Myxedema Coma

Myxedema coma is life-threatening decompensated hypothyroidism. Despite its name, the person may be confused, obtunded, or delirious rather than comatose. The defining problem is failure of the body’s metabolic drive: cellular oxygen use falls, heat production drops, respiratory effort weakens, cardiac output declines, and multiple organs slow down together. Hypothermia is not merely a sign of exposure. Low thyroid hormone reduces thermogenesis, so the patient cannot generate enough heat to maintain temperature. Hypoventilation follows from reduced central respiratory drive and weak respiratory muscles, allowing carbon dioxide to accumulate. Bradycardia and reduced myocardial contractility lower cardiac output, while impaired renal water clearance contributes to dilutional hyponatremia. The result can resemble a patient whose systems are gradually powering down: colder, slower, sleepier, and less able to compensate for infection, sedatives, hypoglycemia, or fluid shifts. A minor stressor can push a person with longstanding untreated or undertreated hypothyroidism into crisis.