Updated July 2026 · 8 min read
Part of the ICU Emergencies Hub — browse every related guide in one place.
If thyroid storm is the body running too hot, myxedema coma is the body winding down to a stop. It is the extreme, decompensated end of hypothyroidism: metabolism, temperature, breathing, heart rate, and consciousness all slow together. The name is misleading — most patients are not truly comatose and rarely have the classic skin swelling — but the mortality is genuinely high, and it hits older patients in winter, often triggered by infection, cold exposure, sedatives, or a missed levothyroxine dose. Because everything is slow, it is easy to under-read; the nurse who connects hypothermia to hyponatremia to altered mentation is the one who names it.
The findings all flow from a metabolism turned down to idle. The patient is cold because heat production has collapsed, and this hypothermia can be profound and is often the tip-off. Breathing is shallow and slow, so carbon dioxide climbs and the patient becomes obtunded partly from CO2 narcosis. The heart is slow, the blood pressure low, and the sodium is low because free water cannot be cleared. Reflexes show the classic delayed relaxation phase. Mental status ranges from lethargy and confusion to true coma or seizures.
| System | Finding in myxedema coma |
|---|---|
| Temperature | Hypothermia, sometimes below 32°C; may mask an infection's usual fever |
| Respiratory | Hypoventilation, hypercapnia, hypoxia — a major driver of the depressed sensorium |
| Cardiovascular | Bradycardia, hypotension, low voltage on ECG, pericardial effusion |
| Metabolic / neuro | Hyponatremia, hypoglycemia, obtundation, delayed reflexes, seizures |
The thyroid replacement itself is given intravenously because gut absorption is unreliable in a shut-down patient. Levothyroxine (T4) is the mainstay, sometimes combined with a small amount of liothyronine (T3) since peripheral conversion is impaired — but T3 is used cautiously in the elderly and those with cardiac disease because it is more likely to provoke arrhythmia and ischemia.
Rewarm this patient passively with blankets and a warm environment. Aggressive active external rewarming causes peripheral vasodilation that can drop an already low blood pressure into circulatory collapse — the correct heat comes from restoring the metabolism, not from a warming device fighting the physiology. The hyponatremia is usually a free-water problem, so fluids are given thoughtfully with attention to sodium; over-rapid sodium correction risks its own neurologic injury, and free-water restriction is often part of the plan. Because these patients are exquisitely sensitive to sedatives and opioids, hold or minimize anything that further depresses respiration and mentation.
Myxedema coma is the quiet emergency — cold, slow, and easy to under-triage — but it kills when it is missed. Recognize the pattern of hypothermia, hypoventilation, hyponatremia, and a dulled sensorium in a hypothyroid or elderly patient; give steroids before or with the thyroid hormone; rewarm passively; support ventilation and sodium carefully; and go looking for the hidden infection. The nurse who trusts the pattern over the unremarkable-looking vitals is the one who gets treatment started in time.
Related: Thyroid storm · Adrenal crisis · Hyponatremia: CSW vs SIADH · Hydrocortisone
Educational content for licensed clinicians. Always follow your facility's protocol and provider orders. Not medical advice.
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