsion of the fetus at birth and in the milk ejection reflex following suckling. Substance P, histamine, and somatostatin are not known to relate specifically to this process. 5-10. The answer is b. (Murray, pp 258–297. Scriver, pp 2705–2716. Sack, pp 121–138. Wilson, pp 362–367.) Mevastatin, an analogue of mevalonic acid, acts as a feedback inhibitor of 3′-hydroxy-3′-methylglutaryl CoA (HMG-CoA) reductase, the regulated enzyme of cholesterol synthesis. Effective treatment with mevastatin, along with a low-fat diet, decreases levels of blood cholesterol. The lowering of cholesterol also lowers the amounts of the lipoprotein that transports cholesterol to the peripheral tissues, lowdensity lipoprotein (LDL). Since lipids like cholesterol and triglycerides are insoluble in water, they must be associated with lipoproteins for transport and salvage between their major site of synthesis (liver) and the peripheral tissues. Those lipoproteins associated with more insoluble lipids thus have lower density during centrifugation, a technique that separates the lowestdensity chylomicrons from very-low-density lipoproteins (VLDLs with preβ lipoproteins), low-density lipoproteins (LDLs with β-lipoproteins), intermediate-density lipoproteins (IDLs), and high-density lipoproteins
  • Block 5 Answers 257 (HDLs with α-lipoproteins). Each type of lipoprotein has typical apolipoproteins such as the apo B100 and apo B48 (translated from the same messenger RNA) in LDL. LDL is involved in transporting cholesterol from the liver to peripheral tissues, while HDL is a scavenger of cholesterol. The ratio of HDL to LDL is thus a predictor of cholesterol deposition in blood vessels, the cause of myocardial infarctions (heart attacks). The higher the HDL/LDL ratio, the lower the rate of heart attacks. 5-11. The answer is b. (Braunwald, pp 28, 640–641.) Iron and folate deficiencies occur in pregnancy because the fetus uses these substances in large amounts. The pregnant woman needs adequate supplements of iron and folate. Autoantibodies and vitamin B12 are not unique causes of iron deficiency in pregnancy. The history precludes gastrointestinal bleeding and menses as causes of this patient’s blood loss. 5-12. The answer is c. (Hardman, p 1086.) Ticarcillin resembles carbenicillin and has a high degree of potency against Pseudomonas and Proteus organisms but is broken down by penicillinase produced by various bacteria, including most staphylococci. Oxacillin, cloxacillin, nafcillin, and dicloxacillin are all resistant to penicillinase and are effective against staphylococci. 5-13. The answer is c. (April, pp 261–262, 273. Moore & Dalley, p 99.) The patient has a left pneumothorax. The lucidity of the left pleural cavity with the lack of pulmonary vessels indicates that the left lung has collapsed into a small, dense mass adjacent to the mediastinum. Such a nontraumatic pneumothorax may result from the rupture of a pulmonary bleb, especially in a young person. The right lung is normal. There is no pleural fluid level indicative of hemothorax, and the near symmetry of the domes of the two hemidiaphragms on inspiration indicates normal function of the phrenic nerves. The pleural cavities normally extend superior to the first rib into the base of the neck. The heart, measuring less than one-half of the chest diameter, is of normal size. 5-14. The answer is b. (Sierles, pp 76–80. Wedding, pp 274–275.) Contingency management is the technical term often used for positive reinforcement or stepping. It involves the process of changing the frequency of a behavior by controlling the consequences of that behavior with positive reinforcement to encourage or discourage a particular behavior. The proce-
  • 258 Clinical Vignettes for the USMLE Step 1 dure is used daily in our family and professional lives, such as rewarding (or punishing) children for their behavior and receiving (or being denied) a raise at work. Thus, a particular behavior becomes associated with a certain positive or negative consequence and the individual eventually accepts the desired behavior as being preferable. Behavior therapists have developed a wide range of applications for this learning procedure. A successful example is the token economy program (receiving tokens redeemable for snacks, movies, special privileges, and the like) which rewards destructive individuals for exhibiting appropriate behavior such as participating in rehabilitation activities. Contingency management has been effective with chronically hospitalized schizophrenic patients, such as the patient in the question who was disrupting the ward by shouting in the hall. Often, well-timed praise or friendliness will serve as an appropriate reinforcer to foster patient compliance, as will a lollipop for a child, or a follow-up phone call to a patient who has recovered or stopped smoking to reinforce your interest in their wellness, as well as their illness. In stimulus control, the attempt is to eliminate the stimulus or cue that triggers undesired behavior. Modeling exposes the individual to desirable behavior or stimuli (e.g., posters or advertisements showing high status persons resisting smoking or explaining how to resist peer pressure). 5-15. The answer is b. (Kandel, pp 910–918. Simon, pp 47, 258.) This person displays a complex partial seizure, which is characterized by a confusional state with brief losses of consciousness. It is called a partial seizure because the seizure involves a localized region, reflected by jerks of the muscles of a specific part of the body. The focus of this seizure is typically in the temporal lobe, such as the amygdala, hippocampal formation, or adjoining cortical regions. A simple partial seizure does not involve loss of consciousness. Absence seizures are nonconvulsive seizures and are also called petit mal seizures. Generalized seizures typically involve all of the limbs. The patient falls to the ground and loses consciousness. 5-16. The answer is c. (Howard, pp 285–286.) Except during a meningococcal epidemic, H. influenzae is the most common cause of bacterial meningitis in children. The organism is occasionally found to be associated with respiratory tract infections or otitis media. H. influenzae, N. meningitidis, S. pneumoniae, and Listeria account for 80 to 90% of all cases of bacterial meningitis. A purified polysaccharide vaccine conjugated to protein
  • Block 5 Answers 259 for H. influenzae type B is available. A tetravalent vaccine is available for N. meningitidis and a 23-serotype vaccine for S. pneumoniae. No vaccine is available for Listeria. 5-17. The answer is d. (Cotran, pp 1281–1283.) Duchenne’s muscular dystrophy (DMD) is a noninflammatory inherited myopathy that causes progressive, severe weakness and degeneration of muscles, particularly the proximal muscles, such as the pelvic and shoulder girdles. The defective gene is located on the X chromosome and codes for dystrophin, a protein found on the inner surface of the sarcolemma. Histologically, muscle fibers in patients with DMD show variations in size and shape, degenerative and regenerative changes in adjacent myocytes, necrotic fibers invaded by histiocytes, and progressive fibrosis. There are rounded, atrophic muscle fibers mixed with hypertrophied fibers. These muscle changes cause creatine kinase levels in the serum to be elevated. The weak muscles are replaced by fibrofatty tissue, which results in pseudohypertrophy. In Duchenne’s muscular dystrophy, symptoms begin before the age of 4, are progressive and lead to difficulty in walking, and are eventually followed by involvement of respiratory muscles, which causes death from respiratory failure before the age of 20. The classification of the muscular dystrophies is based on the mode of inheritance and clinical features. X-linked inheritance characterizes Duchenne’s muscular dystrophy, autosomal dominant inheritance characterizes both myotonic dystrophy and the fascioscapulohumeral type, and limb-girdle dystrophy is autosomal recessive. Sustained muscle contractions and rigidity (myotonia) are seen in myotonic dystrophy, the most common form of adult muscular dystrophy. In contrast, dermatomyositis is an autoimmune disease that is one of a group of idiopathic inflammatory myopathies. The inflammatory myopathies are characterized by immune-mediated inflammation and injury of skeletal muscle and include polymyositis, dermatomyositis, and inclusion-body myositis. These diseases are associated with numerous types of autoantibodies, one of which is the anti-Jo-1 antibody. The capillaries are the principle target in patients with dermatomyositis. Damage is by complement-mediated cytotoxic antibodies against the microvasculature of skeletal muscle. In addition to proximal muscle weakness, patients typically develop a lilac discoloration around the eyelids with edema. Patients may also develop erythema over their knuckles (Gorton’s sign). Histologically, examination of muscles from patients with dermatomyositis reveals perivascular inflammation within
  • 260 Clinical Vignettes for the USMLE Step 1 the tissue around muscle fascicles. This is in contrast to the other types of inflammatory myopathies, where the inflammation is within the muscle fascicles (endomysial inflammation). In particular, inclusion-body myositis is characterized by basophilic granular inclusions around vacuoles (“rimmed” vacuoles). Werdnig-Hoffmann disease is a severe lower motor neuron disease that presents in the neonatal period with marked proximal muscle weakness (“floppy infant”). 5-18. The answer is d. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp 57–76. Wilson, pp 227–246.) This child has several minor anomalies, a major anomaly that affects the genitalia, and developmental delay. These multiply affected and embryologically unrelated body regions suggest a syndrome rather than a sequence. Because of the multiple anomalies and developmental delay, the first diagnostic test to be considered is a karyotype rather than a test for specific organ function, such as serum testosterone. 5-19. The answer is a. (Braunwald, pp 1741.) Patients with achalasia present with a history of dysphagia or sensation of food sticking, which includes both liquids and solids. They have a long history of these symptoms and might come for treatment at an older age. 5-20. The answer is b. (Hardman, pp 1268–1269.) Asparaginase is an enzyme that catalyzes the hydrolysis of serum asparagine to aspartic acid and ammonia. Major toxicities are related to antigenicity and pancreatitis. In addition, more than 50% of those treated present biochemical evidence of hepatic dysfunction. 5-21. The answer is a. (Braunwald, pp 244–245.) Many physicians are concerned that there is an epidemic of obesity in the United States. One contributing factor is the increased availability of attractive, tasty, high-fat, high-calorie, and low-cost foods. A person does not become fat without overeating. Furthermore, many physicians have observed that obese patients have elevated, rather than depressed, absolute resting metabolic rates. Obesity is rarely caused by pathologic mechanisms or by disease. However, obesity does predispose an individual to disease, especially diabetes mellitus. Obese patients are also predisposed to gallstones, degenerative joint disease, hyperlipidemia, atherosclerosis, hypertension, sleep apnea, and some forms of cancer.
  • Block 5 Answers 261 5-22. The answer is c. (Braunwald, pp 1590–1591.) Patients with hypertensive (hypercontracting) LES experience less dysphagia than patients with esophageal spasm, and they do not complain of food sticking as do patients with achalasia. The pain associated with hypertensive LES does not have the characteristic of cardiac origin. 5-23. The answer is a. (Murray, pp 575–587. Scriver, pp 4077–5016. Sack, pp 121–144. Wilson, pp 287–324.) Sex steroids are synthesized from cholesterol by side chain cleavage (employing a P450 enzyme) to produce pregnenolone. Pregnenolone is then converted to testosterone in the testis, to estrogen in the ovary, and to corticosterone and aldosterone in the adrenal gland. The enzymes 3β-hydroxysteroid dehydrogenase, 21-hydroxylase, 11β-hydroxylase, and 18-hydroxylase modify pregnenolone to produce other sex and adrenal steroids. Deficiencies in adrenal 21-hydoxylase can thus lead to inadequate testosterone production in males and produce ambiguous external genitalia. Such children can also exhibit low sodium and high potassium due to deficiency of the more distal steroids, cortisol and aldosterone. 5α-reductase converts testosterone to dihydrotestosterone, and its deficiency produces milder degrees of hypogenitalism without salt wasting. Deficiency of the androgen receptor is called testicular feminization, producing normal-looking females who may not seek medical attention until they present with infertility. 5-24 and 5-25. The answers are 5-24 d, 5-25 a. (Adams, p 280, 538. Afifi, pp 163–168, 179–184, 209–220, 227–229. Kandel, pp 962–974.) Herb’s drooping eyelid, small pupil, and lack of sweating on the right side are examples of Horner’s syndrome. This is caused by the interruption of sympathetic fibers anywhere along their course from the hypothalamus and brainstem, to the intermediolateral cell column in the upper thoracic levels of the spinal cord where neurons, supplying sympathetic innervation to the pupil, the levator palpebrae superioris muscle of the eyelid and sweat glands of the face, are located. Interruption of this sympathetic innervation will result in the drooping of the upper eyelid (ptosis), pupillary constriction (miosis; due to unopposed action of the parasympathetic innervation of the circular muscles of the iris), and lack of sweating on the face. Parasympathetic or oculomotor damage causes pupillary dilation, rather than constriction. Herb could close his eyes tightly because this function is mediated by the seventh nerve, which is not damaged by this lesion. Preganglionic sympathetic neurons are pre-
  • 262 Clinical Vignettes for the USMLE Step 1 dominantly cholinergic, and postganglionic sympathetic neurons are predominantly noradrenergic. Horner’s syndrome may be caused by either a preganglionic or postganglionic lesion. The location may be determined by the use of eyedrops specifically targeted at a particular neurotransmitter. One cause of interruption of the sympathetic fibers is a tumor of the apex (top portion) of the lung, called a Pancoast tumor. Because the apex of the lung is in close proximity to the spine, a Pancoast tumor may compress the upper thoracic spinal cord where the sympathetic fibers exit from it. Compression of the adjacent spinal nerves between C8 and T2, entering the brachial plexus, also interrupts the nerve supply to the hand and triceps muscle, causing numbness and weakness in these areas. Pancoast tumors do not often cause respiratory symptoms early on in their course because they are located far from the mainstem bronchi. Because these tumors have this unique location, the neurological abnormalities often predate the respiratory problems. The neurologist suspected that Herb may have a Pancoast tumor in the lung because of his long history of smoking. 5-26. The answer is d. (Baum, pp 139–140.) The health risk to individuals who are in bereavement from the loss of a loved one is often ignored. Prospective studies have shown that the stressful effects of severe life crises are a real risk factor to general health and to the immune system. A large cohort of middle-aged widowers demonstrated a 40% increase in their mortality rate in the first six months of bereavement following the death of their spouse. Furthermore, over one-half of the deaths were from cardiovascular causes. Other factors that may contribute to the increased mortality rate include sudden changes in lifestyle or environment and feelings of isolation or lack of support. 5-27. The answer is 5-27-d. (Levinson, pp 302, 306, 307, 320–335.) All the diseases listed in the question have significant epidemiologic and clinical features. Toxoplasmosis, for example, is generally a mild, self-limiting disease; however, severe fetal disease is possible if pregnant women ingest Toxoplasma oocysts. Consumption of uncooked meat may result in either an acute toxoplasmosis or a chronic toxoplasmosis that is associated with serious eye disease. Most adults have antibody titers to Toxoplasma and thus would have a positive Sabin-Feldman dye test. Trichinosis most often is caused by ingestion of contaminated pork products. However, eating undercooked bear, walrus, raccoon, or possum
  • Block 5 Answers 263 meat also may cause this disease. Symptoms of trichinosis include muscle soreness and swollen eyes. Although giardiasis has been classically associated with travel in Russia, especially St. Petersburg (Leningrad), many cases of giardiasis caused by contaminated water have been reported in the United States as well. Diagnosis is made by detecting cysts in the stool. In some cases, diagnosis may be very difficult because of the relatively small number of cysts present. Alternatively, an enzyme immunoassay may be used to detect Giardia antigen in fecal samples. Schistosomiasis is a worldwide public health problem. Control of this disease entails the elimination of the intermediate host snail and removal of streamside vegetation. Abdominal pain is a symptom of schistosomiasis. Visceral larva migrans is an occupational disease of people who are in close contact with dogs and cats. The disease is caused by the nematodes Toxocara canis (dogs) and T. cati (cats) and has been recognized in young children who have close contact with pets or who eat dirt. Symptoms include skin rash, eosinophilia, and hepatosplenomegaly. 5-28. The answer is a. (Murray, pp 468–487. Scriver, pp 3–45. Sack, pp 245–257. Wilson, pp 151–180.) Imbalance of globin chain synthesis occurs in the thalassemias. Deficiency of α-globin chains (α thalassemia) is common in Asian populations and may be associated with abnormal hemoglobins composed of four β-globin chains (hemoglobin H) or (in fetuses and newborns) of four γ-globin chains (hemoglobin Bart’s). Mutation in a transcription factor necessary for expression of α-globin could ablate α-globin expression, since the same factor could act in trans on all four copies of the α-globin genes (two α-globin loci). Mutation of a regulatory sequence element that acts in cis would inactivate only one α-globin gene, leaving others to produce α-globin in reduced amounts (mild α thalassemia). Deletions of one α-globin would produce a similar mild phenotype, and deficiencies of transcription factors regulating α- and β-globin genes would not produce chain imbalance. 5-29. The answer is c. (Damjanov, pp 1006–1008. Cotran, p 247, 381–382.) Infection by the protozoan P carinii is characterized by the pres. ence of oval and helmet-shaped organisms whose capsules are made more visible by use of Gomori’s methenamine-silver staining technique. This organism, although it has low virulence, is opportunistic; it is often seen to
  • 264 Clinical Vignettes for the USMLE Step 1 attack severely ill, immunologically depressed patients. It is frequently the first opportunistic infection to be diagnosed in HIV-1–positive patients, and it is a leading cause of death in patients with AIDS. 5-30. The answer is d. (Levinson, pp 51–52, 68, 70, 141–142.) This question demonstrates commonly occurring clinical infectious diseases and microbiologic problems. Enterococci may be resistant to ampicillin and gentamicin. Vancomycin would be the drug of choice. However, laboratory results do not always correlate well with clinical response. The National Committee on Clinical Laboratory Standards recommends testing enterococci only for ampicillin and vancomycin. Some symptomatic patients may have 10 leukocytes per mL of urine but relatively few bacteria. The patient is likely infected and the organisms, particularly if in pure culture, should be further processed. 5-31. The answer is e. (Katzung, pp 340–342.) Salmeterol is a longacting β2-adrenergic agonist that is effective in asthma prophylaxis. Skeletal muscle tremor is associated with β2-adrenergic agonists, whether short acting or not. Other shorter-acting β2-adrenergic agonists include albuterol and terbutaline. 5-32. The answer is c. (Cotran, pp 984–985.) A rare cause of hypertension is renal artery stenosis, which may occur secondary to either an atheromatous plaque at the orifice of the renal artery or fibromuscular dysplasia of the renal artery. The former is more common in elderly men, while the latter is more common in young women. The decrease in blood flow to the kidney with the renal artery obstruction (Goldblatt’s kidney) causes hyperplasia of the juxtaglomerular apparatus and increased renin production. This produces increased secretion of angiotensin and aldosterone, which leads to retention of sodium and water and produces hypertension. Increased levels of aldosterone also produce a hyperkalemic alkalosis. The kidney with stenosis of the renal artery becomes small and shrunken due to the effects of chronic ischemia, but the stenosis protects this kidney from the effects of the increased blood pressure. The other kidney, however, is not protected and may develop microscopic changes of benign nephrosclerosis (hyaline arteriolosclerosis). 5-33 and 5-34. The answers are 5-33 c, 5-34 a. (Purves, p 130. Siegel, pp 328–332.) It has been discovered that one mechanism of neuro-
  • Block 5 Answers 265 degeneration involves prolonged activation of neurons by glutamate. It is believed that if glutamate accumulates in the extracellular space and is not removed, the presence of glutamate will effectively stimulate the neuron to death. It has been shown that neurotoxicity is linked to cell death after a stroke, which causes brain ischemia and oxygen deprivation. Glutamate receptors are involved in ischemic cell damage in the following way: Glutamate released from the presynaptic terminal would normally activate NMDA and AMPA receptors in the postsynaptic membrane. This results in an increase in the intracellular concentration of Ca2+, which remains long after the initial stimulus is removed, and thus prevents the cell from reestablishing a resting membrane potential. The net effect here is to produce injury (or death) to the cell. 5-35. The answer is c. (McPhee, pp 531–539. Braunwald, pp 2106–2108.) One of the least recognized causes of infertility in a female is scarring of the uterus postpartum, called Asherman’s syndrome. It classically follows curettage of the uterus, such as occurred here. Women with this syndrome are infertile because an inability to implant. Ovarian failure, hypothyroidism, and prolactinoma are all eliminated because she still has scant regular menses. Endometriosis causes painful menses. 5-36. The answer is b. (Murray, pp 468–487. Scriver, pp 4517–4554. Sack, pp 245–257. Wilson, pp 151–180.) Red cell hemolysis after drug exposure suggests a red cell enzyme defect, most easily confirmed by enzyme assay to demonstrate deficient activity. A likely diagnosis here is glucose-6phosphate dehydrogenase (G6PD) deficiency (305900), probably the most common genetic disease (it affects 400 million people worldwide). Tropical African and Mediterranean peoples exhibit the highest prevalence because the disease, like sickle cell trait, confers resistance to malaria. DNA analysis is available to demonstrate particular alleles, but simple enzyme assay is sufficient for diagnosis. More than 400 types of abnormal G6PD alleles have been described, meaning that most affected individuals are compound heterozygotes. The phenotype of jaundice and red blood cell hemolysis with anemia is triggered by a variety of infections and drugs, including a dietary substance in fava beans. Sulfonamide and related antibiotics as well as antimalarial drugs are notorious for inducing hemolysis in G6PD-deficient individuals. G6PD deficiency exhibits X-linked recessive inheritance, explaining why male offspring but not the parents become ill when exposed to antimalarials.
  • 266 Clinical Vignettes for the USMLE Step 1 5-37. The answer is d. (Hardman, p 1346.) A slow intravenous infusion of protamine sulfate will quickly reverse the bleeding. Protamine binds to heparin to form a stable complex with no anticoagulant activity. It may also have its own anticoagulant effect by binding with platelets and fibrinogen. 5-38. The answer is b. (Moore & Dalley, pp 843–845.) The arrow points to the sella turcica, which cradles the pituitary gland. The stalk of the gland can be seen directly above the sella turcica. Surgically, the nasal approach to the pituitary is through the nasal cavity, sphenoidal sinus, and the inferior wall of the sella turcica. The other midline structures are the pharyngeal tonsil (which lies inferior to this region), and portions of the circle of Willis and the basilar artery, which both lie within the cranial cavity. 5-39. The answer is c. (Kaplan, pp 151–152.) Systematic desensitization was developed by Joseph Wolpe in an effort to decrease neurotic anxiety or phobias that are learned and are usually precipitated by certain environmental situations, such as fear of heights or crowds. The patient is taught muscular relaxation; then, while using the relaxation to inhibit the anxiety, the patient is told to imagine a series of progressively more severe anxietyprovoking situations (e.g., climbing to the second step of a ladder, then the fourth step, and so on) until the anxiety-provoking situation of the highest (strongest) level can be brought to mind without the accompanying anxiety or fear. The anxiety-provoking situation is not brought to mind to be treated by any special form of psychotherapy but becomes paired with the anxiety-reducing relaxation. Most of these anxiety-provoking situations are situation-specific; however, the desensitization often generalizes to other real-life situations that may be potentially anxiety-provoking. 5-40. The answer is e. (Cotran, pp 160–163. Rubin, pp 255–257.) The glycogen storage diseases are due to defective metabolism of glycogen, and at least 11 syndromes stemming from genetic defects in the responsible enzymes have been described. Most of these glycogenoses are inherited as autosomal recessive disorders. von Gierke’s disease (type I) results from deficiency of glucose-6-phosphatase, the hepatic enzyme needed for conversion of G6P to glucose, with glycogen accumulation particularly in the enlarged liver and kidney and hypoglycemia. Diagnosis requires biopsy demonstration of excess liver glycogen plus either absent or low liver glucose-6-phosphatase activity, or a diabetic glucose tolerance curve, or hyperuricemia. von Gierke’s disease is the major hepatic or hepatorenal
  • Block 5 Answers 267 type of glycogenosis. Lysosomal glucosidase deficiency causes Pompe’s disease (type II). Glycogen storage is widespread but most prominent in the heart (cardiomegaly). In brancher glycogenosis (type IV) there is accumulation of amylopectin or abnormal glycogen in the liver, heart, skeletal muscle, and brain. The major myopathic form, McArdle’s disease (type V), is due to lack of muscle phosphorylase. 5-41. The answer is a. (Siegel, pp 319–321.) NMDA ion channels are opened by both glutamate and glycine. On the other hand, Mg2 generates a voltage-dependent block of this ion channel. The drug of abuse, phencyclidine (PCP), also utilizes a similar mechanism to block NMDA-receptor channels. The other choices do not relate to this mechanism with respect to PCP. 5-42. The answer is a. (Sierles, pp 182–184. Wedding, pp 184–199.) There are a number of ways a physician can facilitate an interview, but in this case momentary silence would be most appropriate; i.e., you should continue to listen and perhaps offer a tissue, a nod, or a simple affirmation of understanding her import, such as “I see.” This would do more to support her by letting her express her feelings and not interrupt her flow of thoughts with another question or statement. Studies show that doctors tend to interrupt a patient after about 18 seconds and that crying is very upsetting to many doctors, who then feel compelled to say something—anything. Statements such as “I know how you feel” are usually inappropriate because most doctors do not know how a patient feels (unless they have had a son come home with AIDS). “Don’t worry, it’ll be OK” is a shallow response and does not support or help the patient, as the patient realizes that the doctor does not know that the patient will be fine. The question “Why are you so upset” is often interpreted as an accusation or inability to understand or express empathy. Saying “You know you can tell me anything” may be an attempt to reassure the patient, but it is inappropriate in a new patient who does not know that you can be told everything at this point in the relationship. The question “Are you thinking you may have AIDS?” is an inappropriate interruption and a very unlikely guess as to what may be upsetting the patient. It could be appropriate later in the interview, but only after exploring many other physical and psychological factors. 5-43. The answer is b. (McPhee, p 296.) The goal for improving the symptoms of GERD is to increase or maintain the LES pressure. High-
  • 268 Clinical Vignettes for the USMLE Step 1 protein meals generally increase LES pressure and should be encouraged. Fats, chocolate, and alcohol decrease LES pressure and these foods should be avoided. Carbohydrate content does not affect motility. 5-44. The answer is b. (April, p 265.) A Pancoast tumor in the apex of the right lung may compress the right brachiocephalic vein with resultant venous engorgement of the right arm and right side of the face and neck. In addition, there may be compression of the brachial artery, the sympathetic chain, and recurrent laryngeal nerve with attendant deficits. An aneurysm of the aortic arch could reduce pulse pressures as the great vessels are occluded, but it could not explain the venous congestion. 5-45. The answer is 487-d. (McPhee, p 145. Braunwald, pp 175–179.) Sounds must be conducted through the middle ear and sensed by the cochlea and CN VIII; then they are processed by the cochlear nuclei and CNS pathways. Conductive deafness is hearing loss due to external auditory canal or middle ear disease. Sensineural deafness is a perceptive loss of hearing due to disease of the inner ear or eighth nerve. In conductive deafness, bone conduction is better than air conduction, and the reverse is the case for sensineural deafness. Central deafness is caused by disease affecting the central auditory pathways. Tinnitus an annoying noise in the ear that is usually benign, often is caused by cochlear or eighth nerve disorders. Hearing may be diminished, but the patient is not rendered fully deaf. Presbyacusis is hearing loss due to advanced age. 5-46. The answer is c. (Conger, pp 55–68.) The growth spurt takes approximately 41⁄2 years for both boys and girls but it normally occurs at about age 13 for boys and at about age 11 for girls. The range is between three to four years on either side of the average, making the variability of growth in adolescence considerable. At age 13, Tom is probably just beginning his growth spurt, while Jill, although the same age, is a year or two ahead of him developmentally and has already begun or reached her menarche. This is a critical time socially and emotionally for both. Tom’s growth spurt may have just begun while other boys in the school may be much farther ahead, resulting in feelings of inferiority and poor selfconcept for not meeting some fantasized ideal. Jill, on the other hand, has begun to menstruate and, like Tom, is experiencing radical changes, lowered self-concept, and even depression for fear of not “measuring up” to
  • Block 5 Answers 269 fantasized and media-portrayed ideals. It may be important to note that menarche occurs about nine months earlier in girls from families with higher incomes than from families with lower incomes. 5-47. The answer is b. (Levinson, pp 287–288.) Hairs infected with Microsporum canis and M. audouini both fluoresce with a yellow-green color under Wood’s light, while Trichophyton rubrum, T. tonsurans, and Epidermophyton floccosum do not. But M. audouini is an anthropophilic agent of tinea capitis, whereas M. canis is zoophilic. M. canis is primarily seen in children and is associated with infected cats or dogs. 5-48. The answer is d. (Cotran, pp 742, 744, 747.) Horner’s syndrome occurs with apical (superior sulcus) tumors of any type (Pancoast tumor), but since most peripheral cancers of the lung are adenocarcinomas, most tumors of the apex of the lung are adenocarcinomas. Horner’s syndrome is characterized by enophthalmos, ptosis, miosis, and anhidrosis on the same side as the lesion due to invasion of the cervical sympathetic nerves. Involvement of the brachial plexus causes pain and paralysis in the ulnar nerve distribution. 5-49. The answer is a. (Cotran, pp 1304–1305. Damjanov, pp 2733– 2736.) Epidural hemorrhages result from hemorrhages into the potential space between the dura and the bone of the skull. These hemorrhages result from severe trauma that typically causes a skull fracture. The hemorrhage results from rupture of one of the meningeal arteries, as these arteries supply the dura and run between the dura and the skull. The artery involved is usually the middle meningeal artery, which is a branch of the maxillary artery, as the skull fracture is usually in the temporal area. Since the bleeding is of arterial origin (high pressure), it is rapid and the symptoms are rapid in onset, although the patient may be normal for several hours (lucid interval). Bleeding causes increased intracranial pressure and can lead to tentorial herniation and death. 5-50. The answer is a. (Guyton, pp 189–190, 254–255.) The fall in blood volume and pressure produced by hemorrhage elicits the baroreceptor reflex. The reflex increases the activity of the sympathetic nervous system and decreases the activity of the parasympathetic nerves innervating the heart. Sympathetic stimulation of the smooth muscle surrounding the
  • 270 Clinical Vignettes for the USMLE Step 1 venous vessels decreases their compliance, causing end-diastolic volume (EDV) to increase. However, the EDV does not increase above the levels observed prior to the hemorrhage. Heart rate, ventricular contractility, and total peripheral resistance are all increased above their prehemorrhage levels by sympathetic stimulation. The coronary blood flow increases to meet the increased energy requirements of the heart beating at a higher rate with increased contractility.
  • BLOCK 6 Answers 6-1. The answer is d. (Simon, pp 164–168. Gilroy, pp 592–594.) In this case, disruption of the root fibers of C5–C6 involve components of the brachial plexus and affect muscle groups such as the deltoid, supraspinatus, intraspinatus, biceps, and flexor carpi radialis. These muscles govern abduction of the arm, rotation of the arm at the shoulder, flexion of the elbow and wrist. Reflex activity would also be affected due to disturbance of both alpha and gamma motor neurons serving the biceps muscle. Lesions involving the cerebral cortex or pons, especially the region of the pyramidal tracts, would produce a UMN paralysis, which would include hyperreflexia and hypertonia. An LMN paralysis involving the ventral horn cells at C1 would not affect the brachial plexus and the muscle groups indicated in this question. The triceps muscle is not involved in producing the movements affected by the injury. 6-2. The answer is e. (Waxman, pp 132, 150.) An MRI (magnetic resonance imaging) revealed a hemorrhage in the right subthalamic nucleus that is interconnected with the basal ganglia. The basal ganglia participate in feedback regulation of the motor system. The basal ganglia receive information from all regions of the cortex and project back to premotor and association cortex of the frontal lobe via the ventrolateral and ventroanterior thalamic nuclei. A direct pathway facilitates or excites cortical motor activity, whereas an indirect pathway inhibits cortical motor activity. Damage to the subthalamic nucleus decreases the inhibition of excitatory relay neurons in the thalamus, thus increasing the activation of cortical motor neurons, resulting in a characteristic form of jerky movement called ballism. Damage to an appropriate region of the cerebellum would result in loss of fine motor control but not in ballism. Damage to the neurons in the ventral horn of a specific level of the spinal cord would result in a localized flaccid paralysis. The hypothalamus is involved in vegetative functions, not voluntary movement. Damage to a localized portion of primary sensory cortex could not be expected to 271 Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  • 272 Clinical Vignettes for the USMLE Step 1 result in feedback deficits over both upper and lower extremities without other neurologic deficits. 6-3. The answer is e. (McPhee, p 240. Braunwald, p 1614.) The clinical findings in this patient are consistent with a diagnosis of Zollinger-Ellison syndrome (multiple peptic ulcers due to a gastrin-secreting tumor). Diarrhea accompanies the symptoms of peptic ulcer frequently. The patient is a young adult and lacks other symptoms of a gastric adenocarcinoma. Carcinoid causes diarrhea, but not often does it cause the ulcerative symptoms this patient exhibits. Also, this patient’s symptoms are inconsistent with lung or prostate carcinoma. 6-4. The answer is d. (Murray, pp 15–26.) Tachypnea in term infants may result from brain injuries or metabolic diseases that irritate the respiratory center. The increased respiratory rate removes (“blows off”) carbon dioxide from the lung alveoli and lowers blood CO2, forcing a shift in the indicated equilibrium toward the left: CO2 + H2O H2CO2 H+ + HCO3− Carbonic acid (H2CO2) can be ignored because negligible amounts are present at physiologic pH, leaving the equilibrium: CO2 + H2O H+ + HCO3− The leftward shift to replenish exhaled CO2 decreases the hydrogen ion (H+) concentration and increases the pH (-log10[H+]) to produce alkalosis (blood pH above the physiologic norm of 7.4). This respiratory alkalosis is best treated by diminishing the respiratory rate to elevate the blood [CO2], force the above equilibrium to the right, elevate the [H+], and decrease the pH. The newborn does not have acidosis, defined as a blood pH below 7.4, either from excess blood acids (metabolic acidosis) or from increased [CO2] (respiratory acidosis). The baby also does not have metabolic alkalosis, caused by loss of hydrogen ion from the kidney (e.g., with defective tubular filtration) or stomach (e.g., with severe vomiting). 6-5. The answer is e. (Cotran, pp 152–156. Rubin, pp 228–233.) Nondisjunction during the first meiotic division is responsible for trisomy 21 in about 93% of patients with Down’s syndrome. Nondisjunction during
  • Block 6 Answers 273 mitosis of a somatic cell early during embryogenesis results in mosaicism in about 2% of patients with Down’s syndrome. Translocation of an extra long arm of chromosome 21 causes about 5% of Down’s syndrome cases. An important type of translocation, the Robertsonian translocation (centric fusion), involves two nonhomologous acrocentric chromosomes with the resultant formation of one large metacentric chromosome. Carriers of this type of translocation may also produce children with Down’s syndrome. It is important to understand these different causes of Down’s syndrome in order to estimate the chance of recurrence if parents already have one child with Down’s syndrome. Overall, the risk of recurrence of trisomy 21 after one such child has been born to a family is about 1%. If the karyotypes of the parents are normal, then the recurrence rate is dependent upon the age of the mother. For mothers under the age of 30, the risk is about 1.4%. For mothers over the age of 30, the risk is the same as the agerelated maternal risk, which at age 30 is 1/900, at age 35 is 1/350, at age 40 is 1/100, and at age 40 and over is 1/25. The recurrence risk is different for a translocation Down’s syndrome, which may be either a 14q21q Robertsonian translocation or a 21q21q translocation. A carrier of a Robertsonian translocation involving chromosomes 14 and 21 has only 45 chromosomes and can theoretically produce six possible types of gametes. Of these, only three are potentially viable: one that is normal, one that is balanced, and one that is unbalanced, having both the translocated chromosome and a normal chromosome 21. The latter, when combined with a normal gamete, could produce a child with Down’s syndrome. Therefore, theoretically, the risk of a carrier of this type of Robertsonian translocation producing a child with Down’s syndrome would be 1 in 3. In practice, about 15% of the progeny of mothers with this type of translocation, and very few of the progeny of fathers with this type of translocation, develop Down’s syndrome. In contrast, carriers of a 21q21q translocation produce gametes that either have the translocated chromosome or lack any 21 chromosome. Progeny then can have either trisomy 21 or monosomy 21, but, since the latter is rarely viable, approximately 100% of progeny will have Down’s syndrome. 6-6. The answer is a. (Howard, pp 791–796.) Epstein-Barr virus (EBV) is a herpesvirus that causes a number of syndromes; the most common is infectious mononucleosis. It is a ubiquitous enveloped DNA virus. Only one serotype of EBV has been recognized, although molecular methods have reorganized a number of genotypes of EBV.
  • 274 Clinical Vignettes for the USMLE Step 1 Infectious mononucleosis is an acute disease most commonly seen in younger people. It is characterized by a proliferation of lymphocytes, lymph node enlargement, pharyngitis, fatigue, and fever. Infection in young children is usually either asymptomatic or characteristic of an acute upper respiratory infection. Diagnosis is usually made by a positive heterophil test. Heterophil antibodies are those that occur in one species (human) and react with antigens of a different species. The heterophil test may be insensitive (30 to 60%) in children. Definitive diagnosis is made by detection of antibodies to EBV components. EBV causes a variety of other syndromes including Burkitt’s lymphoma, the most common childhood cancer in Africa, and nasopharyngeal carcinoma, commonly seen in China. Similar mononucleosis-like diseases are caused by cytomegalovirus (CMV) and Toxoplasma gondii, a parasite. CMV causes fewer than 10% of infectious mononucleosis-like diseases. CMV “mono” is primarily characterized by fatigue. Congenital infection with CMV almost always causes serious sequelae, such as retardation and hearing loss. T. gondii also causes a variety of clinical problems, among them encephalitis in AIDS patients and food poisoning from the ingestion of raw meat. Although CMV and T. gondii are relatively rare causes of infectious mononucleosis, they must be ruled out, particularly when EBV tests are nonreactive. 6-7. The answer is e. (Nolte, pp 488–492.) Since the flocculonodular lobe receives and integrates inputs from the vestibular system, it is understandable why lesions that disrupt this integrating mechanism for vestibular inputs would result in difficulties in maintaining balance. Indeed, this is a classic feature of lesions of the flocculonodular lobe but is not associated with lesions in the hemispheres of the posterior lobe, anterior limb of the internal capsule, or the dentate nucleus, which are functionally linked to the frontal lobe. Lesions of the anterior lobe also do not affect mechanisms of balance. 6-8. The answer is e. (Hardman, p 1533.) Enthusiastic overmedication with vitamin D may lead to a toxic syndrome called hypervitaminosis D. The initial symptoms can include weakness, nausea, weight loss, anemia, and mild acidosis. As the excessive doses are continued, signs of nephrotoxicity are manifested, such as polyuria, polydipsia, azotemia, and eventually nephrocalcinosis. In adults, osteoporosis can occur. Also, there is CNS impairment, which can result in mental retardation and convulsions.
  • Block 6 Answers 275 6-9. The answer is b. (Braunwald, pp 253–255, 1664.) CT scan is very helpful in evaluating obstructive jaundice, particularly when a pancreatic source is suspected. For subtle lesions for which the differential diagnosis includes metastatic disease, vascular problems, or parenchymal disease, MRI is very helpful if the CAT scan is not diagnostic. An upper abdominal ultrasound is the ideal test to examine the gallbladder for stones, and a barium swallow is the initial study favored in the evaluation of patients with dysphagia. A KUB might show an enlarged liver, but contribute to the evaluation of jaundice, especially when the pancreas is involved. 6-10. The answer is b. (Levinson, pp 51–52, 68, 70, 141–142.) These questions demonstrate commonly occurring clinical infectious diseases and microbiologic problems. Enterococci may be resistant to ampicillin and gentamicin. Vancomycin would be the drug of choice. However, laboratory results do not always correlate well with clinical response. The National Committee on Clinical Laboratory Standards recommends testing enterococci only for ampicillin and vancomycin. Some symptomatic patients may have 10 leukocytes per mL of urine but relatively few bacteria. The patient is likely infected and the organisms, particularly if in pure culture, should be further processed. 6-11. The answer is e. (Murray, pp 375–401. Scriver, pp 2663–2704. Sack, pp 121–138. Wilson, pp 287–320.) Orotic aciduria is the buildup of orotic acid due to a deficiency in one or both of the enzymes that convert it to UMP. Either orotate phosphoribosyltransferase and orotidylate decarboxylase are both defective, or the decarboxylase alone is defective. UMP is the precursor of UTP, CTP, and TMP. All of these end products normally act in some way to feedback-inhibit the initial reactions of pyrimidine synthesis. Specifically, the lack of CTP inhibition allows aspartate transcarbamoylase to remain highly active and ultimately results in a buildup of orotic acid and the resultant orotic aciduria. The lack of CTP, TMP, and UTP leads to a decreased erythrocyte formation and megaloblastic anemia. Uridine treatment is effective because uridine can easily be converted to UMP by omnipresent tissue kinases, thus allowing UTP, CTP, and TMP to be synthesized and feedback-inhibit further orotic acid production. 6-12. The answer is a. (Cotran, pp 1314–1317.) Meningitis [inflammation of the arachnoid and the cerebrospinal fluid (CSF)], may be classified
  • 276 Clinical Vignettes for the USMLE Step 1 as acute pyogenic, aseptic, or chronic. The etiology and CSF findings vary in these three groups. The CSF in acute pyogenic meningitis, which is usually caused by bacteria, is grossly cloudy (not bloody, which is suggestive of a subarachnoid hemorrhage) and displays increased pressure, increased neutrophils, increased protein, and decreased glucose. With chronic meningitis, such as that caused by Mycobacterium tuberculosis, the CSF is clear grossly, with only a slight increase in leukocytes (either mononuclear cells or a mixed infiltrate), a markedly increased protein level, increased pressure, and moderately decreased or normal amounts of sugar. Both brain abscesses and subdural empyemas, which are parameningeal infections rather than direct meningeal infections, cause increased CSF pressure (more marked with abscess because of mass effect) along with increased inflammatory cells (lymphocytes and polys) and increased protein but a normal glucose level. The CSF is clear. Encephalitis, also not a direct infection of the meninges, results in clear CSF , increased pressure, increased protein, normal glucose, and possibly increased lymphocytes. 6-13. The answer is b. (April, p 57.) The horizontal direction of the fibers of the clavicular head of the pectoralis major muscle draws the humerus medially and causes the distal fragment of the bone to sublux. The sternal head of this muscle also has the effect of pulling the arm medially, an effect that is normally offset by the strutlike action of the clavicle. 6-14. The answer is d. (April, p 65.) Because large and important neurovascular structures pass between the clavicle and first rib, including the subclavian artery, clavicular fracture may produce life-threatening bleeding into the pleural cavity. The axillary artery is the continuation of the subclavian after it has cleared the first rib, so neither this vessel nor its thoracoacromial branch is likely to be threatened by clavicular fracture. There is no brachiocephalic artery on the left side, and on the right its terminal point is marked by its bifurcation into common carotid and subclavian arteries proximal to the fracture site. 6-15. The answer is c. (Levinson, pp 147–148.) The serologic diagnosis of Lyme disease is fraught with difficulty. Enzyme immunoassay (EIA) may be insensitive in the early stages of disease and may lack specificity in advanced stages. Western blot analysis of antibody is the confirmatory test for Lyme
  • Block 6 Answers 277 disease, but it, too, is not 100% sensitive and specific. The Western blot test detects antibodies to proteins and glycoproteins of Borrelia burgdorferi. Not all of these proteins are specific for the organism. For example, antibodies to Gp66 may reflect a cross-reaction, as many Gram-negative bacteria have similar glycoproteins. For this reason, a Western blot showing only antibodies to Gp66 is thought to be a nonspecific immune response. 6-16. The answer is b. (Cotran, pp 766–767. Rubin, pp 1331–1333.) Ménière’s disease is an abnormality that is characterized by periodic episodes of vertigo that are often accompanied by nausea and vomiting, sensorineural hearing loss, and tinnitus (ringing in the ears). These symptoms are related to hydropic dilation of the endolymphatic system of the cochlea. Inflammation of the middle ear (otitis media), which occurs most often in children, may be acute or chronic. If otitis media is caused by viruses, there may be a serous exudate, but if it is produced by bacteria, there may be a suppurative exudate. Acute suppurative otitis media is characterized by acute suppurative inflammation (neutrophils), while chronic otitis media involves chronic inflammation with granulation tissue. Chronic otitis media may cause perforation of the eardrum or may lead to the formation of a cyst within the middle ear that is filled with keratin, called a cholesteatoma. The name is somewhat of a misnomer, as cholesterol deposits are not present. Otosclerosis, a common hereditary cause of bilateral conduction hearing loss, is associated with formation of new spongy bone around the stapes and the oval window. Patients present with progressive deafness. Tumors of the middle ear are quite rare, but a neoplasm that arises from the paraganglia of the middle ear (the glomus jugulare or glomus tympanicum) is called a chemodectoma. Other names for this tumor include nonchromaffin paraganglioma and glomus jugulare tumor. This lesion is characterized histologically by lobules of cells in a highly vascular stroma (zellballen). A similar tumor that occurs in the neck is called a carotid body tumor. 6-17. The answer is d. (Hardman, p 1481.) Of the glucocorticoids listed, dexamethasone is the most potent. The dexamethasone suppression test has several uses—it allows not only complete suppression of pituitary ACTH production, but also accurate measurement of endogenous corticosteroids such as 17-ketosteroids in the urine. The small amount of dexamethasone present contributes minimally to this measurement.
  • 278 Clinical Vignettes for the USMLE Step 1 6-18. The answer is d. (Howard, p 457.) Helicobacter pylori was first recognized as a possible cause of gastritis and peptic ulcer by Marshall and Warren in 1984. This organism is readily isolated from gastric biopsies but not from stomach contents. It is similar to Campylobacter species and grows on chocolate agar at 37°C in the same microaerophilic environment suitable for C. jejuni (Campy-Pak or anaerobic jar [Gas Pak] without the catalyst). H. pylori, however, grows more slowly than C. jejuni, requiring 5 to 7 days incubation. C. jejuni grows optimally at 42°C, not 37°C, as does H. pylori. 6-19. The answer is e. (Cotran, pp 447–448. Chandrasoma, pp 160–162. Rubin, pp 348–349.) Vitamin B1 (thiamine) has three important functions. It participates in oxidative decarboxylation of α-keto acids; participates as a cofactor for transketolase in the pentose phosphate path; and participates in maintaining neural membranes. The causes of thiamine deficiency include poor diet, deficient absorption and storage, and accelerated destruction of thiamine diphosphate. This deficiency may be seen in alcoholics and prisoners of war because of poor nutrition, or it may be seen in individuals who eat large amounts of polished rice. (Polishing rice removes the outer, thiamine-containing portion of the grain.) Thiamine deficiency (called beriberi) mainly affects two organ systems, the heart and the nervous system. If the heart is affected in a patient with beriberi, it may become dilated and flabby. Patients may also develop peripheral vasodilation that leads to a high-output cardiac failure and marked peripheral edema. This combination of vascular abnormalities is called wet beriberi. The peripheral nerves in beriberi may be damaged by focal areas of myelin degeneration, which leads to footdrop, wristdrop, and sensory changes (numbness and tingling) in the feet and lower legs. These symptoms are referred to as dry beriberi. Thiamine deficiency may produce the central nervous system (CNS) symptoms of Wernicke-Korsakoff syndrome. Wernicke’s encephalopathy consists mainly of foci of hemorrhages and necrosis in the mammillary bodies and about the ventricular regions of the thalamus and hypothalamus, about the aqueduct in the midbrain, and in the floor of the fourth ventricle. Symptoms of Wernicke’s syndrome include progressive dementia (confusion), ataxia, and paralysis of the extraocular muscles—often with bilateral lateral rectus, or sixth nerve, palsies (ophthalmoplegia). Korsakoff psychosis is a thought disorder that produces retrograde memory failure and confabulation.
  • Block 6 Answers 279 In contrast to niacin, biotin (vitamin H) is an important cofactor for multisubunit enzymes that catalyze carboxylation reactions, an example of which is the synthesis and oxidation of fatty acids. A deficiency of biotin can lead to multiple symptoms, including depression, hallucinations, muscle pain, and dermatitis. Biotin is present in dietary food and is also produced by intestinal bacteria. Deficiencies of biotin are quite rare, but can occur in people who consume raw eggs. This is because egg white contains a heat-labile protein, avidin, which combines very tightly with biotin and prevents the absorption of biotin. Pyridoxine is a cofactor that participates in transamination reactions, decarboxylation reactions, and transsulfuration reactions. It is important in the synthesis of GABA and d-ALA. Deficiencies of pyridoxine can lead to decreased synthesis of GABA, which can cause convulsions in infants or a polyneuropathy in adults, or decreased ALA, which produces a hypochromic, sideroblastic anemia. Patients also develop cheilosis (inflammation and fissuring of the lips), angular stomatitis (cheilosis occurring at the corners of the mouth), glossitis (atrophy of the mucosa of the tongue), and seborrheic dermatitis. Pyridoxine deficiency may result from pregnancy or therapy with certain drugs, such as isoniazid, methyldopa, or levodopa. A common cause of B6 deficiency is chronic alcoholism. A deficiency of riboflavin (vitamin B2) is characterized by changes that occur around the mouth, namely cheilosis, angular stomatitis, and glossitis. Additionally, patients may develop seborrheic dermatitis of the face or genitalia, or blindness, which is the result of vascularization of the cornea (interstitial keratitis). Selenium is an antioxidant that is part of glutathione peroxidase, an enzyme that is found in red cells and white cells. As such, it prevents oxidative damage to both red blood cells and white cells. A deficiency of selenium leads to a form of dilated cardiomyopathy in children. This deficiency has been described in China and is called Keshan disease. 6-20. The answer is a. (Hardman, pp 1086–1089.) Intolerance of alcohol (disulfiram-like reaction) has been noted only with certain cephalosporins. Cephalosporins with the methylthiotetrazole side chain have been associated with a disulfiram-like reaction because the methylthiotetrazole group has a configuration similar to disulfiram, which blocks the metabolism of alcohol at the acetaldehyde step. Accumulation of acetaldehyde is associated with the symptoms. The methylthiotetrazole side chain also results in hypoprothrom-
  • 280 Clinical Vignettes for the USMLE Step 1 binemia by interfering with the synthesis of vitamin K–dependent clotting factors. 6-21. The answer is c. (Braunwald, p 1705.) Acute alcoholic hepatitis is characterized by the presence of Mallory bodies and WBCs in the liver biopsy specimen. Frequently, it shows fat and degenerating cells in the liver. Usually, with abstinence from alcohol, this will revert to a normal histologic pattern. However, on occasion, liver disease can progress despite abstinence. 6-22. The answer is b. (Hazzard, pp 1036–1037.) Alzheimer’s disease is a progressive, disabling, degenerative disease and the most common cause of dementia in the elderly. The most common presenting feature of Alzheimer’s disease is loss of memory. It is also usually accompanied by a gradual decline in intellectual function and impairment of orientation to time and place, judgment, problem solving, language, perception, and learning. Personality change often involves alteration or accentuation of premorbid traits, delusions, apathy, or depression. 6-23. The answer is a. (Hardman, pp 1247–1251.) 5-Fluorouracil is a pyrimidine antagonist that has a low neurotoxicity when compared with other fluorinated derivatives; however, its major toxicities are myelosuppression and oral or gastrointestinal ulceration. Leukopenia is the most frequent clinical manifestation of the myelosuppression. 6-24. The answer is d. (Afifi, pp 211, 227–231.) Inability to move the eyes up or down when they are displaced laterally would result from a lesion of the midbrain involving cranial nerve III. Because the somatomotor neurons of cranial nerve III supply, in part, the superior and inferior recti muscles as well as the inferior oblique muscle, cranial nerve III is responsible for up-and-down movements of the eye when they are positioned laterally. Recall that when the eye is positioned medially, it is the superior oblique that is innervated by cranial nerve IV that pulls the eye downward. 6-25. The answer is e. (Levinson, pp 150–152.) Ornithosis (psittacosis) is caused by Chlamydia psittaci. Humans usually contract the disease from
  • Block 6 Answers 281 infected birds kept as pets or from infected poultry, including poultry in dressing plants. Although ornithosis may be asymptomatic in humans, severe pneumonia can develop. Fortunately, the disease is cured easily with tetracycline. 6-26. The answer is e. (Carpenter, pp 174–175. Noback, p 209.) The abducens nerve (CN VI) innervates the lateral rectus muscle. Loss of innervation to the lateral rectus results in unopposed tension by the medial rectus, which produces internal strabismus. The oculomotor nerve (CN III) innervates the medial, superior, and inferior recti, the inferior oblique, and the levator palpebrae superioris muscles. Paralysis of this nerve would result in lateral deviation of the eye (external strabismus) accompanied by ptosis (drooping eyelid). In addition, mydriasis (dilated pupil) results from loss of function of the parasympathetic component of the oculomotor nerve. Damage to the trochlear nerve (CN IV) results in paralysis of the superior oblique muscle with impaired ability to direct the eye downward and outward. 6-27. The answer is d. (Katzung, pp 589–590.) Only gemfibrozil acts to lower triglycerides, probably because of increased lipolysis by lipoprotein lipase and decreased lipolysis inside adipocytes, causing a net movement of triglycerides into the cell. 6-28. The answer is b. (Kaplan, pp 361–362.) Hyperthyroidism (thyrotoxicosis) is a syndrome resulting from a chronic excess of thyroid hormone (thyroxine). It may be precipitated by acute emotional stress and may even develop within hours after an emotional trauma. It is an endocrine disorder and is almost always accompanied by mental changes—the patient may feel tense and hyperexcitable and may be emotionally labile, with inappropriate temper outbursts, crying spells, or euphoria. Distractibility, short attention span, and impaired recent memory may also be present. Severe hyperthyroidism may result in frank psychosis, delirium, coma, and death. Thyroid disorders are 7 times more frequent in women than in men; they occur most commonly in women in their third and fourth decades and in men at older ages. In contrast to the tense and hyperexcitable behaviors usually observed, a minority of patients, particularly the elderly, may be depressed, apathetic, and anorectic with chronic
  • 282 Clinical Vignettes for the USMLE Step 1 hyperthyroidism. Mildly hyperthyroid patients occasionally are misdiagnosed as having anxiety neuroses. Mental retardation in children is frequently associated with hypothyroidism, not hyperthyroidism, since normal brain development requires the thyroid hormone. 6-29. The answer is b. (Kandel, pp 82–83, 700–704.) In a peripheral neuropathy, there may be damage to either the myelin or the axon directly, although, more often, there is damage to the myelin. Because of myelin (or axonal) damage, there is a reduction (or loss) of conduction velocity. The disorder may affect both sensory and motor components of the peripheral nerve, thereby causing dysfunction in both the sensory and the motor processes associated with that nerve. Because there is peripheral neuronal damage, the motor loss will be reflected in a weakness, paralysis, or reflex activity associated with the affected muscle, as well as impairment of sensation. 6-30. The answer is b. (Guyton, pp 241–243.) The most obvious deleterious effect of a failing heart is the inability to pump enough blood to satisfy the energy requirements of all the tissues. Among the compensatory mechanisms that develop in response to heart failure is an increase in retention of fluid by the kidney. Increased retention of fluid causes the end-diastolic volume of the heart to increase, which, by the Starling mechanism, increases the strength of the heartbeat. However, two deleterious effects result from an increase in end-diastolic volume. A larger than normal end-diastolic volume causes an increase in end-diastolic pressure, which can lead to pulmonary edema. In addition, the large end-diastolic volume increases the wall stress that must be developed by the heart with each beat, and this increases the myocardial requirement of oxygen. The increase in contractility that results from the administration of a positive inotropic drug such as digoxin will allow the heart to produce the same force at a lower volume and thus eliminate the need for an increase in volume of fluid. 6-31. The answer is d. (Levinson, pp 75–77.) Recurrent severe infection is an indication for clinical evaluation of immune status. Live vaccines, including BCG attenuated from Mycobacterium tuberculosis, should not be used in the evaluation of a patient’s immune competence because patients with severe immunodeficiencies may develop an overwhelming infection
  • Block 6 Answers 283 from the vaccine. For the same reason, oral (Sabin) polio vaccine is not advisable for use in such persons. 6-32. The answer is a. (Katzung, p 499.) Of the listed antidepressants, only amitriptyline, a tricyclic, causes adverse effects related to blockade of muscarinic acetylcholine receptors. Both trazodone and amitriptyline cause adverse effects related to α-adrenoreceptor blockade. 6-33. The answer is d. (McPhee, p. 140; Braunwald, pp 2460–2468.) Numerous localized disorders and many systemic diseases can damage the spinal cord or the peripheral nerves. The pattern of pain, sensory loss, and sometimes weakness can help classify the disorder. A mononeuropathy involves pain/temperature and vibratory/joint position abnormalities, along the precise path of an individual nerve with associated weakness and pain. Mononeuropathy multiplex involves multiple noncontiguous peripheral nerves in a sequential fashion taking place over days to years. A radiculopathy involves a nerve root with dermatome distribution of both pain/temperature and vibratory/joint position abnormalities and weakness of the innervated muscles. Brown-Séquard’s syndrome also involves pain/temperature and vibratory/joint position abnormalities; however, the distribution is ipsilateral pain/temperature and contralateral vibratory/joint position abnormalities with an ipsilateral motor deficit. A polyneuropathy similarly involves pain/temperature and vibratory/joint position abnormalities with a stocking-glove distribution and painful paraesthesias. 6-34. The answer is e. (Howard, pp 213–242.) Many sputum specimens are cultured unnecessarily. Sputum is often contaminated with saliva or is almost totally made up of saliva. These specimens rarely reveal the cause of the patient’s respiratory problem and may provide laboratory information that is harmful. The sputum in question appears to be a good specimen. The pleomorphic Gram-negative rods are suggestive of Haemophilus, but culture of the secretions is necessary. 6-35. The answer is a. (Cotran, pp 926–928.) Functional islet cell tumors of the pancreas secrete specific substances that result in several syndromes. Pancreatic gastrinomas (tumors of the G cells of the pancreas) secrete gas-
  • 284 Clinical Vignettes for the USMLE Step 1 trin and are a cause of Zollinger-Ellison syndrome. This syndrome consists of intractable gastric hypersecretion, severe peptic ulceration of the duodenum and jejunum, and high serum levels of gastrin. The majority of gastrinomas are malignant. Insulinomas (tumors of β cells) are the most common islet cell neoplasm and are usually benign. Symptoms include low blood sugar, hunger, sweating, and nervousness. Glucagonomas (islet cell tumors of the α cells) secrete glucagon and are characterized by mild diabetes, anemia, venous thrombosis, severe infections, and a migratory, necrotizing, erythematous skin rash. δ cell tumors, which secrete somatostatin, produce a syndrome associated with mild diabetes, gallstones, steatorrhea, and hypochlorhydria. The majority of δ cell tumors are malignant. D1 tumors [also called vasoactive intestinal peptide tumors (VIPomas)] produce Verner-Morrison syndrome, which is characterized by explosive, profuse diarrhea with hypokalemia and hypochlorhydria. This combination of symptoms is referred to as pancreatic cholera. 6-36. The answer is b. (Murray, pp 627–661. Scriver, pp 3127–3164. Sack, pp 121–138. Wilson, pp 287–320.) Ferrous iron (Fe++) is the form absorbed in the intestine by ferritin, transported in plasma by transferrin, and stored in the liver in combination with ferritin or as hemosiderin. There is no known excretory pathway for iron, either in the ferric or ferrous form. For this reason, excessive iron uptake over a period of many years may cause hemochromatosis (235200), the likely diagnosis for this man. This is a condition of extensive hemosiderin deposition in the liver, myocardium, pancreas, and adrenals. The resulting symptoms include liver cirrhosis, congestive heart failure, diabetes mellitus, and changes in skin pigmentation. 6-37. The answer is b. (McPhee, pp 548–549. Braunwald, pp 2092–2095.) Mumps virus infection can directly affect the testicles, producing an orchitis, often very painful, and consequently infertility. Posttesticular causes are those that affect sperm transport, and pretesticular causes are those that affect the hormones that stimulate the testicles. 6-38. The answer is b. (Hardman, p 1077.) Oxacillin is classified as a penicillinase-resistant penicillin that is relatively acid-stable and, therefore, is useful for oral administration. Major adverse reactions include penicillin hypersensitivity and interstitial nephritis. With the exception of methicillin, which is 35% bound to serum proteins, all penicillinase-resistant
  • Block 6 Answers 285 penicillins are highly bound to plasma proteins. Oxacillin has a very narrow spectrum and is used primarily as an antistaphylococcal agent. 6-39 through 6-40. The answers are 6-39 c, 6-40 b. (Kandel, pp 298–304. Gilroy, pp 623–639, 640–642. Siegel, pp 871–883.) Myasthenia gravis is an autoimmune disease that causes cranial nerve and limb muscle weakness by producing antibodies that act against the nicotinic receptor at the neuromuscular junction. The result is that the action of nerve fibers that innervate skeletal muscle are affected, producing loss of the effects of ACh at the neuromuscular junction. The net result is a reduction of the size of the action potential in the muscle, producing a weakness in the affected muscle. This disorder is reversed by administration of drugs that inhibit the enzyme, acetylcholinesterase, that degrades ACh. Multiple sclerosis, ALS, and combined system disease (see the chapter entitled “The Spinal Cord”) involve damage to axons and/or nerve cells within the CNS, producing much more profound damage to motor functions and, in the case of combined system disease, damage to both motor and sensory systems. Muscular dystrophy is typically characterized, in part, by progressive weakness of muscles and degeneration of the muscle fibers. The other disorders listed all involve disorders affecting the CNS, and thus, the symptoms associated with these disorders differ significantly from those described in this case. Excessive release of ACh is not a realistic event that is likely to occur (except from the bite of a black widow spider). In theory, if it were to occur, there is no reason to believe that muscular weakness would be a symptom. Instead, there would be some rigidity and muscle spasms. 6-41. The answer is c. (Murray, pp 468–487. Scriver, pp 175–192. Sack, pp 245–257. Wilson, pp 151–180.) After the locus responsible for a genetic disease is mapped to a particular chromosome region, “candidate” genes can be examined for molecular abnormalities in affected individuals. The connective tissue abnormalities in Stickler syndrome (108300) make the COL2A1 collagen locus an attractive candidate for disease mutations, prompting analysis of COL2A1 gene structure and expression. Western blotting detects gene alterations that interfere with protein expression, while use of the reverse transcriptase–polymerase chain reaction (RT-PCR) detects alterations in mRNA levels. Each analysis should detect one-half the respective amounts of COL2A1 protein or mRNA in the case of a pro-
  • 286 Clinical Vignettes for the USMLE Step 1 moter mutation that abolishes transcription of one COL2A1 allele. Southern blotting detects nucleotide changes that alter DNA restriction sites, but this is relatively insensitive unless large portions of the gene are deleted. Fluorescent in situ hybridization (FISH) analysis using DNA probes from the COL2A1 locus is a sensitive method for detecting deletions of the entire locus, and DNA sequencing of the entire gene provides the gold standard for detecting any alteration in the regulatory or coding sequences. Nucleotide sequence changes are still subject to interpretation, since they may represent polymorphisms that do not alter gene function. Population studies and/or in vitro studies of gene expression are often needed to discriminate DNA polymorphisms from mutations that disrupt gene function. For any autosomal locus, the interpretation of molecular analyses is complicated by the presence of two homologous copies of the gene. 6-42. The answer is e. (April, p 613.) The patient has facial paralysis, which indicates injury to the facial nerve. A problem in the internal auditory meatus usually affects hearing and balance. That the superior salivatory nucleus is normal is indicated by normal lacrimation. Hence, the lesion must be distal to the origin of the greater superficial nerve at the genu of the facial nerve. However, absence of hyperacusis indicates that the branch to the stapedius muscle is functioning normally, and this fact suggests that the lesion is close to the stylomastoid foramen. Loss of taste and diminished salivation locate the lesion proximal to the origin of the chorda tympani nerve. If the lesion were distal to the stylomastoid foramen, taste and salivation would have been normal with facial paralysis as the only sign. 6-43. The answer is a. (Cotran, pp 961–962.) Many diseases involve hematuria, and a few of these diseases occur in the setting of an upper respiratory infection or of upper respiratory signs and symptoms. When hematuria follows within 2 days of the onset of an upper respiratory infection without skin lesions in a young patient, IgA nephropathy (Berger’s disease) should be considered. This disease involves the deposition of IgA in the mesangium of the glomeruli. Light microscopic examination may suggest the disease, but renal biopsy immunofluorescence (IF) must be performed to confirm it. This disorder may be the most common cause of nephritic syndrome worldwide. The hematuria may become recurrent, with proteinuria that may approach nephrotic syndrome proportions. Serum levels of IgA may be elevated. A small percentage of patients may progress to renal failure over a period of years. In contrast to Berger’s disease, a linear IF pat-
  • Block 6 Answers 287 tern suggests a type II hypersensitivity reaction, such as Goodpasture’s disease, while a granular pattern is seen with post-streptococcal glomerulonephritis (GN), membranous GN, focal segmental glomerulosclerosis, and membranoproliferative GN. Most positive immunofluorescence patterns involve IgG and C3, except that a granular IgM pattern is present in focal segmental glomerulosclerosis, while mesangial IgA is seen in IgA nephropathy (Berger’s disease). Lipoid nephrosis would have a negative IF pattern; that is, there would be no staining present. 6-44. The answer is e. (Hardman, pp 1269–1271.) Cisplatin causes acoustic nerve damage. Paclitaxel causes peripheral neuritis. Dosedependent pneumonitis and fibrosis are caused by bleomycin. Doxorubicin causes cardiac toxicity, which may lead to congestive heart failure. 5-Fluorouracil causes myelosuppression, stomatitis, and oral and gastrointestinal ulcerations. 6-45. The answer is b. (Levinson, pp 147–148, 153–155.) All the listed diseases except Q fever are tick-borne. The rickettsia C. burnetii causes Q fever, and humans are usually infected by aerosol of a sporelike form shed in milk, urine, feces, or placenta of infected sheep, cattle, or goats. Lyme disease is caused by a spirochete, Borrelia burgdorferi, and produces the characteristic lesion erythema chronicum migrans (ECM). The etiologic agent of Rocky Mountain spotted fever is R. rickettsia. It usually produces a rash that begins in the extremities and then involves the trunk. Two human forms of ehrlichiosis can occur: human monocytic ehrlichiosis (HME), caused by E. chaffeensis; and human granulocytic ehrlichiosis (HGE), caused by an as yet unnamed Ehrlichia. Ehrlichiosis was previously recognized only as a veterinary pathogen. HME infection is transmitted by the brown dog tick and A. americanum. HGE infection is transmitted by I. scapularis, the same tick that transmits Lyme disease. Both infections cause fever and leukopenia. A rash rarely occurs. E. chaffeensis infects monocytes, and HGE infects granulocytes; both organisms produce inclusion bodies called morulae. Francisella tularensis is a small, Gram-negative, nonmotile coccobacillus. Humans most commonly acquire the organism after contact with tissues or body fluid of an infected mammal or the bite of an infected tick. 6-46. The answer is b. (Cotran, pp 394–396. Rubin, pp 475–476.) Intestinal tapeworm (cestode) infections result from eating improperly prepared
  • 288 Clinical Vignettes for the USMLE Step 1 meat. T. saginata is acquired from ingesting contaminated beef, T. solium is acquired from contaminated pork, and D. latum is obtained from contaminated fish. The life cycles of these tapeworms involve larval stages in animals and worm stages in humans. If the contaminated meat contains the larval forms of these organisms, then they may develop into adult worms in the intestines of infected humans. These individuals generally remain asymptomatic, except that D. latum may cause a vitamin B12 deficiency. A very different disease results from humans eating the eggs of T. solium, which may be found in human feces. In this case, the eggs hatch into larva, which then penetrate the gut wall and disseminate via the bloodstream to lodge in different organs. There they encyst and differentiate into cysticerci. Multiple cysticerci in the brain produce a “Swiss cheese” appearance grossly, and microscopically a scolex (the head of the worm) is found with hooklets. This disease is called cysticercosis. Another cestode, E. granulosa, is the cause of hydatid disease in humans. Individuals become infected by eating the tapeworm eggs. Patients are usually sheep herders who get the eggs from their dogs. Larvae released from the eggs disseminate most often to the liver (75%), but they may also travel to the lungs or skeletal muscle. They form large, slowly growing, unilocular cysts that contain multiple scolices. Toxocara species, such as T. canis and T. cati, are one cause of visceral larval migrans. This disease is characterized by infection of visceral organs by helminthic larvae. The typical patient is a young child who develops hypereosinophilia and hypergammaglobulinemia. Ocular manifestations of toxocariasis are common, especially the loss of vision in one eye in a child. Note that this disease is different from cutaneous larva migrans, which is caused by the larval forms of the hookworms and Strongyloides stercoralis. 6-47. The answer is a. (Braunwald, p 1699.) The most serious consequences of chronic hepatitis B and C infections are hepatoma and cirrhosis. Complications of cirrhosis may occur, resulting in liver failure. Chronic hepatitis is not a risk factor for adenoma, cholangitis, lymphoma, or hemochromatosis. 6-48. The answer is c. (McPhee, pp 548–549. Braunwald, pp 2092– 2095.) Posttesticular causes of infertility are those that affect sperm transport, such as penile anatomic defects including hypospadias and epispadias. Other posttesticular causes of infertility include genital tract infections, retro-
  • Block 6 Answers 289 grade ejaculation, and antibodies to sperm or seminal plasma. Pretesticular causes are those that affect the hormones that stimulate the testicles, and testicular causes are those with a direct effect on the testicles. Idiopathic causes represent those causes that are likely genetic and not elsewhere classified. 6-49. The answer is e. (Cotran, pp 1333–1334.) The degenerative diseases of the CNS are diseases that affect the gray matter and are characterized by the progressive loss of neurons in specific areas of the brain. In Parkinson’s disease, characterized by a masklike facial expression, coarse tremors, slowness of voluntary movements, and muscular rigidity, there is degeneration and loss of pigmented cells in the substantia nigra, resulting in a decrease in dopamine synthesis. Lewy bodies (eosinophilic intracytoplasmic inclusions) are found in the remaining neurons of the substantia nigra. The decreased synthesis of dopamine by neurons originating in the substantia nigra leads to decreased amounts and functioning of dopamine in the striatum. This results in decreased dopamine inhibition and a relative increase in acetylcholine function, which is excitatory in the striatum. The effect of this excitation, however, is to increase the functioning of GABA neurons, which are inhibitory. The result, therefore, is increased inhibition or decreased movement. The severity of the motor syndrome correlates with the degree of dopamine deficiency. Therapy may be with dopamine agonists or anticholinergics. 6-50. The answer is b. (Levinson, pp 145–147.) This patient appears to have primary syphilis as evidenced by a penile chancre that was not tender. One of the differences between syphilis and herpes simplex virus (HSV) is that an HSV lesion is excruciatingly painful. Treponemal organisms may be seen microscopically in the lesion if the lesion is scraped. If not treated, the chancre will disappear and the patient will be asymptomatic until he/she exhibits the signs/symptoms of secondary syphilis, which include a disseminated rash and systemic involvement such as meningitis, hepatitis, or nephritis. There are two kinds of tests for the detection of syphilis antibodies: nonspecific tests such as the RPR and VDRL, and specific tests such as the FTA, TPHA (Treponema pallidum hemagglutination test), and the MHTP (microhemagglutination-T. pallidum). The difference is that the nonspecific tests use a cross-reactive antigen known as cardiolipin, while the specific tests use a T. pallidum antigen. Although the nonspecific tests
  • 290 Clinical Vignettes for the USMLE Step 1 are sensitive, they lack specificity and often cross-react in patients who have diabetes, hepatitis, infectious mononucleosis, or who are pregnant. Some patients, especially those with autoimmune diseases, will have both nonspecific (RPR) and specific tests (FTA) positive. Resolution of such a situation can be done by molecular methods for T. pallidum such as PCR, or by the immobilization test using live spirochetes and the patient’s serum. In the TPI test, the spirochetes will die in the presence of specific antibody.
  • BLOCK 7 Answers 7-1. The answer is a. (Cotran, p 176.) Sexual ambiguity arises when there is disagreement between the various ways of determining sex. Genetic sex is determined by the presence or absence of a Y chromosome. Gonadal sex is based upon the histologic appearance of the gonads. Ductal sex depends on the presence of derivatives of the Müllerian or Wolffian ducts. Phenotypic or genital sex is based on the appearance of the external genitalia. True hermaphroditism refers to the presence of both ovarian and testicular tissue. Pseudohermaphroditism is a disagreement between the phenotypic and gonadal sex. A female pseudohermaphrodite has ovaries but external male genitalia, while a male pseudohermaphrodite has testicular tissue, resulting from an XY genital sex karyotype, but female external genitalia. Female pseudohermaphroditism results from excessive exposure to androgens during early gestation; most often this is the result of congenital adrenal hyperplasia. Male pseudohermaphroditism results from defective virilization of the male embryo, most commonly caused by complete androgen insensitivity syndrome, also called testicular feminization. Kallmann’s syndrome results from a lack of embryonic migration of cells from the olfactory bulb to the hypothalamus and is characterized by primary amenorrhea, lack of secondary sex characteristics, and decreased sense of smell (hyposmia). Laboratory findings include decreased GnRH, LH, and FSH. Mixed gonadal dysgenesis consists of one well-defined testis and a contralateral streak ovary. It is a cause of ambiguous genitalia in the newborn. Turner’s syndrome, which has a 45,XO karyotype, is characterized by a female phenotype and bilateral streak ovaries. 7-2. The answer is d. (Levinson, pp 153–155.) Most rickettsial diseases are transmitted to humans by way of arthropod vectors. The only exception is Q fever, which is caused by C. burnetii. This organism is transmitted by inhalation of contaminated dust and aerosols or by ingestion of contaminated milk. 291 Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  • 292 Clinical Vignettes for the USMLE Step 1 7-3. The answer is b. (Brust, p 246.) The middle cerebral artery supplies a large portion of cerebral cortex, including portions of the frontal, parietal, and temporal lobes. These regions include the Broca’s and Wernicke’s areas and the precentral motor and postcentral sensory regions. Decreased blood flow in these regions explains the observed motor and sensory deficits. The anterior choroidal artery is a branch of the internal carotid artery and is primarily distributed to the basal ganglia, hippocampus, and choroid plexus of the lateral ventricle. The posterior communicating artery connects the internal carotid and vertebral arterial systems. The ophthalmic artery is a direct branch of the internal carotid artery that enters the orbit along with the optic nerve. Although the anterior cerebral artery has a wide distribution and anastomoses with branches of both the middle and posterior cerebral arteries, it primarily supplies medial and superior portions of the cortex. 7-4. The answer is d. (Simon, pp 163–164.) In this case, there is a loss of superficial abdominal reflexes, which require that spinal segments T8–T12 are intact. The test for these reflexes is to stroke a quadrant of the abdominal wall with an object such as a wooden stick. The normal response is for the muscle of the quadrant stimulated to contract and for movement of the umbilicus in the direction of the stimulus. 7-5. The answer is a. (Cotran, p 1129.) Both oligodendroglioma and craniopharyngioma show calcification fairly frequently; oligodendroglioma is often located in the frontal lobe, whereas craniopharyngioma occurs around the third ventricle and demonstrates suprasellar calcification. CT scan and particularly MRI are essential in diagnosis. Patchy intracerebral calcification may develop in tuberous sclerosis, an autosomal dominant disease characterized by the triad of epilepsy, mental retardation, and facial skin lesions (multiple angiofibromas). In addition, subependymal gliosis, cardiac rhabdomyoma, renal angiomyolipoma, and periungual fibroma occur. Calcification of the basal ganglia occurs in about 20% of patients with chronic hypoparathyroidism, which sometimes leads to a Parkinsonian syndrome. 7-6. The answer is c. (Braunwald, p 1688.) The serologic pattern in this case is a person who has recovered from HBV infection. They possess antiHBs, the protective antibody in HBV infection, IgG anti-HBc, and anti-
  • Block 7 Answers 293 HBc. The anti-HBc may be positive or negative in persons who recover from HBV. 7-7. The answer is c. (Hardman, p 810.) Digitalis inhibits Na+,K+-ATPase and, hence, decreases myocyte Na pumping, resulting in a relative reduction of Ca expulsion from Na-Ca exchange. The consequent increase in free Ca in the cell causes an increased intensity of interaction between actin and myosin filaments and enhanced contractility. 7-8. The answer is c. (Levinson, pp 143–144.) The symptoms of Legionnaires’ disease are similar to those of mycoplasmal pneumonia and influenza. Affected persons are moderately febrile, complain of pleuritic chest pain, and have a dry cough. Unlike Klebsiella and Staphylococcus, Legionella pneumophila exhibits fastidious growth requirements. Charcoal yeast extract agar either with or without antibiotics is the preferred isolation medium. While sputum may not be the specimen of choice for Legionella, the discovery of small Gram-negative rods by direct fluorescent antibody (FA) technique should certainly heighten suspicion of the disease. L. pneumophila is a facultative intracellular pathogen and enters macrophages without activating their oxidizing capabilities. The organisms bind to macrophage C receptors, which promote engulfment. 7-9. The answer is b. (Moore & Dalley, p 15.) The flexor pollicis brevis has two heads and there is a sesamoid bone associated with each of the tendons of these heads. Sesamoid bones are isolated islands of bone that may occur in tendons passing over joints. The patella is the classic example. The adductor pollicis also has two heads (transverse and oblique), but they are not associated with sesamoid bones. 7-10. The answer is d. (Braunwald, p 77.) This syndrome is called pseudoclaudication. It may also occur at times with exertion, thus causing confusion with peripheral vascular disease. Nerve impingement by osteoarthritis and by degenerative disk disease tends to give a radicular pattern to the discomfort. 7-11. The answer is d. (Baum, pp 220–221.) Temporomandibular disorder (TMD) involves pain in the oral cavity and grinding of the teeth. It affects either the jaw and/or the muscles in the face, head, neck, and shoul-
  • 294 Clinical Vignettes for the USMLE Step 1 ders. Anxiety and depression are major causal links in promoting grinding of the teeth both during the day and at night. This action produces chronic pain even without the jaw moving or the teeth grinding. The physiologic or neurologic etiology is still not clear, but studies have estimated that between one-third and one-half of the general population suffers from TMD. Less than 5% of these sufferers seek medical attention. Emotional factors such as depression, anxiety, distress, and sensitivity to pain are particularly important in developing and maintaining the chronic pain. Psychosocial efforts to reduce the stress and depression show moderate success, as have dental and general pain clinics where patients are educated about the disorder and taught behavioral techniques to relax and reduce the pain, through biofeedback. Psychosocial therapy has also been successfully combined with selected antidepressants to help reduce TMD. 7-12. The answer is a. (Cotran, pp 805–811.) The causes of diarrhea are numerous, and diarrhea may be broadly classified into multiple categories including secretory, osmotic, and exudative. Both secretory and exudative diarrhea may have infectious causes. Several viruses may cause secretory diarrhea. Rotavirus is a major cause of diarrhea in children between the ages of 6 and 24 months. Clinical symptoms consisting of vomiting and watery (secretory) diarrhea begin about 2 days after exposure. Bacterial enterocolitis may be related to either the production of performed toxins, such as with Vibrio cholerae and enterotoxigenic E. coli (a major cause of “traveler’s diarrhea”), or it may be related to bacterial invasion of the colon, as seen with salmonella and shigella. E. histolytica is a cause of amebiasis and is endemic in underdeveloped countries. It characteristically produces flask-shaped ulcers in the colon and may embolize to the liver, where it produces amebic liver abscesses. Lactase deficiency, a cause of osmotic diarrhea, is very rarely a congenital disorder, but much more commonly is an acquired disorder seen in adults that results in malabsorption of milk and milk products. The onset of symptoms from ulcerative colitis is most commonly apparent between the ages of 20 and 25 years. 7-13. The answer is d. (Hazzard, pp 125–141, 154, 177–184.) A major problem in attempting to provide health care for the elderly is understanding and counteracting some of the common stereotypes of aging. Although it is generally true that all five senses tend to decline in old age, it is not true that most elderly people feel miserable most of the time. In fact, recent
  • Block 7 Answers 295 studies show that the majority of the aged see themselves as being as happy as they were when they were younger. Boredom and lack of meaningful activity do become major factors with some aged, however. Another misconception is that a high percentage of the aged population live in longstay institutions, such as nursing homes, mental hospitals, and homes for the aged. Actually, only about 5% of persons 65 and over, and about 10% of persons age 75 and over, are in long-stay institutions. Attempting to retain one’s social, physical, and cognitive independence is a dominating factor and priority among the aged. Also, contrary to the stereotype that older drivers have a high automobile accident rate, older drivers have about the same accident rate per person as middle-aged drivers and a lower rate than drivers under age 30. By age 85, however, the crash rate is highest per mile driven. Longitudinal research has demonstrated that personality traits are highly stable after about age 30. 7-14. The answer is e. (Adams, pp 246–247.) In one form of retinitis pigmentosa, there is a genetic defect with respect to rhodopsin. The result of this defect is the production of defective opsin. As a consequence, rod cells are affected, leading to a reduced response to light. However, central vision is spared as are cone cells. Central nervous system (CNS) neurons such as those located in area 17 are not directly affected and vision is not totally lost. 7-15. The answer is c. (Murray, pp 627–661. Scriver, pp 3897–3964. Sack, pp 121–138. Wilson, pp 287–320.) Hemorrhagic disease of the newborn is caused by poor transfer of maternal vitamin K through the placenta and by lack of intestinal bacteria in the infant for synthesis of vitamin K. The intestine is sterile at birth and becomes colonized over the first few weeks. Because of these factors, vitamin K is routinely administered to newborns. Deficiencies of the fat-soluble vitamins A, E, D, and K can occur with intestinal malabsorption, but avid fetal uptake during pregnancy usually prevents infantile symptoms. Hypervitaminosis A can cause liver toxicity but not bleeding, and deficiencies of E (neonatal anemia) or C (extremely rare in neonates) have other symptoms besides bleeding. 7-16. The answer is d. (Ryan, p 115.) The initial response to a new infection is with an IgM class antibody. IgM develops quickly and usually disappears within a few months. The secondary response is IgG and reflects the patient’s immune status or, in the case of chickenpox, a vaccination given.
  • 296 Clinical Vignettes for the USMLE Step 1 7-17. The answer is b. (Sierles, pp 292–296. Wedding, pp 260–265.) The husband in the question is using a strong denial mechanism of defense. In the early stages of alcohol abuse denial often involves not recognizing the obvious problem. It soon becomes a major defense reaction, especially as the person begins to recognize within himself that his own attempts to control or resolve the alcohol problem are woefully inadequate, nor can he control some of the underlying psychosocial problems. Initial rationalization soon turns into strong denial. It is somewhat analogous to smoking addiction when a smoker rationalizes that she can quit any time she wants, and then begins to realize she can’t. Unfortunately in cases of alcohol abuse, the spouse usually waits an average of seven years after gross evidence of alcoholic behavior before seeking help. This puts the physician tremendously behind in attempting to help the patient, the family, or the community. In many medical schools very little is taught about substance abuse. Consider the denial being exercised in the medical school setting. While only 5% of medical students smoke cigarettes, 80% use alcohol at least twice weekly, and 16% consume an average of more than six drinks each time, also known as binge drinking. Other options in the question include rationalization (unacceptable feelings or facts become more tolerable by explaining them away), projection (attributing your own unacceptable thoughts or feelings to someone else), displacement (redirecting an emotion from the original object to another one), and reaction formation (adopting an attitude or behavior that is the opposite of your own unconscious feelings). 7-18. The answer is c. (Katzung, pp 778–780.) Clarithromycin is a macrolide antibiotic. It can inhibit cytochrome P450. This could lead to an increase in concentration of drugs that are metabolized by cytochrome P450 and are given simultaneously with clarithromycin. When given with terfenadine, an antihistaminic agent, the interaction may lead to cardiac arrhythmias. 7-19. The answer is a. (Brust, pp 210–213.) The nucleus ambiguus, along with special visceral efferent (SVE) components of CN IX, X, and XI, is a column of lower motor neurons that innervate muscles of the pharynx, larynx, and palate. Damage to this nucleus results in loss of the gag reflex, difficulty in swallowing, and hoarseness. The lateral spinothalamic tract passes through the medulla and carries
  • Block 7 Answers 297 sensory information (pain and temperature) from the contralateral extremities and trunk. Similarly, the spinal tract of CN V carries pain and temperature sensation from the ipsilateral face. Descending sympathetic pathways course through the medulla to reach the intermediolateral cell column of the spinal gray matter. Damage to these fibers would result in loss of ability to dilate the pupil (meiosis), drooping eyelid (ptosis), and loss of sweating ipsilaterally (hemianhydrosis). Damage to nerve fibers passing to and from the cerebellum via the inferior cerebellar peduncle would result in intention tremor and lack of coordination. 7-20. The answer is a. (Sierles, pp 94–97.) The most powerful biopsychosocial predictor of prevalence of illness and morbidity and mortality rates is socioeconomic status (SES). Persons of lower SES have a significantly higher prevalence of obesity, chronic illnesses, hypertension, and coronary artery disease. This can be attributed to multiple factors, including lack of access to medical care, lack of resources to seek medical care, living and working in a high-risk environment, dietary deficiencies, lack of educational background, lack of responsiveness of physicians to patients of lower SES and their problems, and the general lack of societal and political concern with the health of the poor. Iatrogenic illness is not as frequent in persons of lower SES because they have less contact with the remedies of physicians and medical technology. 7-21. The answer is c. (Cotran, pp 336, 379–380. Rubin, pp 436–438.) Cryptococcosis is caused by Cryptococcus neoformans, an encapsulated yeast (not dimorphic) that infects the central nervous system, primarily in immunocompromised patients. The soil-dwelling yeast is inhaled, but lung involvement tends to be mild in individuals who are not immunodeficient. Diagnosis of cryptococcal meningitis is achieved by finding encapsulated yeasts in CSF preparations. The capsule can be seen with a mucicarmine stain, or it can be negatively stained using india ink. The CSF and serum should also be tested for cryptococcal antigen by the latex cryptococcal agglutination test (LCAT), which is positive in more than 90% of cases. Cryptococcal meningitis varies from a chronic inflammatory and granulomatous infection to a noninflammatory meningitis with numerous yeasts massed, sometimes forming cystic “soap bubble” lesions in the brain. Do not confuse cryptococcus with cryptosporidium. Cryptosporidium parvum is a protozoan parasite that may cause a transient diarrhea in immunocom-
  • 298 Clinical Vignettes for the USMLE Step 1 petent individuals or a chronic diarrhea in patients with AIDS (cryptosporidiosis). Histologically, sporozoites may be found attached to the surface of intestinal epithelial cells. They are best seen with an acid-fast stain. Chromomycosis is a chronic infection of the skin that is produced by an organism that appears as a brown, thick-walled sphere (“copper penny”) in tissue sections. Coccidioidomycosis is a mycotic infection caused by inhalation of the arthrospores of the dimorphic fungus C. immitis. Within the lung the spores enlarge to form large spherules (sporangia) that become filled with many small endospores. The cyst ruptures, releasing the endospores. Unruptured spherules incite a granulomatous reaction, while the endospores cause a neutrophilic response. Paracoccidioidomycosis (South American blastomycosis) is a chronic granulomatous infection caused by Paracoccidioides brasiliensis, a dimorphic fungus seen in tissues as a large central organism having peripheral oval budding. This histologic appearance is described as being similar to a mariner’s wheel. 7-22. The answer is c. (Hardman, pp 813–814.) Digoxin is used in AF to slow the ventricular rate, not usually the AF itself. Digoxin acts to slow the speed of conduction, increase the atrial and AV nodal maximal diastolic resting membrane potential, and increase the effective refractory period in the AV node, which prevents transmission of all impulses from the atria to the ventricles. It exerts these effects by acting directly on the heart and by indirectly increasing vagal activity. 7-23. The answer is 7-23-c. (Howard, pp 535–537, 754, 755, 789–791.) Borrelia burgdorferi, the causative agent of Lyme disease, elicits an acute antibody response. IgM appears within days to a few weeks following tick bite, and IgG appears a few weeks later. IgG persists, IgM does not. Crossreactions occur with other treponemes. Fifth disease is a viral exanthem commonly seen in children 8 to 12 years old. Children are ill for a few days but recover without incident. Unfortunately, if a pregnant female acquires the disease in the first trimester of pregnancy, the fetus is at risk. The causative agent is thought to be a parvovirus (parvovirus B 19). Adults with no titer to varicella (VZV) are at risk for acquisition of chickenpox. If they are health care workers, there is additional risk in transmitting VZV to immunodeficient children. Antibodies to VZV are readily detected by both enzyme immunoassay (EIA) and fluorescent-antibody (FA) techniques.
  • Block 7 Answers 299 Delta agent is a recently discovered antigen associated with HBsAg. Its presence usually correlates with HBsAg chronic carriers who have chronic active hepatitis. EIA and radioimmunoassay (RIA) tests are available to detect antibodies to delta agent. SSPE is thought to be caused by a measles-related virus present in the central nervous system. Most SSPE patients show elevated measles virus antibodies in serum and CSF In patients with multiple sclerosis (MS), . lower CSF antibody titers have been observed, suggesting a possible etiologic role for measles virus in MS. 7-24. The answer is e. (Cotran, pp 904–907.) Inflammation of the pancreas (pancreatitis) may be either acute or chronic. Patients with acute pancreatitis typically present with abdominal pain that is associated with increased serum levels of pancreatic enzymes (amylase and lipase). Most cases of acute pancreatitis are associated with either alcohol ingestion or biliary tract disease (gallstones). Alcohol ingestion is the most common cause, and pancreatitis usually follows an episode of heavy drinking. Other, less frequent causes include hypercalcemia, hyperlipidemias, shock, infections (CMV and mumps), trauma, and drugs. Acute pancreatitis usually presents as a medical emergency. Symptoms of acute pancreatitis include abdominal pain that is localized to the epigastrium and radiates to the back, vomiting, and shock, the latter being the result of hemorrhage and kinins released into the blood. In severe pancreatitis there may be hemorrhage in the subcutaneous tissue around the umbilicus (Cullen’s sign) and in the flanks (Turner’s sign). Activation of the plasma coagulation cascade may lead to disseminated intravascular coagulopathy (DIC). Laboratory confirmation of pancreatic disease involves the finding of elevated serum amylase levels in the first 24 h and rising lipase levels over the next several days. Other pancreatic enzymes, such as trypsin, chymotrypsin, and carboxypeptidases, have not been as useful for diagnosis as have amylase and lipase. Complications seen in patients who survive the acute attack include pancreatic abscess formation, pseudocyst formation, or duodenal obstruction. Diabetes mellitus almost never occurs after a single attack of pancreatitis. 7-25. The answer is a. (Kingsley, pp 436–439; Purves, pp 225–227.) In astigmatism, the shapes of the cornea and possibly the lens become oblong, resulting in differences in the curvature of the lens along the long and short axes. Thus, astigmatism is corrected with a cylindrical lens.
  • 300 Clinical Vignettes for the USMLE Step 1 7-26. The answer is d. (Hardman, pp 1475–1476.) The incidence of adverse reactions with administration of prednisone is related to dosage and duration. Psychoses, peptic ulceration with or without hemorrhage (possibly leading to guaiac-positive stools), increased susceptibility to infection, edema, osteoporosis, myopathy, and hypokalemic alkalosis can occur. Other adverse reactions include cataracts, hyperglycemia, arrest of growth in children, and iatrogenic Cushing’s syndrome. The glucocorticoids are very effective drugs, but they can be very dangerous if not properly administered to a patient. 7-27. The answer is a. (Cotran, pp 14–15, 846–848.) The type and distribution of necrotic hepatocytes is often a clue as to the cause of the hepatic injury. Focal scattered necrosis is characteristic of viral hepatitis, but may also be seen with bacterial infections or other toxic insults. In focal necrosis, there is necrosis of single hepatocytes, or small clusters of hepatocytes, that is randomly located in some, but not all, of the liver lobules. In contrast, zonal necrosis refers to the finding of hepatocellular necrosis in identical areas in all of the liver lobules. There are basically three types of zonal necrosis. Centrilobular (acinar zone 3) necrosis is characteristic of ischemic injury (heart failure or shock), toxic effects (acetaminophen toxicity), carbon tetrachloride exposure, or chloroform ingestion. Drugs such as acetaminophen may be metabolized in zone 1 to toxic compounds that cause necrosis of zone 3 hepatocytes because they receive the blood from zone 1. Midzonal (zone 2) necrosis is quite rare, but may be seen in yellow fever, while periportal (zone 1) necrosis is seen in phosphorus poisoning or eclampsia. Submassive necrosis refers to liver cell necrosis that crosses the normal lobular boundaries. Classically the necrosis goes from portal areas to central veins (or vice versa) and is called bridging necrosis. If the hepatocellular necrosis is severe, it is called massive necrosis. This type of extensive necrosis is described as acute yellow atrophy, as grossly the liver appears soft, yellow, flabby, and decreased in size with a wrinkled capsule. It may be produced by hepatitis viruses (usually B or C), drugs, or chemicals. 7-28. The answer is a. (Guyton, p 440.) Beta-receptor-activated G proteins activate adenyl cyclase which catalyzes the formation of cAMP. cAMP activates protein kinase A, which phosphorylates phospholamban. Phosphorylated phospholamban releases the SR Ca2+ pump from inhibition. The sequestration of Ca2+ into the SR relaxes bronchiolar smooth muscle. In car-
  • Block 7 Answers 301 diac muscle, the sequestration of Ca2+ into the SR increases contractile strength because there is more Ca2+ available for release with each action potential. The depolarization of the SA node is caused by activation of the “funny” channel. This channel is activated at negative membrane potentials. The rate of its activation is increased when it is phosphorylated by protein kinase A. The transport of Ca2+ into skeletal muscle fibers is not affected by beta-receptors. Glycogenolysis in the liver is also increased by activated beta-receptors. In this case, the protein kinase A phosphorylates an enzyme called phosphorylase, which begins the process of glycogenolysis. 7-29. The answer is a. (Katzung, pp 697–698.) Mifepristone is structurally related to norethindrone. This compound is classified as a progesterone antagonist with weak agonistic properties. A single dose can function as an emergency postcoital contraceptive. It also can induce an abortion by causing contraction of the myometrium, which leads to detachment of the embryo. The drug is used in single or multiple doses followed by the administration of a prostaglandin to cause the abortion. Estrogens used alone or in combination with progestins have also proven effective in postcoital contraception. 7-30. The answer is c. (Levinson, pp 133–134.) Pasteurella multocida, a coccobacillary Gram-negative rod, is part of the normal mouth flora of dogs and cats. Consequently, many animal bites become infected with this microorganism. It is susceptible to penicillin, although multiresistant strains have been recovered from pigs and sheep. P multocida has four dif. ferent capsular types—designated A, B, D, and E—that correlate with disease production and host predilection; however, serotyping of these isolates is beyond the resources of most laboratories. 7-31. The answer is e. (Murray, pp 468–487. Scriver, pp 175–192. Sack, pp 245–257. Wilson, pp 151–180.) Gene therapy refers to a group of techniques by which gene structure or expression is altered to ameliorate a disease. Because of ethical and practical difficulties, germ-line therapy involving alterations of genes in primordial germ cells is not being explored in humans. Although germ-line genetic engineering is being performed in animals with the goals of improved breeding or agricultural yield, it alters the characteristics of offspring rather than the treated individuals. Somatic cell gene therapy is targeted to an affected tissue or group of tissues in the individual, and is most effective if stem cells such as bone marrow can be
  • 302 Clinical Vignettes for the USMLE Step 1 treated. Somatic cell gene therapy offers the hope of replacing damaged tissue without the rejection problems of transplantation. For autosomal recessive disorders, only one of the two defective alleles must be replaced or supplemented. 7-32. The answer is e. (Simon, pp 138–145.) Fibers from the left lateral geniculate destined for the upper bank of the calcarine fissure will mediate visual impulses associated with lower quadrants of the right visual fields for both eyes. This deficit is referred to as a right lower quadrantanopia. 7-33. The answer is d. (Sierles, p 405. Baum, pp 60–106.) While fearfulness, confusion, interpersonal conflict, and regression can generate stress that can have a direct effect on biologic responses, the loss of perceived control can take an even greater toll on the body. Excessive workload and job responsibility are stressful factors in terms of coronary risk, but they become even more powerful and biologically more destructive when they approach the limit of a person’s capacity to control his or her own work. Whether the stress is from employment, unemployment, finance, family, disease, or other factors, the threat of loss or actual loss of control over one’s being or activities appears to be the most devastating influence. Different people also have considerable variability in their responsiveness to a lack of or loss of control; this responsiveness then has a subsequent effect on their biologic processes. 7-34. The answer is c. (Guyton, pp 846–853.) Radiation treatment likely produced panhypopituitarism in the young child. Sexual maturation and growth during development will not occur because of low levels of GH, FSH, LF ILGF1, TSH and thyroid hormones, and gonadal hormones. The , cortisol response to stress is decreased due to low ACTH levels. A goiter cannot develop in the absence of TH. 7-35. The answer is a. (Hardman, pp 1460, 1464.) Cosyntropin is related to adrenocorticotropin. It corresponds to the first 24 amino acids of adrenocorticotropin. Cosyntropin complexes with a plasma membrane receptor that brings about the activation of adenylyl cyclase. Adenylyl cyclase catalyzes the formation of cAMP from ATP. In the cytoplasm, cAMP activates cAMP-dependent protein kinase, which participates in the phosphorylation of specific substrate proteins (e.g., enzymes). The phosphorylated protein eventually induces the particular response on the target cell.
  • Block 7 Answers 303 The cellular mechanism of action of hydrocortisone, a glucocorticoid, is also related to proteins but not by the enhancement of cAMP production. Hydrocortisone is transported by simple diffusion across the membrane of the cell into the cytoplasm and binds to a specific receptor. The steroidreceptor complex is activated and enters the nucleus, where it regulates transcription of specific gene sequences into ribonucleic acid (RNA). Eventually, messenger RNA (mRNA) is translated to form specific proteins in the cytoplasm that are involved in the steroid-induced cellular response. 7-36. The answer is b. (Moore & Dalley, pp 189, 350–351.) Flexion of the thigh would be least affected. The lesion involves the common iliac artery just proximal to its division into the internal and external iliac branches. Blood flow would be compromised to the external iliac artery and its downstream branches including the femoral, deep femoral, popliteal, tibial, fibular, and plantar arteries. Blood flow would also be diminished to branches of the internal iliac artery, including gluteal and visceral arteries. One of the most powerful flexors of the thigh is the psoas muscle, which originates from the lumbar vertebrae and receives most of its blood from the aorta and common iliac artery and thus would be unaffected by the lesion. 7-37. The answer is f. (Murray, pp 812–828. Scriver, pp 3–45. Sack, pp 1–40. Wilson, pp 23–98.) It is important that the pedigree be an accurate reflection of the family history and that information not be recorded unless specifically mentioned. Pedigree B in the figure omits the double line needed to indicate consanguinity, and pedigree C assumes that the father’s affected cousin is the offspring of his uncle rather than being unspecified. Pedigree F correctly illustrates the birth order (third) of the affected female (indicated by arrow) and the consanguinity (double line) represented by the first-cousin marriage. 7-38. The answer is c. (Braunwald, pp 2265, 2504–2505.) Alcohol withdrawal seizures are suspected because the man became shaky 2 days after admission in the hospital where he would not have access to alcoholic beverages, he has a macrocytosis consistent with folate deficiency due to alcoholism, and the diagnostic tests showed no underlying neurologic disease. The consumption of alcohol leads to excessive loss of magnesium in the urine and thus lowers seizure threshold. The AST level in general will
  • 304 Clinical Vignettes for the USMLE Step 1 increase more in the face of alcohol usage than will the ALT. The bulk of alcohol withdrawal seizures will occur within 5 days of the cessation of alcohol consumption. 7-39. The answer is b. (Braunwald, p 1688.) In this case, the patient has acute HBV infection signaled by the positive IgM anti-HBC. Because the HBsAg is negative, it likely is below the threshold for detection. The IgM response reflects recent infection. This serologic pattern does not fit with infection with any of the other hepatitis viruses. The symptoms and signs, lack of fever, and minimal abnormal findings on examination of the liver are consistent with the diagnosis of acute HBV. 7-40. The answer is d. (Hardman, pp 1080–1082. Katzung, pp 759–760.) Because of its long duration of action, benzathine penicillin G is given as a single injection of 1.2 million units intramuscularly every three or four weeks for the treatment of syphilis. This persistence of action reduces the need for repeated injections, costs, and local trauma. Benzathine penicillin G is also administered for group A, β-hemolytic streptococcal pharyngitis and pyoderma. For the later stages of syphilis, up to three weekly doses of the agent is administered. 7-41. The answer is d. (Murray, pp 505–626. Scriver, pp 4029–4240. Sack, pp 121–138. Wilson, pp 287–320.) Leukotrienes C4, D4, and E4 together compose the slow-reacting substance of anaphylaxis (SRS-A), which is thought to be the cause of asphyxiation in individuals not treated rapidly enough following an anaphylactic shock. SRS-A is up to 1000 times more effective than histamines in causing bronchial muscle constriction. Anti-inflammatory steroids are usually given intravenously to end chronic bronchoconstriction and hypotension following a shock. The steroids block phospholipase A2 action, preventing the synthesis of leukotrienes from arachidonic acid. Acute treatment involves epinephrine injected subcutaneously initially and then intravenously. Antihistamines such as diphenhydramine are administered intravenously or intramuscularly. 7-42. The answer is c. (Simon, pp 173–183.) The most likely cause of the condition in this patient is a cervical disk prolapse. This disorder would produce pain in the neck and arm, which increases with movement of the
  • Block 7 Answers 305 head. It would also cause loss of some sensation in the thumb and other fingers, as well as weakness in both finger extension and of the biceps reflex. Syringomyelia would produce bilateral segmental loss of pain and temperature. A knife wound completely severing the nerve would result in a functional loss similar to that experienced with an LMN paralysis. Polio results in loss of LMNs, thus also producing an LMN paralysis. One of the effects of AIDS is that it produces damage to the lateral and dorsal columns, resulting in the appearance of a UMN disorder. 7-43. The answer is c. (Hardman, p 1401.) Propylthiouracil is more strongly protein bound and crosses the placenta to a lesser degree than methimazole and is, therefore, the safest antithyroid drug in pregnancy. 7-44. The answer is a. (Levinson, pp 130–131.) Brucella are small, aerobic, Gram-negative coccobacilli. Of the four well-characterized species of Brucella, only one—B. melitensis—characteristically infects both goats and humans. Brucellosis may be associated with gastrointestinal and neurologic symptoms, lymphadenopathy, splenomegaly, hepatitis, and osteomyelitis. 7-45. The answer is d. (Cotran, pp 199–201.) A blood transfusion reaction is a type II hypersensitivity reaction that is mediated by antibodies reacting against antigens present on the surface of blood group antigens or irregular antigens present on the donor’s red blood cells. Type II hypersensitivity reactions result from attachment of antibodies to changed cell surface antigens or to normal cell surface antigens. Complement-mediated cytotoxicity occurs when IgM or IgG binds to a cell surface antigen with complement activation and consequent cell membrane damage or lysis. Blood transfusion reactions and autoimmune hemolytic anemia are examples of this form. Systemic anaphylaxis is a type I hypersensitivity reaction in which mast cells or basophils that are bound to IgE antibodies are reexposed to an allergen, which leads to a release of vasoactive amines that causes edema and broncho- and vasoconstriction. Sudden death can occur. Systemic immune complex reactions are found in type III reactions and are due to circulating antibodies that form complexes upon reexposure to an antigen (such as foreign serum), which then activates complement. This process is followed by chemotaxis and aggregation of neutrophils, which leads to release of lysosomal enzymes and eventual necrosis of tissue and cells. Serum sickness and Arthus reactions are examples of type III reactions. Delayed type hypersensitivity is type IV and is
  • 306 Clinical Vignettes for the USMLE Step 1 due to previously sensitized T lymphocytes, which release lymphokines upon reexposure to the antigen. This takes time—perhaps up to several days following exposure. The tuberculin reaction is the best-known example. T cell–mediated cytotoxicity leads to lysis of cells by cytotoxic T cells in response to tumor cells, allogenic tissue, and virus-infected cells. These cells have CD8 antigens on their surfaces. 7-46. The answer is c. (Waxman, pp 66–67, 203.) A lesion of the spinal canal that compresses the ventral commissure (syringomyelia) would interrupt ascending fibers crossing there but would not interfere with already crossed fibers ascending in the lateral spinothalamic tracts. Pain and temperature sensation above and below the level of the cord lesion would be preserved. The cell bodies of first-order afferent (sensory) neurons are located in the dorsal root ganglia. Their central processes enter the spinal cord and ascend one segment before synapsing with a second-order neuron in the dorsal horn. The central processes of second-order neurons cross in the ventral white commissure to the opposite side of the cord and ascend in the lateral spinothalamic tract to the ventral posterior lateral nucleus of the thalamus where they synapse with third-order neurons, which relay the message to cortical neurons of the postcentral gyrus of the parietal lobe. Lesions occurring unilaterally in a peripheral nerve would result in an ipsilateral deficit, whereas lesions in a crossed ascending pathway, in the thalamus, or in the cortex would result in contralateral deficits. 7-47. The answer is b. (McPhee, p. 140; Braunwald, pp 2460–2468.) Numerous localized disorders and many systemic diseases can damage the spinal cord or the peripheral nerves. The pattern of pain, sensory loss, and sometimes weakness can help classify the disorder. A mononeuropathy involves pain/temperature and vibratory/joint position abnormalities, along the precise path of an individual nerve with associated weakness and pain. Mononeuropathy multiplex involves multiple noncontiguous peripheral nerves in a sequential fashion taking place over days to years. A radiculopathy involves a nerve root with dermatome distribution of both pain/temperature and vibratory/joint position abnormalities and weakness of the innervated muscles. Brown-Séquard’s syndrome also involves pain/temperature and vibratory/joint position abnormalities; however, the distribution is ipsilateral pain/temperature and contralateral vibratory/joint position abnormalities with an ipsilat-
  • Block 7 Answers 307 eral motor deficit. A polyneuropathy similarly involves pain/temperature and vibratory/joint position abnormalities with a stocking-glove distribution and painful paraesthesias. 7-48. The answer is c. (Chandrasoma, pp 799–806. Cotran, pp 361–364.) Granuloma inguinale is a rare, sexually transmitted disease that is caused by Calymmatobacterium donovani, a small, encapsulated gram-negative bacillus. Infection results in a chronic disease that is characterized by superficial ulcers of the genital region. Regional lymph node involvement produces large nodular masses that develop extensive scarring. Specialized culture medium is available, but its use is not practical. Serologic tests are also not useful. Instead, histologic examination is used to demonstrate Donovan bodies, which are organisms within the cytoplasm of macrophages. They are seen best with silver stains or Giemsa’s stain. Chancroid is an acute venereal disease that is characterized by painful genital ulcers with lymphadenopathy. It is caused by Haemophilus ducreyi, a small, gramnegative bacillus. Gram stains of the suppurative lesions or cultures on specialized media may be used to make the diagnosis. Serologic tests are not useful. Neisseria gonorrheae, a gram-negative diplococcus, causes gonorrhea, an acute suppurative infection of the genital tract. In males it produces a purulent discharge (urethritis) and dysuria. In women, it may be asymptomatic (50%), or it may produce infection of the cervix with accompanying vaginal discharge, dysuria, and abdominal pain. Ascending infections in women can lead to salpingitis, tuboovarian abscess, and pelvic inflammatory disease (PID). Fitz-Hugh–Curtis syndrome refers to perihepatitis infection. In newborns, infection acquired during birth can produce a purulent conjunctivitis (ophthalmia neonatorum). This disease has been prevented due to prophylactic therapy to newborn infants. A Gram stain of the urethral or cervical exudate may reveal the intracytoplasmic gram-negative diplococci, or the exudate can be cultured on special media. Serologic tests are not useful. Characteristically, N. gonorrheae produces acid from glucose, but not from maltose or lactose. The spirochete T. pallidum, the causative agent of syphilis, has not been grown on any culture media; therefore, other means are available to aid in the diagnosis of syphilis. Dark-field or immunofluorescence examination may be used to detect organisms in the genital ulcers of primary syphilis. Antibodies to cardiolipin, a substance in beef heart that is similar to a lipoid released by T. pallidum, are used to screen for syphilis. This is the basis of both the
  • 308 Clinical Vignettes for the USMLE Step 1 VDRL and the rapid plasma reagin (RPR) tests; however, these screening tests are not totally specific. Chlamydia species are obligate intracellular parasites that form elementary bodies and reticulate bodies. The former are small, extracellular, and infectious, while the latter are intracellular and noninfectious. Three Chlamydia species are C. psittaci, C. pneumoniae, and C. trachomatis. The last causes several human diseases including trachoma, inclusion conjunctivitis, nongonococcal urethritis, and lymphogranuloma venereum (LGV). Specialized culture media and direct examination procedures are available to aid in the diagnosis of these diseases. The regional lymph nodes in patients with lymphogranuloma venereum have a characteristic histologic appearance typified by necrotizing granulomas forming stellate areas of necrosis. Trachoma is the leading cause of blindness in underdeveloped countries. It is a chronic infection of the conjunctiva that eventually scars the conjunctiva and cornea. Lymphogranuloma venereum is a sexually transmitted disease that is characterized by the formation of a genital ulcer with local necrotizing lymphadenitis. The skin test for LGV is the Frei test, which consists of intradermal injection of LGV antigen. C. psittaci is the causative agent of psittacosis (parrot fever). It produces a severe pulmonary disease and should be suspected in patients with a history of bird contact, such as pet shop workers or parrot owners. 7-49. The answer is b. (Braunwald, pp 2016, 2023–2030, 2033–2034.) The pattern and amount of radioiodine uptake on 123I scan is fundamental to the correct diagnosis of thyrotoxicosis. Low-uptake thyrotoxicosis can occur when there is destruction of the thyroid follicles with release of thyroid hormone, such as in subacute thyroiditis, which usually presents as an exquisitely painful gland. Iodine-induced hyperthyroidism, factitious hyperthyroidism, and painless (silent) thyroiditis also cause low-uptake thyrotoxicosis. 7-50. The answer is a. (Afifi, pp 30–34; Nolte, pp 18–21.) Damage to a nerve fiber proximal to its cell body will cause, among other changes, retrograde degeneration of the cell body. A number of changes occur in the neuron during the process of retrograde degeneration. The cell body initially shows some swelling and becomes distended. At the beginning of the degenerative process, there is an accumulation of mitochondria in the axoplasm at Ranvier’s nodes. The nucleus is then displaced toward the periph-
  • Block 7 Answers 309 ery of the cell. The Nissl granules break down, first in the center of the cell; later, the breakdown spreads outward. In addition, the axonal process distal to the site of the lesion will undergo degeneration. It should be noted that retrograde degeneration procedures were used experimentally prior to the advent of histochemical methods for identifying cell bodies of origin of given pathways in the CNS.
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  • BLOCK 8 Answers 8-1. The answer is a. (Hardman, p 1082. Katzung, pp 764–766.) The third-generation cephalosporin, ceftriaxone, and cefixime are considered first-line drugs in the treatment of gonorrhea because most strains of Neisseria gonococci are resistant to the penicillins. Amikacin and other aminoglycosides are used in serious infections caused by E. coli, Enterobacter, Klebsiella, and Serratia species. However, spectinomycin, which is related to the aminoglycosides, can be used as a backup drug for gonorrhea. 8-2. The answer is d. (Cotran, pp 864–867. Chandrasoma, pp 643–645.) Several clinical syndromes may develop after exposure to any of the viruses that cause hepatitis, including asymptomatic hepatitis, acute hepatitis, fulminant hepatitis, chronic hepatitis, and the carrier state. Asymptomatic infection in individuals is documented by serologic abnormalities only. Liver biopsies in patients with acute hepatitis, either the anicteric phase or the icteric phase, reveal focal necrosis of hepatocytes (forming Councilman bodies) and lobular disarray resulting from ballooning degeneration of the hepatocytes. These changes are nonspecific, but the additional finding of fatty change is suggestive of hepatitis C virus (HCV) infection. Clinically, acute viral hepatitis is classified into three phases. During the prodrome phase, patients may develop symptoms that include anorexia, nausea and vomiting, headaches, photophobia, and myalgia. An unusual symptom associated with acute viral hepatitis is altered olfaction and taste, especially the loss of taste for coffee and cigarettes. The next phase, the icteric phase, involves jaundice produced by increased bilirubin. Patients may also develop light stools and dark urine (due to disrupted bile flow) and ecchymoses (due to decreased vitamin K). The final phase is the convalescence phase. Fulminant hepatitis refers to massive necrosis and is seen in about 1% of patients with either hepatitis B or C, but very rarely with hepatitis A infection. The biggest risk for fulminant hepatitis is coinfection with both hepatitis B and D. Chronic hepatitis is defined as elevated serum liver enzymes for longer than 6 months. Patients may be either symptomatic or asymptomatic. 311 Copyright 2002 by The McGraw-Hill Companies, Inc. Click Here for Terms of Use.
  • 312 Clinical Vignettes for the USMLE Step 1 8-3. The answer is b. (Moore & Dalley, pp 546, 561.) Perforating branches of the deep femoral artery are the principal blood supply to the posterior thigh. The other arteries supply anterior, medial, and gluteal regions of the thigh. 8-4. The answer is d. (Simon, pp 138–145.) A neuritis involving the optic disk would affect the size of the visual field loss around the optic disk, which corresponds to the blind spot. In general, this kind of neuritis would expand somewhat the size of the blind spot but would cause no further visual loss. 8-5. The answer is a. (Ryan, pp 276–277.) The incidence of group B streptococcal disease (GBS) is 1–3 cases per 1000 births. Neonates acquire the disease during birth from mothers who harbor the organism. Risk factors include prematurity, premature rupture of membranes, and group B streptococcal carriage. The Gram’s stain of cerebrospinal fluid is a rapid test for GBS disease. Although sensitive, the Gram’s stain requires experience to differentiate these streptococci from other Gram-positive cocci. Latex tests for GBS antigen are also available, but sensitivity in CSF is not significantly higher than the Gram’s stain. GBS can be reduced by intrapartum administration of penicillin. Experimentally, GBS polysaccharide vaccines have also been used. Screening pregnant females early in pregnancy probably offers little advantage because of the possible acquisition of GBS late in the pregnancy. There has been speculation concerning the pathogenesis of GBS. These include failure to activate complement pathways and immobilization of polymorphonuclear leukocytes (PMNs) due to the inactivation of complement C5A, a potent chemoattractant. While GBS is relatively more resistant to penicillin than group A streptococci, the great majority of GBS isolates are still penicillin-susceptible. An aminoglycoside such as gentamicin may be added to GBS treatment regimens due to the relative reduced susceptibility of some strains. 8-6. The answer is d. (Braunwald, pp 71, 1917–1918.) There is a high correlation between temporal arteritis and the occurrence of polymyalgia rheumatica, and this would explain the proximal muscle girdle pain that is a frequent finding in temporal arteritis. This disease is an inflammation of the small arteries although there may be some involvement of the middle-sized arteries. The only laboratory test to attempt to confirm your diagnosis is to
  • Block 8 Answers 313 obtain an ESR, which should be elevated above 100. Definitive diagnosis is by temporal artery biopsy. Treatment with steroids prevents the occurrence of blindness as a complication. The elevated level of alkaline phosphatase is an incidental finding, perhaps because of alcohol consumption. 8-7. The answer is k. (Katzung, p 390.) Long-acting benzodiazepams such as diazepam are useful in alcohol withdrawal. Its active metabolite is eliminated slowly, thereby increasing its duration of action. In patients with liver disease, short-acting agents might prove effective if they are metabolized to inactive water-soluble metabolites (e.g., oxazepam). Triazolam would be useful because of its short duration of action. 8-8. The answer is a. (Moore & Dalley, p 673.) A mnemonic device for remembering the order in which the soft tissues overlie the cranium is SCALP: Skin, Connective tissue, Aponeurosis, Loose connective tissue, and Periosteum. The scalp proper is composed of the outer three layers, of which the connective tissue contains one of the richest cutaneous blood supplies of the body. The occipitofrontal muscle complex inserts into the epicranial aponeurosis, which forms the intermediate tendon of this digastric muscle. This structure, along with the underlying layer of loose connective tissue, accounts for the high degree of mobility of the scalp over the pericranium. If the aponeurosis is lacerated transversely, traction from the muscle bellies will cause considerable gaping of the wound. Secondary to trauma or infection, blood or pus may accumulate subjacent to the epicranial aponeurosis. 8-9. The answer is b. (Murray, pp 627–661. Scriver, pp 2275–2296. Sack, pp 121–138. Wilson, pp 287–320.) An elevation of pyruvate and a deficiency of acetyl CoA suggest a deficiency of pyruvate dehydrogenase (PDH). This multisubunit enzyme assembly contains pyruvate dehydrogenase, dihydrolipoyl transacetylase, dihydrolipoyl dehydrogenase, and two enzymes involved in regulation of the overall enzymatic activity of the complex. PDH requires thiamine pyrophosphate as a coenzyme, dihydrolipoyl transacetylase requires lipoic acid and CoA, and dihydrolipoyl dehydrogenase has an FAD prosthetic group that is reoxidized by NAD+. Biotin, pyridoxine, and ascorbic acid are not coenzymes for PDH. An ATP-dependent protein kinase can phosphorylate PDH to decrease activity, and a phosphatase can activate PDH. Increases of ATP, acetyl CoA, or NADH
  • 314 Clinical Vignettes for the USMLE Step 1 (increased energy charge) and of fatty acid oxidation increase phosphorylation of PDH and decrease its activity. PDH is less active during starvation, increasing pyruvate, decreasing glycolysis, and sparing carbohydrates. Free fatty acids decrease PDH activity and would not be appropriate therapy for PDH deficiency. PDH deficiency (246900, 312170) exhibits genetic heterogeneity, as would be expected from its multiple subunits, with autosomal and X-linked recessive forms. The infant also could be classified as having Leigh’s disease (266150), a heterogenous group of disorders with hypotonia and lactic acidemia that can include PDH deficiency. 8-10. The answer is d. (Gilroy, pp 612–628. Simon, pp 182–184.) GuillainBarré syndrome is an acute polyneuropathy whose occurrence frequently follows a respiratory infection. It results in myalgia of the lower limbs, loss of muscle tone and tendon reflexes, and some flaccidity. The disorder can also affect the seventh cranial nerve. The disorder can produce diffuse demyelination of the peripheral nerves with an increase in lymphocytes present at the sites of demyelination. The other disorders listed are generally progressive where eventual recovery without intervention is not known to occur. Myasthenia gravis and lumbar disk prolapse would not show demyelination and lymphocyte increases near the sites of demyelination. Multiple sclerosis involves central nervous system (CNS) structures; therefore, the constellation of symptoms would be different. As indicated earlier, MD is progressive with effects upon both proximal muscles and later in distal muscles. 8-11. The answer is c. (Hardman, pp 887, 889.) Bile acid-binding resins bind more than just bile acids, and binding of simvastatin to cholestyramine is the most likely mechanism for decreased GI absorption. Cholestyramine may also bind to several other drugs, including digoxin, benzothiadiazides (thiazides), warfarin, vancomycin, thyroxine (T4), and aspirin. Medications should be given one hour before or four hours after cholestyramine. 8-12. The answer is d. (Kaplan, p 52.) An earlier study by Pauline Bart argued that the role of full-time mother leaves women in a difficult and depressed state when their children reach adulthood and leave home. This was designated as the empty nest syndrome. Subsequent studies have shown that this conventional wisdom is misleading; that women
  • Block 8 Answers 315 report less stress; that many newlyweds visit or telephone their parents, use their cars, and so on; that with delayed marriage, getting children to leave home is becoming a bigger problem; that middle-aged women who had not launched their children reported much less positive self-concepts than those who had, especially in interpersonal relationships; and that, in general, women look forward to the freedom and opportunity acquired by having their children launched. The increase in divorce at this age is more often related to the departure’s unmasking of an empty marriage than to the empty nest syndrome. 8-13. The answer is c. (Cotran, pp 284–286.) There are several mechanisms through which proto-oncogenes (p-oncs) can become oncogenic (c-oncs). Normal cellular genes (proto-oncogenes) may become oncogenic by being incorporated into the viral genome (forming v-oncs), or they may be activated by other processes to form cellular oncogenes (c-oncs). These other processes include gene mutations, chromosomal translocations, and gene amplifications. Gene mutations, such as point mutations, are associated with the formation of cancers by mutant c-ras oncogenes. Chromosomal translocations are associated with the development of many types of cancers, one example of which is Burkitt’s lymphoma. The most common translocation associated with Burkitt’s lymphoma is t(8;14), in which the c-myc oncogene on chromosome 8 is brought in contact with the immunoglobulin heavy chain gene on chromosome 14. Two other examples of chromosomal translocations are the association of chronic myelocytic leukemia (CML) with t(9;22), which is the Philadelphia chromosome, and the association of follicular lymphoma with the translocation t(18;14). The former involves the proto-oncogene c-abl, which is rearranged in proximity to a break point cluster region (bcr) on chromosome 22. The resultant chimeric c-abl/bcr gene encodes a protein with tyrosine kinase activity. The t(18;14) translocation involves the bcl-2 oncogene on chromosome 18. Expression of the oncogene bcl-2 is associated with the prevention of apoptosis in germinal centers. Examples of associations that involve gene amplification include N-myc and neuroblastoma, c-neu and breast cancer, and erb-B and breast and ovarian cancer. Gene amplifications can be demonstrated by finding doublet minutes or homogenous staining regions. 8-14. The answer is c. (Hardman, p 890. Katzung, pp 588–589.) Only niacin improves levels of VLDL, HDL, and LDL and inhibits cholesterol syn-
  • 316 Clinical Vignettes for the USMLE Step 1 thesis. It also limits the progression of atherosclerosis by lowering circulating fibrinogen and increasing circulating tissue plasminogen activator (tPA). 8-15. The answer is b. (Katzung, p 411.) Severe hepatotoxicity of an idiosyncratic nature is associated with valproic acid. The risk is very high in the pediatric population, particularly in patients below the age of two. Fatalities generally occur within four months of treatment. Hepatotoxicity may be reversed in some individuals. 8-16. The answer is b. (Braunwald, p 1982.) The best screening test for suspected acromegaly is an IGF-1. Random growth hormone varies too much to be useful. IGF-1 is more consistent and does not fluctuate episodically throughout the day. TSH and prolactin may be abnormal but are not diagnostic of acromegaly. Fasting blood sugar may be elevated in this patient, but again it is not diagnostic. 8-17. The answer is e. (Baum, pp 230–234.) Sensory information alone (what one can expect to feel) has been found to be the most effective type of information. Coping information (e.g., teaching coping skills, ways to relieve pain and discomfort) is the next most effective because it provides the patient with some sense of control. Procedural information (what procedures will be done) makes the surgery more predictable, but does not address the sensations one should expect. The most effective reduction of stress is achieved by combining sensory and coping information so that the patient is able to predict when pain will occur, how it will feel, and how to cope with it. Studies confirm that it is important for the patient to be able to establish or retain some sense of control. 8-18. The answer is a. (Katzung, p 1124.) Decreased gastrointestinal absorption of ciprofloxacin occurs with antacids because of their ability to adsorb the fluoroquinolone. Other preparations containing divalent ions, such as iron, will impede fluoroquinolone absorption. 8-19. The answer is a. (Howard, pp 231–250.) Certain strains of staphylococci elaborate an enterotoxin that is frequently responsible for food poisoning. Typically, the toxin is produced when staphylococci grow on foods rich in carbohydrates and is present in the food when it is consumed. The resulting gastroenteritis is dependent only on the ingestion of toxin and not on bacterial multiplication in the gastrointestinal tract. Characteristic
  • Block 8 Answers 317 symptoms are nausea, vomiting, abdominal cramps, and explosive diarrhea. The illness rarely lasts more than 24 h. 8-20. The answer is d. ( Young, p 358. Junqueira, pp 440–441. Yen, pp 714–715.) The patient described in this question is probably pregnant. The delay in menstruation coupled with the presence of basophilic cells in a vaginal smear are clues. Ovulation is the midpoint of the cycle and should be more than a few days away. She is relatively young for the onset of menopause and there are no other symptoms. The vaginal epithelium varies little with the normal menstrual cycle. Exfoliative cytology can be used to diagnose cancer and to determine if the epithelium is under stimulation of estrogen and progesterone. The presence of basophilic cells in the smear with the Pap-staining method would indicate the presence of both estrogen and progesterone. The data suggest the maintenance of the corpus luteum (i.e., pregnancy). 8-21. The answer is e. (Murray, pp 412–434. Scriver, pp 3–45. Sack, pp 3–29. Wilson, pp 99–121.) The process of transduction involves the transfer of a portion of DNA from one bacterium to the chromosome of another bacterium by means of a viral infection. Conjugation is the transfer of a socalled male chromosomal DNA to the DNA of an acceptor, or female, bacterial cell. Colinearity defines the relationship between genes and proteins in that the sequence of amino acids in proteins is a result of the sequence of base triplets in template genes. Recombination is simply the exchange of sequences between two molecules of DNA. Transformation results when exogenous DNA fragments are incorporated into the chromosome of another organism, as in the transformation of pneumococcal bacteria that led Avery and McLeod to recognize the genetic significance of DNA. 8-22. The answer is c. (Gilroy, pp 199–211.) Multiple sclerosis is a demyelinating autoimmune disease that affects CNS function. This disorder produces a wide variety of symptoms, including sudden sensory dysfunction and loss, which affect vision and the somatosensory system, causing tingling, pain, and hypesthesia. Broad functional motor disturbances also occur, including weakness of the upper or lower limbs, UMN signs, and gait impairment. There is also bladder dysfunction as well as an increase in CSF protein and IgG synthesis. Diffuse cerebellar degeneration would produce gait ataxia and deficits in the accuracy of intentional movements. ALS would produce both a UMN and an LMN paralysis, which typ-
  • 318 Clinical Vignettes for the USMLE Step 1 ically does not extend to sensory functions. Likewise, a peripheral neuropathy would not produce UMN signs, visual deficits, and extensive motor disturbances as described in this case. A tumor of the prefrontal cortex would affect some cognitive and emotional functions, but it would not affect sensory processes such as vision and somatosensation, nor would it produce signs of a UMN disorder or muscle weakness. 8-23. The answer is a. (Hughes, pp 109–110.) Many people avoid taking action in an emergency situation. The farther away the bystander is and the more people present, the less likely is a bystander to get involved. One is more apt to help the more one knows what to do, the fewer people present, if one is a male, if the victim does not appear to be responsible for his or her mishap (e.g., stroke victim versus drunk), if the negative consequences to the bystander are minimal and the positive consequences reasonable, if the bystander’s freedom is not limited by helping, if the bystander is somehow forced to get involved, if someone else is acting as a helping model, and if the victim is dependent or without resources or has helped the bystander in the past. Altruism is most easily learned through positive reinforcement and imitation. 8-24. The answer is c. (Braunwald, p 160.) This is the typical Argyll Robertson pupil found in syphilis. The RPR (rapid plasma reagin), a nontreponemal antibody test for syphilis, will be positive. 8-25. The answer is e. (Katzung, p 116). High concentrations of atropine block all parasympathetic function. The patient usually presents with an array of symptoms and signs that include dry mouth, dilated pupils, tachycardia, red and hot skin, and delirium. Hyperthermia may occur, particularly in very young children. 8-26. The answer is d. (Murray, pp 452–467. Scriver, pp 3–45. Sack, pp 1–40. Wilson, pp 101–120.) The deadly mushroom A. phalloides has several toxins. A major toxin is α-amanitin, an octapeptide that inhibits mRNA synthesis by very tightly binding RNA polymerase II (DNA-dependent RNA polymerase). As little as one of the mushrooms (know as the deathcap, death-cup, or avenging angel) delivers a lethal dose of about 10 mg α-amanitin. Severe, irreversible liver damage occurs quickly, leading to death. At higher concentrations, the toxin can inhibit RNA polymerase III and tRNA synthesis. Polymerase I is unaffected. Since α-amanitin is effec-
  • Block 8 Answers 319 tive at concentrations of 10−9 to 10−8 M, it has been useful as a research tool for studying RNA polymerase function. 8-27. The answer is d. (Cotran, pp 387–388, 807–809.) Yersinia (formerly called Pasteurella) is an important genus of gram-negative bacilli that causes a wide variety of human and animal disease, ranging from plague (Y. pestis) to acute mesenteric lymphadenitis (Y. enterocolitica) in older children and young adults. Y. enterocolitica infections also occur in the terminal ileum in young adults, causing an ileitis that produces inflammation not unlike that seen in some stages of Crohn’s disease (regional enteritis). Since the organisms grow slowly on enrichment media, they may be overgrown by other coliforms at 37°C. The organisms may be isolated by means of cold enhancement at 4°C. 8-28. The answer is c. (Hardman, p 408.) Clozapine differs from other neuroleptic agents in that it can induce seizures in nonepileptic patients. In patients with a history of epileptic seizures for which they are not receiving treatment, stimulation of seizures can occur following the administration of neuroleptic agents because they lower seizure threshold and cause brain discharge patterns reminiscent of epileptic seizure disorders. 8-29. The answer is d. (Murray, pp 452–467. Scriver, pp 3–45. Sack, pp 1–40. Wilson, pp 101–120.) The gene that produces the deadly toxin of Corynebacterium diphtheriae comes from a lysogenic phage that grows in the bacteria. Prior to immunization, diphtheria was the primary cause of death in children. The protein toxin produced by this bacterium inhibits protein synthesis by inactivating elongation factor 2 (EF-2, or translocase). Diphtheria toxin is a single protein composed of two portions (A and B). The B portion enables the A portion to translocate across a cell membrane into the cytoplasm. The A portion catalyzes the transfer of the adenosine diphosphate ribose unit of NAD1 to a nitrogen atom of the diphthamide ring of EF-2, thereby blocking translocation. Diphthamide is an unusual amino acid residue of EF-2. 8-30 through 8-32. The answers are 8-30 d, 8-31 c, 8-32 b. (Gilroy, pp 587–589. Afifi, pp 163–165.) Taste associated with the anterior two-thirds of the tongue is mediated by the facial (cranial nerve VII) nerve. The geniculate ganglion contains the cell bodies associated with the sensory (gustatory) component of the seventh nerve. The somatic motor component of the sev-
  • 320 Clinical Vignettes for the USMLE Step 1 enth nerve mediates the muscles of facial expression. Thus, the sensory and motor components of the seventh nerve affected in this individual can be characterized as special visceral afferent (because this afferent contains chemoreceptors) and special visceral efferent (because the motor component innervates skeletal muscle and is derived from a branchial arch), respectively. 8-33. The answer is b. (Moore & Dalley, pp 541–542.) The saphenous nerve accompanies the great saphenous vein along the medial aspect of the leg and foot as far as the great toe. The superficial fibular nerve innervates the central portion of the dorsum of the foot. The sural cutaneous nerve innervates the lateral aspect of the foot. The medial and lateral plantar branches of the tibial nerve supply the sole of the foot. 8-34. The answer is b. (Murray, pp 412–434. Scriver, pp 3–45. Sack, pp 3–29. Wilson, pp 99–121.) The Ames test is a rapid and relatively inexpensive bacterial assay for determining mutagenicity of potential toxic chemicals. Since many chemical carcinogens are mutagenic, it seems obvious that damage to DNA is a central event in carcinogenesis as well as mutagenesis. Dr. Bruce Ames developed a tester strain of Salmonella that has been modified not to grow in the absence of histidine because of a mutation in one of the genes for the biosynthesis of histidine. Toxic chemicals that are mutagens are placed in the center of the plate and result in reversions of the original mutations, so that histidine is synthesized and the mutated revertants multiply in histidine-free media. Since many carcinogens are converted to active forms by metabolism in the liver, preliminary incubation with liver homogenates may precede the bacterial assay. Essentially all chemicals known as carcinogens in humans cause mutagenesis in the Ames test. The other options—carcinogenicity screening in immunosuppressed (nude) mice, computer modeling, or incubation with mammalian cell cultures—may provide some information, but are less efficient and validated than the Ames test. Contamination of Michigan cattle feed with polychlorinated biphenyls (PCBs) did occur through an industrial mistake. 8-35. The answer is c. (Braunwald, pp 2469–2472.) This woman likely has myasthenia gravis; the incidence in women peaks in their twenties and thirties and women are more often affected, about 3:2, than men. Measurement of the antibody antiacetylcholine receptor provides a definitive diagnosis in 90% of cases of generalized disease, which this patient manifests, and 50% in ocular disease alone. Single-fiber electromyography is not
  • Block 8 Answers 321 specific for myasthenia gravis. Edrophonium chloride test, if unequivocally positive, makes the diagnosis highly probable. CT scan, MRI scan, and the EEG do not play a role in the diagnosis of myasthenia gravis. 8-36. The answer is a. (Hardman, p 338. Katzung, pp 438–439.) Ester-type local anesthetics are mainly hydrolyzed by pseudocholinesterases. Amidetype local anesthetics are hydrolyzed by microsomal enzymes in the liver. Of the listed agents, only lidocaine is an amide and can be influenced by liver dysfunction. 8-37. The answer is d. (Ryan, pp 550–555.) A male patient with the presentation as outlined (fatigue, weight loss, and lymphadenopathy) must be tested for antibodies to HIV. While other antibody tests may be relevant after the primary diagnosis, they must be considered after HIV is ruled out. Certainly, infectious mononucleosis is a possibility, but its occurrence in this age group is not as frequent as HIV. Patients are tested first by an ELISA screening test. If this test is positive (X2), then a confirmatory Western blot is performed. A Western blot separates the immune response into antibody production for specific components of the virus, that is, envelope, gag, and so forth. The following table shows the various bands that could be seen on a widely used Western blot and their identification by specific antigen source. There are at least three schemes for interpreting Western blots. Assuming technical competence in the laboratory, one of the more common reasons for falsely positive ELISAs and Western blots is an influenza vaccination within the past few months. A rare patient may have antibody to the cell line used to grow virus. Unlike Lyme disease, there is no reported crossreactivity with Epstein-Barr virus (EBV) or HTLV. There appears to be no naturally occurring antibody to retroviruses. Antigen Source gp 160 gp 120 gp 41 gp 31 gp 51 p 66 p 24 env gene product env fragment transmembrane fragment pol gene product core protein (gag) Abbreviations: gp, glycoprotein; p, protein; env, envelope; pol, polymerase.
  • 322 Clinical Vignettes for the USMLE Step 1 8-38. The answer is d. (Cotran, pp 1275–1276.) Inflammatory polyneuropathies may be acute or chronic. Acute inflammatory demyelinating polyradiculoneuropathy (Guillain-Barré syndrome) is a life-threatening disease of the peripheral nervous system. The disease usually follows recovery from an influenza-like upper respiratory tract infection and is characterized by a motor neuropathy that leads to an ascending paralysis that begins with weakness in the distal extremities and rapidly involves proximal muscles. Sensory changes are usually minimal. The disease is thought to result from immune-mediated segmental demyelination. In rare patients, instead of an acute course, Guillain-Barré syndrome takes a chronic course with remissions and relapses. This process is called chronic inflammatory demyelinating polyradiculoneuropathy (CIDP). 8-39. The answer is d. ( Junqueira, pp 385–386, 393, 395. Moore, Developing Human, p 320.) The newborn described is genotypically female and suffers from adrenogenital or congenital virilizing hyperplasia in which there is a deficiency in the pathway that leads to cortisol synthesis. The inability to synthesize cortisol in turn leads to production of high levels of ACTH and ACTH-releasing factor from the hypothalamus. The result is hypertrophy of the fetal adrenal cortex, which is a critical fetal structure that produces dehydroepiandrosterone. The excessive production of androgens by the fetal adrenal leads to masculinization of the female genitalia. Increased secretion of cortisol cannot occur because of the metabolic defect in this pathway; therefore, negative feedback control is not functional. The fetal cortex is part of maternal-feto-placental unit because the dehydroepiandrosterone is used by the placenta to produce estradiol. The fetal adrenal cortex involutes following birth, causing an overall reduction in the size of the adrenal. The adult cortex (zona glomerulosa, zona fasciculata, and zona reticularis) replaces the fetal adrenal cortex. The zona fasciculata and zona reticularis produce androgens after birth. Vasopressin [AVP; also known as antidiuretic hormone (ADH)] is released by the posterior pituitary and regulates fluid balance. ADH increases the permeability of the collecting duct through an aquaporin-mediated mechanism. Androgen insensitivity is the cause of testicular feminization and is not a factor in the adrenogenital syndrome. 8-40. The answer is e. (Conger, pp 337–339.) The nature of an adolescent boy’s relationship with his parents is the single factor most predictive of
  • Block 8 Answers 323 juvenile delinquency. In the most extensive study of the subject, J. G. Bachman found that the better a boy reported he got along with his parents, the less likely he was to engage in delinquent behavior. Other studies have found that delinquency is related to overly severe punishment and overly lax home disciplines as well as to an atmosphere of mutual hostility and rejection between parents and children. Despite the widely held belief that most delinquents come from broken homes, recent evidence indicates that the incidence of delinquency among boys of unhappy, though intact, homes is greater than that among boys of broken homes. Gerald Patterson has identified four “lacks” in the family interactions of delinquents: lack of house rules, lack of parental monitoring of behavior, lack of effective contingencies resulting in inconsistent responses to unacceptable behavior, and lack of effective ways of dealing with family crises that lead to tension and unresolved disputes. 8-41. The answer is a. (Braunwald, p 1982.) Transsphenoidal surgery has the advantages of potential cure with rapid therapeutic response. If the tumor is completely resected, the patient may experience a complete cure. Medical therapy with somatostatin agonist or bromocriptine is helpful, but the patient is dependent on medical therapy indefinitely. Irradiation takes years for full effectiveness and the patient may develop hypopituitarism. Transfrontal surgery is rarely used now. 8-42. The answer is b. (Katzung, pp 727–728.) Metformin is contraindicated in patients with type II diabetes in a number of instances, including renal disease, liver disease, chronic cardiopulmonary dysfunction leading to hypoxia, and alcoholism. 8-43. The answer is d. (Simon, pp 138–145.) From the lateral geniculate nucleus, there are two trajectories that the fiber pathways take en route to the visual cortex. One pathway passes dorsally through the parietal lobe and terminates in the upper bank of the calcarine fissure in the ipsilateral primary visual cortex. The second pathway takes a more circuitous (ventral) route—called the Meyer-Archambault loop—through the temporal lobe and terminates in the lower bank of the calcarine fissure in the ipsilateral primary visual cortex. The lower bank of the calcarine fissure is associated with the upper visual quadrants of the contralateral visual fields for both eyes, while the upper bank of the calcarine fissure is associated with the
  • 324 Clinical Vignettes for the USMLE Step 1 lower quadrants of the contralateral visual fields for both eyes. Thus, if there is a lesion of the left temporal lobe affecting the Meyer-Archambault loop, then the right upper quadrant for each eye will be affected. This deficit is referred to as a right upper quadrantanopia. 8-44. The answer is d. (Hardman, pp 4–9. Katzung, pp 41–43.) Bioavailability is defined as the fraction or percentage of a drug that becomes available to the systemic circulation following administration by any route. This takes into consideration that not all of an orally administered drug is absorbed and that a drug can be removed from the plasma and biotransformed by the liver during its initial passage through the portal circulation. A bioavailability of 25% indicates that only 20 mg of the 80-mg dose (i.e., 80 mg × 0.25 = 20 mg) reached the systemic circulation. Organ clearance can be determined by knowing the blood flow through the organ (Q) and the extraction ratio (ER) for the drug by the organ, according to the equation CLorgan = Q × ER The extraction ratio is dependent upon the amounts of drug entering (Ci) and exiting (Co) the organ: Ci × Co ER = ᎏ Ci In this problem, the amount of verapamil entering the liver was 76 mg (80 mg × 0.95) and the amount leaving was 20 mg. Therefore, 76 mg − 20 mg ER = ᎏᎏ = 0.74 76 mg CLliver = (1500 mL/min) (0.74) = 1110 mL/min 8-45. The answer is e. (Ryan, pp 282–283.) Enterococci causes a wide variety of infections ranging from less serious, for example, urinary tract infections, to very serious, such as septicemia. A Gram-positive coccus resistant to penicillin must be assumed to be enterococcus until other more definitive biochemical testing places the isolate in one of the more esoteric groups of Gram-positive cocci. Once isolated, there are a variety of tests to speciate enterococci. However, penicillin-resistant, non-β-lactamase-
  • Block 8 Answers 325 producing, vancomycin-resistant, Gram-positive cocci are most likely Enterococcus faecium. There are a variety of mechanisms for vancomycin resistance in E. faecium and they have been termed Van A, B, or C. These isolates have become one of the most feared nosocomial pathogens in the hospital environment. Unfortunately, no approved antibiotics can successfully treat vancomycin-resistant enterococci (VRE), only some experimental antibiotics such as Synercid. 8-46. The answer is b. (Afifi, pp 513–521.) The symptoms described are characteristic of hydrocephalus. Hydrocephalus may come about as a result of defects such as the failure of formation of the cerebellar vermis, foramens of Magendie and Luschka, or of the corpus callosum. There is an enlarged cranium as a result of the buildup of cerebrospinal fluid (CSF), causing brain damage. Several of the symptoms may also be caused by a compression of the posterior fossa and the absence of a cerebellar vermis. Cleft palate is a fissure of the medial aspect of the lip and would not result in the symptoms described previously. Anencephaly is the complete or partial absence of the brain and is not compatible with life. Syringomyelia is associated with bilateral segmental loss of pain and temperature. A congenital aneurysm can occur in a variety of places within the CNS and is typically associated with stroke in the adult. 8-47. The answer is d. (Cotran, pp 869, 875–876. Chandrasoma, pp 655–658.) Reye’s syndrome (RS) is an acute postviral illness that is seen mainly in children. It is characterized by encephalopathy, microvesicular fatty change of the liver, and widespread mitochondrial injury. Electron microscopy (EM) reveals large budding or branching mitochondria. The mitochondrial injury results in decreased activity of the citric acid cycle and urea cycle and defective β-oxidation of fats, which then leads to the accumulation of serum fatty acids. The typical patient presents several days after a viral illness with pernicious vomiting. RS is associated with hyperammonemia, elevated serum free fatty acids, and salicylate (aspirin) ingestion. In contrast, Wilson’s disease, which is related to excess copper deposition within the liver and basal ganglia of the brain, is characterized by varying liver disease and neurologic symptoms. The liver changes vary from fatty change to jaundice to cirrhosis, while the neurologic symptoms consist of a Parkinson-like movement disorder and behavioral abnormalities. A
  • 326 Clinical Vignettes for the USMLE Step 1 liver biopsy may reveal steatosis, Mallory bodies, necrotic hepatocytes, or cholestasis. Increased copper can be demonstrated histologically using the rhodamine stain. α1 antitrypsin deficiency causes both liver disease and lung disease, especially panacinar emphysema. Liver biopsies reveal red blobs within the cytoplasm of hepatocytes that are PAS-positive and diastase-resistant. Dubin-Johnson syndrome is associated with conjugated hyperbilirubinemia that results from decreased hepatic excretion of conjugates of bilirubin. 8-48. The answer is b. (Rhoades, p 38.) Periodic hyperkalemic paralysis is caused by inactivation of the skeletal muscle membranes. Inactivation is produced by depolarization of the skeletal muscle membrane, which occurs when extracellular potassium concentration increases. Inactivation of the sodium channels on the skeletal muscle membrane prevents action potentials from being produced and therefore leads to muscle weakness or paralysis. Although the exact mechanism of periodic hyperkalemic paralysis is not known, it appears to be due to a mutation in the gene coding for the sodium inactivation gate. 8-49. The answer is a. (Nolte, pp 485–492.) The classic appearance of a patient with a lesion of the cerebellar hemispheres is one in which voluntary and skilled movements are affected. They are uncoordinated and there are errors in the range, force, and direction of movement. The relationships between the cerebellum and the motor regions of the cerebral cortex have been disrupted. Lesions of other regions such as the flocculonodular lobe, vermal region of the anterior cerebellar cortex, or fastigial nucleus produce different symptoms (disturbances of balance, muscle tone, or nystagmus). Although pure lesions limited to the ventral spinocerebellar tract have not been reported, it is likely that such a lesion could not account for the symptoms indicated in this question. Information carried by this tract concerns activity of Golgi tendon organs of muscles of the lower limbs. 8-50. The answer is c. (Damjanov, pp 886–887, 928–930. Duchin, pp 949–955.) The Hantavirus genus belongs to the Bunyaviridae family and includes the causative agent of a group of diseases that occur throughout Europe and Asia and are referred to as hemorrhagic fever with renal syndrome. The characteristic features of this syndrome are hematologic abnormalities, renal involvement, and increased vascular permeability.
  • Block 8 Answers 327 Respiratory involvement is generally minimal in these diseases. Although several species of rodents in the United States are known to be infected with Hantavirus, no human cases were reported until an outbreak of severe, often fatal respiratory illness occurred in the United States in May 1993 in the Four Corners area of New Mexico, Arizona, Colorado, and Utah. This illness resulted from a new member of the genus Hantavirus that caused a severe disease characterized by a prodromal fever, myalgia, pulmonary edema, and hypotension. The main distinguishing feature of this illness, which is called Hantavirus pulmonary syndrome, is noncardiogenic pulmonary edema resulting from increased permeability of the pulmonary capillaries. Laboratory features common to both Hantavirus pulmonary syndrome and hemorrhagic fever with renal syndrome include leukocytosis, atypical lymphocytes, thrombocytopenia, coagulopathy, and decreased serum protein concentrations. Abdominal pain, which can mimic an acute abdomen, may be found in both Hantavirus pulmonary syndrome and hemorrhagic fever with renal syndrome. Dengue fever virus is a type of flavivirus; flaviviruses which are similar to alphaviruses. Dengue fever (breakbone fever) is initially similar to influenza but then progresses to a rash, muscle pain, joint pain, and bone pain. It can produce a potentially fatal hemorrhagic disorder. Yellow fever virus, which causes yellow fever, is another flavivirus. It is spread by a mosquito and produces characteristic coagulative necrosis of liver acinar zone 2 (midzonal necrosis). The necrotic hepatocytes produced by the process of apoptosis in the absence of inflammation result in Councilman bodies. Because of liver failure, patients become jaundiced (hence the term yellow fever) and may vomit clotted blood (“black vomit”). Another flavivirus is the cause of St. Louis encephalitis, which is spread by the Culex mosquito. Alphaviruses, a type of togavirus, are similar to flaviviruses. They are the prototypical arboviruses, which are arthropod-born viruses. Clinical diseases include eastern equine encephalitis (EEE), western equine encephalitis (WEE), and Venezuelan equine encephalitis (VEE). Ebola virus is a member of the Filoviridae family that causes a severe hemorrhagic fever. Outbreaks occur in Africa and typically make the national news.
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  • 330 Bibliography Greenspan FS, Gardner DG: Basic & Clinical Endocrinology, 6/e. New York, McGraw-Hill, 2001. Guyton AC, Hall JE: Textbook of Medical Physiology, 10/e. Philadelphia, Saunders, 2000. Hardman JG, Limbird LE (eds): Goodman & Gilman’s the Pharmacological Basis of Therapeutics, 9/e. New York, McGraw-Hill, 1996. Hazzard WR, et al (eds): Principles of Geriatric Medicine and Gerontology, 4/e. New York, McGraw-Hill, 1999. Henry JB, et al (eds): Clinical Diagnosis and Management by Laboratory Methods, 19/e. Philadelphia, Saunders, 1996. Howard BJ, Keiser JF Smith TF Weissfeld AS, Tilton RC: Clinical and Path, , ogenic Microbiology, 2/e, St. Louis, Mosby, 1993. Hughes M, Kroehler CJ, Vander Zanden JW: Sociology: The Core, 5/e. New York, McGraw-Hill, 1999. Junqueira LC, Carneiro J, Kelley RO: Basic Histology, 9/e. Stamford, CT, Appleton & Lange, 1998. Kandel ER, Schwartz JH, Jessel TM: Principles of Neural Science, 4/e. New York, McGraw-Hill, 2000. Kaplan HL, Sadock BJ: Synopsis of Psychiatry, 8/e. Baltimore, Williams & Wilkins, 1998. Katzung BG: Basic and Clinical Pharmacology, 8/e. New York, McGraw-Hill, 2001. Kingsley RE: Concise Text of Neuroscience, 2/e. Philadelphia, Lippincott, Williams & Wilkins, 2000. Kumar, V, Cotran RS, Robbins SL. Basic Pathology, 6/e. Philadelphia, Saunders, 1997. Levinson W, Jawetz E: Medical Microbiology & Immunology, 6/e, New York, McGraw-Hill, 2000. Martin JH: Neuroanatomy, 2/e, Stamford, CT, Appleton & Lange, 1996. McKenzie, JC, Klein RM: Basic Concepts in Cell Biology and Histology. New York, McGraw-Hill, 2000. McPhee SJ, Lingappa VR, Ganong WF Lange JD (eds): Pathophysiology of , Disease, 2/e. Stamford, Connecticut, Appleton & Lange, 1997. Moore KL, Persaud TVN: Before We Are Born, 5/e. Philadelphia, Saunders, 1998. Moore KL, Persaud TVN: The Developing Human, 6/e. Philadelphia, Saunders, 1998.
  • Bibliography 331 Moore KL, Dalley AF: Clinically Oriented Anatomy, 4/e. Baltimore, Lippincott, Williams & Wilkins, 1999. Murray RK, Granner DK, Mayes PA, Rodwell, VW: Harper’s Biochemistry, 25/e. New York, McGraw-Hill, 2000. Murray PR, Rosenthal KS, Kobayashi GS, Pfaller MA: Medical Microbiology, 5/e. St. Louis, Mosby, 1997. Noback CR, Strominger NL, and Demarest RJ: The Human Nervous System, 4/e. Philadelphia, Lea & Febiger, 1991. Nolte J: The Human Brain: An Introduction to Its Functional Anatomy, 4/e. St. Louis, MO, Mosby, 1999. Plomin R, DeFries JJ, McClearn GE, Rutter M: Behavioral Genetics: A Primer, 3/e. New York, WH Freeman, 1997. Purves D, Augustine GJ, Fitzpatrick D, Katz LC, LaMantia A-S, McNamara JO, Williams SM: Neuroscience, 2/e. Sunderland, Sinauer Associates, Inc., 2001. Raoult D, Tilton RC: Dictionary of Infectious Diseases, Elsevier, New York, 2000. Rhoades RA, Tanner GA: Medical Physiology. Boston, Little, Brown and Company, 1995. Rubin E, Farber JL: Pathology, 3/e. Philadelphia, Lippincott, 1999. Ryan KT (ed): Sherris’s Medical Microbiology, 3/e, Appleton & Lange, Stamford, CT, 1994. Sack GH Jr: Medical Genetics. New York, McGraw-Hill, 1999. Scriver CR, Beaudet AL, Sly WS, Valle D: The Metabolic and Molecular Bases of Inherited Disease, 7/e. New York, McGraw-Hill, 1995. Siegel GJ, Agranoff BW, Albers RW, Fisher SK, Uhler MD: Basic Neurochemistry, 6/e. Philadelphia, Lippincott, Williams & Wilkins, 1999. Sierles FS (ed): Behavioral Science for Medical Students, Baltimore, Williams & Wilkins, 1993. Simon RP, Aminoff MJ, Greenberg DA: Clinical Neurology, 4/e. New York, McGraw-Hill, 1999. Sweeney L: Basic Concepts in Embryology: A Student’s Survival Guide. New York, McGraw-Hill, 1998. Taylor SE: Health Psychology, New York, McGraw-Hill, 1995. Waxman SG: Correlative Neuroanatomy, 24/e. New York, McGraw-Hill, 2000. Wedding D: Behavior and Medicine, 2/e. St. Louis, Mosby-Year Book, 1995. Wilson GN: Clinical Genetics: A Short Course. New York, Wiley-Liss, 2000.
  • 332 Bibliography Yen SSC, Jaffe RB, Barbieri RL: Reproductive Endocrinology, 4/e. Philadelphia, Saunders, 1991. Young B, Heath JW: Wheater’s Functional Histology, 4/e. New York, Churchill Livingstone, 2000. Many genetic diseases cited in this book include a six-digit McKusick number that allows reference to the compendium of genetic diseases that is available in hard copy or online. This compendium is now maintained by the National Institutes of Health and lists more than 4000 genetic diseases and genetic loci. For all but the most recently entered disorders, the McKusick number provides the inheritance mechanism. Those numbers beginning with 1 designate autosomal dominant diseases, those beginning with 2 autosomal recessive diseases, those beginning with 3 X-linked recessive diseases, those beginning with 4 Y-linked diseases (so far only gene loci), and those beginning with 5 mitochondrial DNA–encoded diseases.
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