Lecture on hypothyroidism Internal Medicine UTHSCSA Esteban Toro Velez, MD Internal Medicine resident, PGY-2 2022

1. Hypothyroidism
Esteban Toro Velez
Internal Medicine, PGY-2
UTHSCSA

2. Outline
1. Background / Epidemiology
2. Screening
3. Types
4. Manifestations and Diagnosis
5. Treatment

3. Epidemiology and Background
● More prevalent in women, elderly
● Clinical/overt, subclinical
● Prevalence USA, Europe, Japan
○ 0.6-12 per 1000 women
○ 1.3 - 4.0 per 1000 in men
Almandoz J, Gharib H. Hypothyroidism: Etiology, Diagnosis, and Management. Medical Clinics of North America. 2012;96(2):203-221.
● Inadequate production of thyroid hormone
or inadequate action of thyroid hormone in
target
● Seen in outpatient practice
● Effect on metabolism and dysfunction in
multiple organ systems

5. Clinical manifestations
● Dry skin 76%
● Cold intolerance 64%
● Coarse skin 60%
● Puffy eyelids 60%
● Decreased eating 54%
● Weight gain 54%
● Paresthesias 52%
● Cold skin 50%
● Constipation 48%
● Dry skin
● Hair loss
● Puffy eyelids
● Hoarseness
● Slow movements.
● Delayed relaxation phase of
the deep tendon reflexes,
● Myoedema
● Goiter
● Thyroidectomy scar
● Hyponatremia
● Macrocytic anemia
● Elevated creatinine kinase
● Hyperlipidemia
● OSA
Patient complaints Physical exam Laboratory findings
McDermott M. Hypothyroidism. Annals of Internal Medicine. 2020;173(1):ITC1-ITC16.

6. Types
● Overt: TSH is elevated, with low free
and total T4.
● Prevalence 0.3-3.7%
● Subclinical: TSH is elevated but WNL,
T4 is normal
● Chronic lymphocytic thyroiditis
(Hashimoto thyroiditis), radioiodine
ablation, thyroidectomy, high-dose
head and neck radiation therapy.
Endemic iodine deficiency is the most
common cause worldwide.
● Conditions that affect the
hypothalamic or pituitary
disorders. Impairing thyrotropin
releasing hormone or TSH
production.
● Tumors surgery, radiation,
hemorrhage, infections,
infiltrative disorders, TBI,
medications
● Amyloidosis
● Hemochromatosis
● Medications
Primary Hypothyroidism Central and Secondary
1. McDermott M. Hypothyroidism. Annals of Internal Medicine. 2020;173(1):ITC1-ITC16.
Other

7. Screening
● TSH is the best test, as 99% is primary
● TSH is the first abnormality noted
● If central is suspected: Free T4 is ordered
● General screening is not recommended
● Recommendations for pregnant women
1. McDermott M. Hypothyroidism. Annals of Internal Medicine. 2020;173(1):ITC1-ITC16.

8. Diagnosis
● Physical exam: Nonspecific, subtle or absent
● Laboratory abnormalities: Suggestive but not diagnostic
● TSH, logarithmic relationship between fT4
● TSH increases with age (age adjusted)
● Usually, no need for T3 levels
● anti-tPO antibodies and antithyroglobulin antibodies-Hashimoto
○ Not recommended by ATA and AACE, as the cause of hypothyroidism is Hashimoto
○ Could be used to demonstrate autoimmune phenomena
● Ultrasound is not recommended, unless 1 or more nodules are identified
1. McDermott M. Hypothyroidism. Annals of Internal Medicine. 2020;173(1):ITC1-ITC16.

9. Central Hypothyroidism
● Low free T4, in association with low or normal TSH
● Known or high suspicion for hypothalamic disease
● T3 can be used to differentiate between hypothyroidism and nonthyroidal illness
○ T3 and reverse T3 (RT3)
○ Thyroid illness: TSH is low, T4 proportionally lower to T3 and RT3 are low
○ Non Thyroid Illness: T3 levels proportionally lower to T4, but elevated RT3
1. McDermott M. Hypothyroidism. Annals of Internal Medicine. 2020;173(1):ITC1-ITC16.

10. Recovery or Euthyroid Sick Syndrome
● TSH may be elevated in patients recovering from acute illness
● TSH should be rechecked in 6-8 weeks
● TSH secreting tumors, or resistance to TSH is rare
● Biotin supplements can affect TSH and free T4 assays
● Avoid wrong diagnosis of hypothyroidism
1. McDermott M. Hypothyroidism. Annals of Internal Medicine. 2020;173(1):ITC1-ITC16.

11. Subclinical Hypothyroidism
● Elevated TSH with normal total T4 or free T4 in adequate range
● Indicating that the T4 in that person is lower than it should be
● TSH increase to compensate
● Progress to overt in 2-6%
○ Higher if antibodies are present
1. McDermott M. Hypothyroidism. Annals of Internal Medicine. 2020;173(1):ITC1-ITC16.

13. Buttner E. Hypothyroidism [Internet]. Life in the Fast Lane • LITFL. 2022 [cited 10 October 2022]. Available from: https://litfl.com/hypothyroidism-ecg-library/

14. Buttner E. Hypothyroidism [Internet]. Life in the Fast Lane • LITFL. 2022 [cited 10 October 2022]. Available from: https://litfl.com/hypothyroidism-ecg-library/

21. Myxedema
● Hospitalization is mandatory for management of myxedema coma and may also be considered
for patients with severe hypothyroidism
● Most often in elderly patients
● Superimposed precipitating event
○ Cold exposure, infection, trauma, surgery, myocardial infarction, heart failure,
pulmonary embolism, stroke, respiratory failure, gastrointestinal bleeding, and use of
drugs that suppress the central nervous system
● Mortality rate 100% if untreated

25. Treatment
● Levothyroxine
● Absorbed in duodenum, converted peripherally
to T3
● 1.6 mcg/Kg (Lean body mass of 24-25Kg/m2)
● Check TSH in 6-8 weeks,
● Titrate by 12.5-25mcg/kg
● Older than 60 or with CAD, start at a low dose
25-50 mcg/kg
● Water 1 hour or 4 hours after meals
○ 4 hours from iron, calcium or soy
supplements
1. McDermott M. Hypothyroidism. Annals of Internal Medicine. 2020;173(1):ITC1-ITC16.

29. A 35-year-old woman is evaluated for a 2-month history of fatigue, cold intolerance, constipation, and menorrhagia. She has no recent
history of iodinated contrast or iodine supplementation. She takes no medications.
On physical examination, other than a pulse rate of 56/min, vital signs are normal. BMI is 22.
The thyroid is firm and diffusely enlarged two times the normal size. Also noted are dry cool skin and dry coarse hair. No thyroid
nodules are palpated.
Laboratory studies show a thyroid-stimulating hormone level of 12 μU/mL (12
mU/L).
Which of the following is the most appropriate next diagnostic test?
A. Free thyroxine measurement
B. Free triiodothyronine measurement
C. Thyroid peroxidase antibody titer
D. Thyroid ultrasonography

30. A 76-year-old woman is reevaluated after results of thyroid function tests performed 2 weeks ago are abnormal. The patient otherwise feels well. She
has a history of hypertension, atrial fibrillation, gastroesophageal reflux disease, and depression. Current medications are metoprolol, amiodarone,
warfarin, omeprazole, and sertraline.
On physical examination, blood pressure is 125/65 mm Hg, pulse rate is 83/min, and respiration rate is 15/min. The thyroid gland is smooth and of
normal size. Cardiac examination reveals an irregularly irregular rhythm. Deep tendon reflexes are normal.
Laboratory studies:
Thyroid-stimulating hormone: 6.5 µU/mL (6.5 mU/L)
Thyroxine (T4), free 2.4 ng/dL (31.0 pmol/L)
Triiodothyronine (T3), free 0.8 ng/L (1.2 pmol/L)
Which of the following medications is most likely responsible for the laboratory results?
A) Amiodarone
B) Metoprolol
C) Omeprazole
D) Sertraline