⚠️ Myxedema Coma: The Hypothyroid Crisis You Can’t Miss on the USMLE
Myxedema coma is a rare but fatal complication of long-standing or untreated hypothyroidism. It’s classically tested on Step 1 and Step 2 due to its dramatic presentation, classic triggers, and urgent management.
USMLE Buzzwords: Hypothermia + altered mental status + bradycardia in an elderly woman with history of hypothyroidism.
🧬 Pathophysiology
Severe thyroid hormone deficiency leads to slowed metabolism, affecting all organ systems
↓ cardiac output, ↓ respiration, ↓ CNS activity
Precipitating factors (infection, cold exposure, drugs) overwhelm already impaired systems
⚠️ Common Triggers
| Category | Examples |
|---|---|
| Infections | Pneumonia, sepsis, UTI |
| Cold exposure | Winter months, elderly neglect |
| Drugs | Sedatives, narcotics, lithium, amiodarone |
| Trauma/surgery | Post-op state |
| Noncompliance | Stopped levothyroxine |
🧪 Clinical Features
| System | Finding |
|---|---|
| CNS | Lethargy, coma, confusion |
| Cardiovascular | Bradycardia, hypotension |
| Respiratory | Hypoventilation, CO₂ retention |
| Thermoregulation | Hypothermia (often < 35°C) |
| Skin | Dry, cold, puffy face |
| GI/renal | Hypoglycemia, hyponatremia, ↓ GFR |
🧫 Lab Findings
| Test | Expected Result |
|---|---|
| TSH | ↑ (if primary hypothyroidism) |
| Free T3, T4 | ↓↓↓ |
| Sodium | ↓ |
| Glucose | ↓ |
| ABG | CO₂ retention ± metabolic acidosis |
USMLE Tip: Check TSH + T4 even in altered mental status if hypothyroidism is on the differential.
💊 Emergency Management
| Step | Treatment |
|---|---|
| 1 | IV levothyroxine ± liothyronine |
| 2 | IV hydrocortisone (prevent adrenal crisis) |
| 3 | Passive rewarming (blankets only) |
| 4 | Treat underlying cause (infection, drugs) |
| 5 | Supportive care: airway, glucose, fluids, electrolytes |
⚠️ Always give steroids before or with thyroid hormone to avoid precipitating adrenal crisis.
📚 Sample USMLE Vignette
A 70-year-old woman presents in January with confusion and hypothermia. HR is 48, BP is 90/60, T is 34.5°C. She has a history of hypothyroidism but stopped medications 2 months ago. Labs show ↑ TSH, ↓ T3/T4, and low sodium.
✅ Answer: Myxedema coma — initiate IV levothyroxine and hydrocortisone immediately.
📲 Call to Action
❄️ Cold, slow, and deadly — don’t miss this USMLE emergency.
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