Hypothyroidism

Background

  • 3-10x more common in females
  • Peak incidence age >60
  • Emergent manifestation of severe hypothyroid = myxedema coma

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)

Spectrum of Thyroid Disease

Clinical Features

  • Constitutional
  • Neuropsychiatric
  • Cardiopulmonary
    • Bradycardia
    • Hypoventilation
    • Pericardial/pleural effusions
  • Dermatologic
    • Hair loss
    • Non-pitting edema (periorbital, extremities)
    • Facial swelling

Differential Diagnosis

Symptomatic bradycardia

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
PrimaryFailure of thyroidElevatedLow
SecondaryFailure of pituitaryLowLow
TertiaryFailure of hypothalamus

Management

Disposition

  • Most hypothyroidism is treated as an outpatient
  • Admit and treat severe hypothyroidism or myxedema coma

See Also

References

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