Hypothyroidism

Background

1. 3-10x more common in F
2. Peak incidence age >60

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 (thyroid gland)
   1. Autoimmune (Hashimoto)
   2. Thyroiditis (subacute, silent, postpartum)
      1. Often preceded by hyperthyroid phase
   3. Iodine deficiency
   4. After ablation (surgical, radioiodine)
   5. After external radiation
   6. Infiltrative disease (lymphoma, sarcoid, amyloid, TB)
   7. Congenital
   8. Meds
      1. Amiodarone, Li, iodine, interferon, interleukin
   9. Idiopathic
2. Secondary (Hypothalamus-pituitary axis)
   1. Panhypopituitarism
   2. Pituitary adenoma
   3. Infiltrative causes (e.g., hemochromatosis, sarcoidosis)
   4. Tumors impinging on the hypothalamus
   5. History of brain irradiation
   6. Infection (e.g., tuberculosis)

Clinical Features

1. Constitutional
   1. Cold intolerance
   2. Wt gain
   3. Weakness
   4. Lethargy
   5. Hypothermia
   6. Hoarse voice
   7. Hair loss
   8. Constipation
   9. Dysfunctional uterine bleeding
2. Neuropsychiatric
   1. Delayed relaxation of DTRs
   2. Paresthesias
3. Cardiopulmonary
   1. Bradycardia
   2. Hypoventilation
   3. Pericardial/pleural effusions
4. Dermatologic
   1. Hair loss
   2. Non-pitting edema (periorbital, extremities)
   3. Facial swelling

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. UTZ to look for thyroid nodules

Treatment

1. Depends on etiology
   1. Consider starting levothyroxine daily but doses too high may lead to thyroid storm

Disposition

1. Most hypothyroidism is treated as an outpatient followed in ambulatory clinic
2. Admit and treat severe hypothyroidism or myxedema coma

See Also

• Myxedema Coma
• Thyroid (General)

Source

Tintinalli's