Myxedema coma is a rare life-threatening complication of hypothyroidism characterized by profound lethargy or coma and usually accompanied by hypothermia.

• Mental obtundation, profound lethargy or coma
• Hypothermia (rectal temperature <35° C [95° F]); often missed by using ordinary thermometers graduated only to 34.5° C (94.1° F) or because the mercury is not shaken below 36° C (96.8° F)
• Bradycardia, hypotension (attributable to circulatory collapse)
• Delayed relaxation phase of deep tendon reflexes, areflexia
• Myxedema facies (Fig. E1)
• Alopecia, macroglossia, ptosis, periorbital edema, nonpitting edema, doughy skin
• Bladder dystonia and distention
• Pleural, pericardial, and peritoneal effusions

Decompensation of hypothyroidism from:

• Sepsis
• Exposure to cold weather
• Central nervous system depressants (sedatives, narcotics, antidepressants)
• Trauma, surgery
• Stroke, congestive heart failure, burns
• Intravascular volume contraction (GI blood loss, diuretic use)
• Myocardial infarction
• Metabolic derangements

• Severe depression, primary psychosis
• Drug overdose
• Cerebrovascular accident, liver failure, renal failure
• Hypoglycemia, CO₂ narcosis, encephalitis

Diagnosis of hypothyroidism and exclusion of contributing factors (e.g., sepsis, cerebrovascular accident) with laboratory and radiographic studies

• Serum thyroid stimulating hormone and T₄ levels should be tested immediately. Results reveal markedly increased thyroid-stimulating hormone (if primary hypothyroidism), decreased serum free T₄.
• Complete blood count with differential, urine and blood cultures to rule out infectious process
• Electrolytes, blood urea nitrogen, creatinine, liver function tests, calcium, glucose
• Arterial blood gases to rule out hypoxemia and carbon dioxide retention
• Stat cortisol level to rule out concomitant adrenal insufficiency prior to initiation of thyroid hormone replacement
• Elevated creatine phosphokinase may be present
• Hyperlipidemia is common

• CT scan of head in suspected cerebrovascular accident
• Chest x-ray to rule out infectious process

• Prevent further heat loss; cover the patient but avoid external rewarming because it may produce vascular collapse. Consider warmed IV fluids.
• Support respiratory function; intubation and mechanical ventilation may be required.
• Monitor patient in the intensive care unit.

• Give levothyroxine 5 to 8 mcg/kg (200 to 500 mcg) IV infused over 15 min, then 50 to 100 mcg IV q24h until transition to an oral formulation is possible. Oral daily dose following IV administration is 1.6 mcg/kg. Lower doses may be indicated in patients with cardiac disease or advanced age.
• Glucocorticoids should also be empirically administered until coexistent adrenal insufficiency can be ruled out. Hydrocortisone hemisuccinate 100 mg IV bolus is initially given, followed by 100 mg IV q8h until initial plasma cortisol level is confirmed normal.
• IV hydration with D₅NS is used to correct hypotension and hypoglycemia (if present); avoid overhydration and possible water intoxication because clearance of free water is impaired in these patients.
• Rule out and treat precipitating factors (e.g., antibiotics in suspected sepsis).

Mortality rate in myxedema coma is high, up to 40% despite aggressive therapy.

If the diagnosis is suspected, initiate treatment immediately without waiting for confirming laboratory results.