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USMLE – Hypothyroidism

Pathophysiology
1. Inadequate thyroid functioning
2. Iodine insufficiency
3. Autoimmune (Hashimoto’s disease)
4. Sequelae of hyperthyroidism treatment
5. Lithium
6. Alpha-interferon
7. Excess iodine administration (large contrast dye loads)
8. Amyloidosis
9. Sarcoidosis
10. Scleroderma
11. Hypopituitarism
12. Hypothalamic disorders
13. Bevarotene
14. Cretinism; the devastating sequelae have largely been eliminated in developed countries through intensive screening programs

Signs and Symptoms
1. Depression
2. Poor memory
3. Difficulty conentrating
4. Hypothermia
5. Cold hands and feet
6. Bradycardia
7. Weakness
8. Fatigue
9. Weight gain
10. Constipation
11. Puffy eyes, face and hands
12. Pretibial myxedema
13. Amenorrhea
14. Hearing loss
15. Delayed tendon reflexes
16. Muscle stiffness, pain, and cramps
17. Hypertrophy of proximal muscles
18. Galactorrhea
19. Hypothermia
20. Decreased blood pressure
21. Decreased stroke volume
22. Distant heart sounds
23. Mental retardation
24. Hypotonia
25. Enlarged tongue
26. Short stature
27. Muscle hypertrophy (“infant Hercules”)

Characteristic Test Findings
1. Increased TSH (in primary causes)
2. Decreased TSH (in secondary causes)
3. Low or low normal T4
4. Hyponatremia
5. Mild anemia
6. Increased cholesterol
7. Increased triglycerides
8. Increased serum phosphate
9. Increased serum CK
10. EKG – low voltage
11. Prolonged QT interval
12. Cardiomegaly (“water-bottle heart”) on chest radiograph

Associated Conditions
1. Increased incidence with – scleroderma, Addison’s disease, Waldenstrom’s macroglobulinemia
2. Increased incidence of – atherosclerotic coronary artery disease

Inheritance/Epidemiology
1. Most common cause worldwide is iodine deficiency
2. Most common cause in developed nations is autoimmune
3. 5 times more common in women

Treatment
1. Removal or treatment of underlying cause, if known
2. Exogenous T4 (levothyroxine) or T3/T4 compounds (may require up to 6 months for return to clinical and laboratory baseline)

Tips for the USMLE
1. If tibial area has pitting edema, it is not hypothyroidism (pretibial myxedema is nonpitting)
2. If a 38-year-old woman has a gradual loss of energy, weight gain over several months, difficulty concentrating, loss of the outer part of her eye-brows, pully eyelids, and a feeling of coldness in her hands, think hypothyroidism

Lillian Thompson By Lillian Thompson

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