Hypothyroidism

Background

1. Affects ~4% US
2. 3-10x more common in F
3. Peak incidence at age >60
4. More common among Caucasians, Latinos than AA

Types

1. Primary: failure of thyroid
   1. elevated TSH, low FT4
2. Secondary: failure of pituitary
   1. low TSH, low FT4
3. Tertiary: failure of hypothalamus

Etiology

1. Primary
   1. Autoimmune
   2. Idiopathic
   3. Postsurgical thyroidectomy
   4. External radiation therapy
   5. Radioiodine therapy
   6. Inherited enzymatic defect
   7. Iodine deficiency
   8. Antithyroid drugs
   9. Lithium, phyenylbutazone
2. Secondary
   1. Pituitary tumor
   2. Infiltrative Dz (eg Sarcoid)

DDx

1. Addisons disease
2. anovulation
3. autoimmune thyroid disease
4. chronic fatigue syndrome
5. craniopharyngiomas
6. De Qeurvain Thyroiditis
7. Depression
8. Esoinophilia
9. euthyroid sick syndrome
10. fibromyalgia
11. goiter
12. hypochondriasis
13. hypopituitarism
14. hypothermia
15. infectious mononucleosis
16. iodine deficiency
17. lithium nephropathy
18. lymphoma
19. ovarian insufficiency
20. myxedema
21. pituitary macroadenoma
22. Prolactin deficiency
23. SIADH
24. thyroiditis

Work-Up

1. TSH
2. Total and Free T4
3. T3
4. Thyroid Binding Globulin (TBG)
5. auto-antibodies (anti-TPO, anti-microsomal, anti-Tg)
6. Ultrasound to look for nodules

Complications

Myxedema Coma

Treatment

1. Depends on etiology, consider starting Levothyroxine daily but be aware that doses too high may lead to thyroid storm
2. see Myxedema Coma

Disposition

1. most hypothyroidism is treated as an outpatient followed in ambulatory clinic
2. admit and treat sever hypothyroidism or myxedema coma

See Also

Endo: Myxedema Coma

Endo: Thyroid (General)

Source

Emedicine

Adapted from DeBonis