Hypothyroidism

Background

• 3-10x more common in females
• Peak incidence age >60

Types

• Primary: failure of thyroid
  • elevated TSH, low FT4
• Secondary: failure of pituitary
  • low TSH, low FT4
• Tertiary: failure of hypothalamus

Etiology

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

Clinical Features

• Constitutional
  • Cold intolerance
  • Wt gain
  • Weakness
  • Lethargy
  • Hypothermia
  • Hoarse voice
  • Hair loss
  • Constipation
  • Dysfunctional uterine bleeding
• Neuropsychiatric
  • Delayed relaxation of DTRs
  • Paresthesias
• Cardiopulmonary
  • Bradycardia
  • Hypoventilation
  • Pericardial/pleural effusions
• Dermatologic
  • Hair loss
  • Non-pitting edema (periorbital, extremities)
  • Facial swelling

Diagnosis

Work-up

• TSH
• Total and Free T4
• Total and Free T3
• Thyroid Binding Globulin (TBG)
• Auto-antibodies (anti-TPO, anti-microsomal, anti-Tg)
• Thyroid ultrasound
• EKG - bradycardia, low voltage

Management

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

Disposition

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

See Also

• Myxedema coma
• Thyroid (Main)