Diagnosis of cns infections


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Diagnosis of cns infections

  1. 1. CNS infections  Meningitis,  Encephalitis,  Parameningeal abscesses (subdural empyema and epidural abscess),  Brain abscesses, &  CSF shunt infections.
  2. 2. Meningitis • is an inflammatory response to bacterial infection of the pia-arachnoid and CSF of the subarachnoid space
  3. 3. Epidemiology  Incidence is between 3-5 per 100,000  More than 2,000 deaths annually in the U.S.
  4. 4. • Bacterial meningitis and other CNS infections are considered infectious disease emergencies that can cause significant patient morbidity and mortality.
  5. 5. Mortality/Morbidity  Bacterial meningitis -uniformly fatal before the antimicrobial era.  overall mortality rate has decreased, but remains alarmingly high - - Higher in developing countries  Varies with the specific etiologic agent     S pneumoniae 19-26% H influenzae - 3-6% N meningitidis 3-13%, L monocytogenes 15-29%
  6. 6. `  Survivors end up with complications  Children suffers mostly with complications
  7. 7. Morbidity associated with complications in children In adults sensorineural hearing loss / Cranial nerve palsies brain infarction,, epilepsy hydrocephalus, diffuse brain swelling hydrocephalus, cerebral vein thrombosis, cerebral palsy More with H.influenzae meningitis **** Severe morbidity is associated with H.influenzae meningitis and TB meningitis due to fibrinous exudates
  8. 8. Viral meningitis  Viral meningitis (without encephalitis) is less than 1%.  In patients with deficient humoral immunity (eg, agammaglobulinemia), enterovirus meningitis may have a fatal outcome.
  9. 9. Meningococcal Meningitis belt - Faso, Chad, Ethiopia and Niger; in 2002, the outbreaks occurring in Burkina Faso, Ethiopia and Niger accounted for about 65% of cases
  10. 10. Pathogenesis of Meningitis Survival and Multiplication in the subarachnoid space Nasopharyngeal colonization Neisseria meningitides (meningococcus) and nasopharyngeal colonization with S pneumoniae (pneumococcus). Crossing of the BBB and entry into the CSF Nasopharyngeal epithelial cell invasion Bacteremia with intravascular survival Bloodstream invasion
  11. 11. Pathogenesis of Meningitis eg, Naegleria fowleri, Free living amoeba in natural resovoires Meningitis Nasopharyngeal epithelial cell invasion Retrograde flow to meninges through the olfactory bulb
  12. 12. Pathogenesis of Post traumatic/Neurosutgery Meningitis Colonizing bacteria in sinuses/auditory canal otitis media, congenital malformations, trauma, direct inoculation during intracranial manipulation Spread along the CSF fistulous tract Meningitis
  13. 13. Pathogenesis cont….  With in the CNS, the infectious agents likely survive as immunoglobulins, neutrophils, complement components absent or activity limited  replication of infectious agents remain uncontrolled triggers the cascade of meningeal inflammation  Increased CSF concentrations of TNF-alpha, IL-1, IL-6, and IL-8 are characteristic findings in patients with bacterial meningitis
  14. 14.  Treatment using rapidly bactericidal agents may transiently worsen the patients condition due to rapid release of pyrogenic substances in to CSF  Increase of proinflammatory mediators
  15. 15. Specific Pathogens
  16. 16. Age group Predominant Pathogen Age 0-4 weeks S agalactiae (group B streptococci) E coli K1 L monocytogenes Age 4-12 weeks S agalactiae E coli H influenzae S pneumoniae N meningitidis Age 3 months to 18 years N meningitidis (worldwide epidemic strains A,B,C W135) S .pneumoniae H influenzae Age 18-50 years S pneumoniae N meningitidis H influenzae Age older than 50 years S pneumoniae N meningitidis L monocytogenes Aerobic gram-negative bacilli Immunocompromised state S pneumoniae N meningitidis L monocytogenes Aerobic gram-negative bacilli
  17. 17. Intracranial manipulation, including neurosurgery Staphylococcus aureus Coagulase-negative staphylococci Aerobic gram-negative bacilli, including Pseudomonas aeruginosa Basilar skull fracture S pneumoniae H influenzae Group A streptococci CSF shunts Coagulase-negative staphylococci S aureus Aerobic gram-negative bacilli ***Direct extension from the throat or nasal or ear colonization an give rise to post traumatic meningitis
  18. 18. Other causes  Bacteraemic infectionof Salmonella, Brucella and      Staphylococcus aureus can cuase meningitis Gram Negative meningitis in overwhelming infections due to Strogyloides / Hyper infection due to Strongyloides stercorhalis Leptospira and Treponema Protozoa – Acanthomoeba and Naeglaria fowleri Fungi – Histoplasma and Nematodes – Angyostrogilus cantonensis
  19. 19.  Clinical diagnosis unreliable- symptoms unreliable – specially extremes of age  The efficacy of treatment (CNS) infections -depends on the accuracy of the etiologic diagnosis.  requires the best specimen at the appropriate time,  transporting it to the laboratory under optimum conditions,  processing the specimen efficiently and timely manner,  and selecting the tests necessary to identify the spectrum of possible etiologies
  20. 20. Clinical sign Kernig's sign sensitivity, 5%; likelihood ratio for a positive test result [LR(+)], 0.97) Brudzinski's sign (sensitivity, 5%; LR(+), 0.97), Nuchal rigidity (sensitivity, 30%; LR(+), 0.94) Degree of meningeal inflamation ≥ 6 up to 100 Clinical signs are unreliable Inbetween Unreliable (>/=1000 WBCs/mL of CSF Nuchal rigidity shows diagnostic value- sensitivity 100% and negative predictive value 100%
  21. 21. Diagnosis  Should not be delayed  Inform laboratory  Initial report based on Cell count and Direct smear  Cytospin method gives more positive yield than traditional overlaying  Gram stain can be considered as the gold standard
  22. 22. Diagnosis  Is established by investigation of CSF obtained from     lumbar puncture, Cysternal puncture or ventricular puncture or fontanelle taps possible – not done routinely Exclude raised intracranial pressure before performing the procedure due to possibility of herniation Place of CT/ MRI to exclude SOL When, contraindication +, diagnosis established using other means – Blood culture, WBC/DC, CRP together with symptoms
  23. 23. Additional factors for success  Communication between the clinician and laboratory- about clinical notes, Patient condition, antibiotic therapy, Patient delay and Doctor delay  Seasonal prevalence of infectious diseases, for enteroviruses and arboviruses,  the epidemiology of emerging diseases such as West Nile virus, and the immune status of the patient can beis helpful.
  24. 24. Specimen collection and transportation –timing  All specimens should be collected prior to the initiation of antimicrobials  If therapy initiated – action to nullify it-Innoculating it to broth media 1:5 ratio< specially for cerebral abcess
  25. 25. Specimens – for diagnosis of CNS infections Disease Specimen Meningitis Cerebrospi • Mininmum of 1 mL nal fluid /culture (CSF) • 1 to 2 mL [PCR]), • 1 mL antibody test Blood Encephalit is or brain abscess Quantity 5 to 10ml as for blood culture Note For M. tuberculosis, and dimorphic and filamentous fungi require repeat CSF or large volumes (10 to 20 mL) of ventricular CSF. 0.5 to 1.0 mL per culture request preferred 1 to 10 mL can be added to blood culture medium ↓antimicrobial effect- dilution of 1 :5 or 1:10 Tissue Subdural empyema or epidural Abscess material or irrigation fluid 0.5 cc preferred minced /gently ground. Mince only if filamentous fungi expected. Abscess material / irrigation 0.5–1.0 mL per culture request preferred Small volumes of pus diluted (ratio of 1:2) with sterile saline to allow “washing” of material from
  26. 26. Collection and transportation Specimen Container Transport/Storage Conditions Cerebrospinal fluid (CSF) Sterile tube. Room temperature. Ice/Refrigeration are detrimental to some bacteria and anaerobes. For PCR 4 °Cfor <24 hr or freezing (−20°C) for longer periods. Pus, irrigation fluid, and fluid aspirates Sterile container. Anaerobic culture request requires transport in oxygen-free container. Room temperature for short periods (<1 hr). Refrigeration for longer times. Do not refrigerate if anaerobic culture is ordered. Tissue, debridement material Sterile container. Keep small specimen portions moist with sterile saline solution. As for pus above. Small pieces of tissue can be placed on sterile moist gauze to facilitate location/identification by laboratory personnel. Portion for PCR as for CSF above. Abscess material, fluid, and washes aspirated Under anerobic conditions in to Nitrogen or CO₂ , Large volumes-To a syringe itself- short time Or pre reduced aneerobic Transport as soon as possible
  27. 27. Collection of CSF  Cerebrospinal fluid collected by lumbar puncture is the routine specimen for diagnosis of meningitis  Strict aseptic techniques  Three or four containers – depending on tests requested  But should have separate tubes for Gram stain/culture, Biochemistry and glucose level- accompanied by blood sample for RBS  Never to keep it in refrigerator
  28. 28. Which tube for microbiology?  Any tube possible  First tube- Theoretically risk of contamination - epithelium or blood from skin and soft tissue capillaries ruptured during the punctur  In practice, total volume of fluid is more important than the “tube” cultured.
  29. 29. CSF Examinations  Macroscopy – color,clotting etc  Complete count  Differential count  Gram stain of direct smear  Culture  Biochemistry – sugar difference and proteins  PCR when indicated
  30. 30. CSF Macroscopy
  31. 31. Color of CSF supernatant Conditions or causes Purulent Pyogenic meningitis Yellow Blood breakdown products Hyperbilirubinemia CSF protein >=150 mg per dL (1.5 g per L) >100,000 red blood cells per mm3 Orange Blood breakdown products High carotenoid ingestion Pink Blood breakdown products Green Hyperbilirubinemia Purulent CSF Brown Meningeal melanomatosis
  32. 32. Normal CSF values Cell component Age Category Normal Value Leukocytes Neonates 0 – 30 cells X 10 ⁶ / L 1 to 4 yr old 0 – 20 X 10⁶ / L 5 to puberty 0 – 10 X 10⁶ / L Newborn 0 – 675 X 10⁶ / L Adults 0 – 10 X 10⁶ / L Neonates 0.7 g/l Adults 0.2 – 0.4 g/l Erythrocytes Protein Glucose > 60% of RBS value is considered normal •Bacterial or viral counts should be considered where leukocyte counts are near the upper normal value •5 WBCs per mm3 (normal value)
  33. 33. differential diagnosis of various forms of meningitis Diagnosis Pressure Cells (10⁶ / l) PMN Glucose ratio Protein (g/ l) Lactate (mmol/l) normal < 20 cm 1-2 <1 > .5 < 0.45 (15– 45mg/dl) <2 Acute pyogenic >20 cm >1000 > 50% < .4 (>.2) > 1(100 mg) > 4 Chronic variable > 1000 Vary < .4 > 0.45 >2 Aseptic (Viral) < 20 cm < 1000 <50 > .4 Vary <2
  34. 34. 87% of Patients with meningitis ≥ 1000 /mm³ WBCs 99% of Patients with meningitis ≥100 per mm3 More likely to have viral meningitis ≤ 100 per mm3  As CSF is hypotonic, WBCs lyse with the time.  Process, immediately
  35. 35. Lymphocytes : PMN  CSF, PMN:L ratio is unreliable for diagnosis of meningitis  Viral meningitis may show lymphocytosis – but initially PMN predominates  Neutropaenics – no or less PMN response
  36. 36. Presence of RBC’s  Indicates intra cerebral ,SAH or traumatic tap  Presence of RBC’s make interpretation of CSF analysis     difficult But, rarely obscures it Inspecting first and third lumbar puncture samples – if RBC count different - Traumatic tap WBC:RBC ratio of 1:500 to 1:1000 is considered normal CSF obtain > 12 hrs post ICH may have WBC counts up to 500 X 10⁶ /l - due to inflammation
  37. 37. Direct smear – Gram stain
  38. 38.  a Gram stain of the cytospin CSF has a sensitivity of 90% if the LP is carried out before the administration of antibiotics.
  39. 39. Effects of antibiotics in CSF culture and Direct smears  In a retrospective review of 128 children with bacterial meningitis, Kanegaye et al. (2001)  compared 39 patients who received empiric antimicrobial therapy before LP with 55 who underwent LP before receiving antimicrobial therapy Treatment Group - Bacterial sterilization Treatment group Meningococcus – sterilization occurred within 2 hrs Up to 24 to 48 hrs CSF cellular and biocheical parameters remained unchained Pneumococcus – sterilization occurred within 4 hours
  40. 40. Condition Diagnostic test Bacterial meningitis Cytospin Gram stain 60–90 100 Culture 90 100 Antigen detection assays * 50–100 100 Acid-fast stain 10–22 100 38–88 100 27–85 95–100 Tuberculous meningitis Culture PCR Sensitivity (%) Specificity (%) Effect of antibiotic treatment on
  41. 41. Blood cultures • 50 to 80% patients with meningitis has accompanied bacteremias - blood cultures would be useful to isolation of organisms – more than CSF growth • Specially where LP is contraindicated Blood cultures Volume – 20ml or as recommended by the manufactures •Collected before antibiotic therapy •> 2 cultures taken from different sites or three cultures with in 24 hrs •Innoculate into broth medium at a ratio of >1:5 When suspecting – Dimorphic fungi or cryptococcus blod should be colected to tube containing lysis solution – for lysis centrifugation
  42. 42. Utility of Gram stain for diagnosis of Pyogenic meningitis Etiology Sensitivity All common etiologies—no previous antibiotics 75% to 90% All common etiologies—antimicrobial therapy prior to lumbar puncture 40% to 60% Streptococcus pneumoniae –without antibiotics 90% Neisseria meningitidis - 75% Haemophilus influenzae 86% Listeria monocytogenes <50%
  43. 43.  Unfortunately the positivity rate of gram staining and cultures remain low between 25- 40% as against the rate of 80-85% from the developed world
  44. 44. Partially treated meningitis  As the early symptoms and signs - non-specific, up to 50% receive oral antibiotics.  This delay the presentation to hospital & CSF findings altered; - Gram stain and growth of organism may be negative –  Antibiotics rarely interfere with CSF protein/glucose and molecular diagnosis (PCR).  In partially treated meningitis – request for PCR and bacterial antigens - not affected by prior antibiotic administration.
  45. 45. Tuberculuos meningitis  AFB positive only in 3%  Cobweb formation is seen 2/3 cases  Ratioo of albumin to globulin changes can be used as sxcrrening method(Nl ratio 6:1)Abnormal in TBM changes can be predicted with eletrophoresis (Modified Levinson’s test
  46. 46. Use of Bacterial Antigen Testing  The use of rapid bacterial antigen detection in CSF and other body fluids has come under question.  Rarely does a positive result alter therapy, and test performance is similar to that of the Gram's stain.  Two contemporary approaches are advocated for bacterial antigen testing.  The first recommends testing only those specimens with abnormal CSF parameters (cell count, protein, glucose).[35] This approach results in a 68% reduction in the number of antigen tests performed.  Although positive CSF cultures occur when white blood cell count, glucose, and protein values are within normal ranges, this is unusual and does not justify testing all CSF for bacterial antigen.  Another approach eliminates antigen testing, except in a few limited, specific cases, such as prior antimicrobial therapy when culture results are negative after 24 to 48 hours of incubation.
  47. 47.  latex particle agglutination tests , have similar sensitivities to Gram stain or culture  of doubtful benefit when used routinely,  but sometimes identify organisms in patients with partially treated bacterial meningitis and negative Gram stain and culture.  Cultures for bacteria and fungi should always be performed, even in patients already treated with antibiotics.
  48. 48.  Use of Culture
  49. 49. Culture media Incubation For routinely encountering pathogens Good quality Blood A, chocolate Agar either sheep or HBA - 24 to 48 hrs in 35% CO₂ Facultative anaerobes Broth media Anaerobes from cerebral abscesses thioglycollate or chopped Extended meat broth, incubation- only when requested Yeast and fungi Use of lysis centrifugation method Only when requested ********Culturing technique and media hardly ever changed over the years
  50. 50. Emerging issues
  51. 51.  Methods of rapid diagnosis  Emergence of antibiotic resistant Pathogens
  52. 52. PCR  Broad range of PCRs – N.meningitidis, H.influenzae,Streptococcus pneumoniae  PCR of blood Buffy coat provide higher yield for N. meningitidis  Agents of Aseptic meningitis –Rapid RealTime PCR for entero viruses available – results in 60 min
  53. 53. Antibiotic resistance  worldwide increase in infection with penicillin and     cephalosporin resistant strains of S pneumoniae, caused by either alteration in the penicillin binding proteins (Mosaic PBP) Incidence increasing Europe, South Africa, Asia, and the United States. American Academy of Pediatrics recommended combination therapy, initially with vancomycin and either cefotaxime or ceftriaxone for all children 1 month of age or older with definite or probable bacterial meningitis. N. meningitis less susceptible strains