Myxedema Coma

Myxedema coma is life-threatening decompensated hypothyroidism. The name is misleading: many patients are profoundly lethargic, confused, or obtunded rather than truly comatose. Thyroid hormone normally sustains basal metabolism, heat production, cardiac chronotropy, and ventilatory drive. When hormone levels become critically low, the body slows across several systems at once. Heat generation falls, producing hypothermia. Cardiac rate and contractility fall, reducing cardiac output and tissue perfusion. Ventilation becomes shallow, so carbon dioxide accumulates and worsens somnolence. Reduced renal free-water clearance contributes to dilutional hyponatremia. This is not simply “very low thyroid hormone.” It is a failure of the body’s ability to maintain temperature, oxygenation, circulation, and consciousness. Infection, cold exposure, surgery, trauma, myocardial infarction, stroke, gastrointestinal hemorrhage, sedatives, opioids, anesthetics, and stopping thyroid replacement can push a person with longstanding hypothyroidism into this state.