Endocrine · Topic 7 of 13

Myxedema Coma

Endocrine · thyroid emergency

Myxedema Coma

Severe hypothyroidism with altered mental status and hypothermia. Treat on suspicion: stress-dose hydrocortisone first, then IV levothyroxine.

Key numbers

Give stress-dose hydrocortisone before levothyroxineHC 50–100 mg q6–8h

IV levothyroxine 200–400 mcg loadLT4 200–400 mcg IV

01 · Defined byAltered mental status plus hypothermia

Myxedema coma is decompensated severe hypothyroidism: altered mental status (not always coma) and hypothermia, often with bradycardia, hypoventilation with CO₂ retention, hyponatremia, hypoglycemia and hypotension. Diagnose clinically and treat before labs return.

02 · FirstGive stress-dose hydrocortisone before levothyroxine

Draw a cortisol level, then give IV hydrocortisone 50–100 mg every 6–8 hours before levothyroxine until adrenal insufficiency is excluded: thyroid hormone speeds cortisol clearance and can precipitate adrenal crisis.

03 · GiveIV levothyroxine 200–400 mcg load

Load IV levothyroxine 200–400 mcg (lower end for older or small patients and those with coronary disease or arrhythmia), then 1.6 mcg/kg/day × 0.75 IV daily until oral intake is reliable.

Causes & risk factors

Why it happens

Look for infection and sedating drugsUsually long-standing hypothyroidism tipped over by infection, trauma, cold exposure, stroke or CNS depressants (sedatives, opioids, anesthesia); search for infection and treat it empirically while cultures are pending.

Diagnosis & monitoring

Work-up

High TSH, low free T4 (primary)Primary hypothyroidism shows a high TSH with low free T4; a low or normal TSH with low free T4 points to central (pituitary) disease, where coexisting adrenal insufficiency makes hydrocortisone essential.

Telemetry; free T4 and T3 every 1–2 daysMonitor on telemetry for ischemia and arrhythmia as hormone is replaced; follow mental status, cardiac and pulmonary function, and recheck thyroid hormone levels (free T4, T3) every 1–2 days (ATA).

Do right now

In this order

First moves

Check ABG; ventilate for hypercapnic failure

→

Give stress-dose hydrocortisone before levothyroxineHC 50–100 mg q6–8h

→

IV levothyroxine 200–400 mcg loadLT4 200–400 mcg IV

→

Rewarm passively, not rapidly

Why each step

Check ABG; ventilate for hypercapnic failureHypoventilation from a blunted hypoxic and hypercapnic drive and respiratory muscle myxedema causes CO₂ retention; obtain an ABG and start mechanical ventilation promptly when ventilation is compromised.

Give stress-dose hydrocortisone before levothyroxineDraw a cortisol level, then give IV hydrocortisone 50–100 mg every 6–8 hours before levothyroxine until adrenal insufficiency is excluded: thyroid hormone speeds cortisol clearance and can precipitate adrenal crisis.

IV levothyroxine 200–400 mcg loadLoad IV levothyroxine 200–400 mcg (lower end for older or small patients and those with coronary disease or arrhythmia), then 1.6 mcg/kg/day × 0.75 IV daily until oral intake is reliable.

Rewarm passively, not rapidlyUse passive rewarming with blankets; rapid active rewarming causes vasodilation with hypotension and arrhythmias. Severe hypothermia (24–32 °C) can be missed without a low-reading thermometer.

Management

Orders

Liothyronine IV is an optional add-onIV liothyronine may be added because T4-to-T3 conversion is impaired: 5–20 mcg load, then 2.5–10 mcg every 8 hours (lower in older or cardiac patients); avoid high doses — high T3 is linked to death.

Correct hyponatremia carefully; avoid hypotonic fluidsHyponatremia comes from impaired free-water excretion (excess ADH, low GFR); give fluids cautiously, avoid hypotonic fluids, and correct sodium stepwise — severe hyponatremia (105–120 mEq/L) can itself cause coma.

Support blood pressure and glucoseTreat hypotension with careful volume resuscitation and vasopressors as needed, and check glucose often — hypoglycemia suggests coexisting adrenal or pituitary failure and needs IV dextrose.

Give thyroid hormone IV, not orallyGut edema makes oral absorption unreliable, and the levothyroxine label advises against oral products for myxedema coma; switch to oral when stable (oral dose ≈ IV dose ÷ 0.75).

Dose all drugs cautiouslyDrug metabolism is slowed in severe hypothyroidism, so give sedatives, opioids and other drugs at reduced doses and only when needed.

Myxedema coma or nonthyroidal illness?

Commonly confused

TSH	High
Free T4	Low
Thyroid hormone	IV levothyroxine now

More detail

Reference

Show 4 reference facts

Mortality remains about 25–60% even with prompt treatment; hypotension, respiratory failure, hyponatremia and delayed care predict a poor outcome.

The Popoveniuc score (mental status, thermoregulation, cardiovascular, GI, metabolic findings, precipitant) supports diagnosis: ≥ 60 highly suggestive, < 25 unlikely.

Other clues: nonpitting periorbital and facial edema, macroglossia, hoarse voice, delayed relaxation of deep tendon reflexes, and pericardial or pleural effusions that rarely cause tamponade.

Very high T4 loading doses and advanced age have been associated with higher mortality, supporting the lower end of the loading range in older patients.

Pearl

Steroids before thyroxine: thyroid hormone speeds cortisol clearance and can tip hidden adrenal insufficiency into crisis.

Sources · Merck Manual Professional — Hypothyroidism (Myxedema coma), 2026 · Jonklaas J et al. Guidelines for the Treatment of Hypothyroidism (ATA Task Force on Thyroid Hormone Replacement). Thyroid 2014;24:1670–1751 (recommendations 21a–21d, myxedema coma) · From the Popoveniuc Score to Therapeutic Protocols: A Comprehensive Review of Myxedema Coma. Cureus 2026 · Zhang Y et al. Myxedema coma: challenges and future directions, a systematic survey and review. Thyroid Res 2025 · Synthroid (levothyroxine sodium) prescribing information — DailyMed (§5.3 myxedema coma, §5.4 adrenal crisis) · Merck Manual Professional — Euthyroid Sick Syndrome, Jan 2026 · Starter sheet built from the verified AGACNP fact map (facts reviewed 2026-10-15).