Hypothyroidism

Background

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

Etiology

  • Primary
    • 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
    • Idiopathic
  • Secondary
    • 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
    • Weight 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

Differential Diagnosis

  • Addison's disease
  • Chronic fatigue syndrome
  • Constipation
  • Depression
  • Sick Euthyroidism
  • Hypopituitarism
  • Hypothermia
  • Iodine Deficiency

Evaluation

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
  • ECG - bradycardia, low voltage
  • VBG - hypercapnia from hypoventilation, possibly compensated if chronic

Categorization

Type Cause TSH FT4
Primary Failure of thyroid Elevated Low
Secondary Failure of pituitary Low Low
Tertiary Failure of hypothalamus

Management

Disposition

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

See Also

References