Hypothyroidism

Basics

Description

  • Decreased level of thyroid hormone leads to a variety of clinical manifestations
  • More common in women, the elderly, and those with autoimmune diseases
  • Myxedema coma is a rare, extreme form of hypothyroidism characterized by altered mental status and defective thermoregulation triggered by a precipitating event in a patient with hypothyroidism

Etiology

  • Primary:
    • Idiopathic
    • Congenital
  • Autoimmune:
    • Thyroiditis
    • Hashimoto disease (most common cause in iodide sufficient countries)
  • Iatrogenic:
    • Postsurgical
    • External radiation
    • Radioiodine therapy (Wolff–Chaikoff effect)
  • Drugs:
    • Iodides, lithium, amiodarone, sunitinib, bexarotene, interferons, narcotics, sedatives, rifampin
    • Phenytoin and carbamazepine increase clearance of T4 in patients with hypothyroidism taking T4
  • Neoplasm:
    • Primary (carcinoma) or secondary (infiltration)
  • Infection:
    • Viral (rarely aerobic or anaerobic bacteria)
  • Iodine deficiency (most common cause worldwide)
  • Central (very rare):
    • Pituitary or hypothalamic disorder induced by drugs or severe illness
    • May have other associated hormone deficiencies
  • Myxedema coma:
    • Life-threatening decompensation of a patient with hypothyroidism due to a stress, often during winter months
    • Stressors include:
      • Infection
      • Hypothermia
      • Intoxication
      • Drugs (eg, opioids)
      • Cerebrovascular accident
      • Heart failure
      • Trauma

Pregnancy Considerations

  • Hypothyroidism has been associated with preterm delivery, placental abruption, preeclampsia, low birth weight, and increased rate of Caesarean section
  • Hypothyroid women require increased exogenous thyroid hormone replacement during pregnancy above baseline
  • Postpartum thyroiditis occurs in up to 10% of women:
    • Usually 3–6 mo postpartum
    • Typically resolves without treatment

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