Myxedema coma
Background
- Extreme, decompensated hypothyroidism with end-organ dysfunction
- True endocrine emergency with mortality 30-60% even with treatment[1]
- Misnomer: patients are not always comatose and myxedema is not always present
- Most common in elderly women with undiagnosed or undertreated hypothyroidism
- Precipitants:
- Infection/sepsis (most common trigger)
- Cold exposure, hypothermia
- Medication non-compliance with levothyroxine
- Surgery, trauma, MI, stroke
- Medications: amiodarone, lithium, sedatives, opioids, anesthetics
- Adrenal crisis (concurrent adrenal insufficiency)
Clinical Features
- Classic triad: altered mental status + hypothermia + precipitating event
- Altered mental status: confusion, lethargy, obtundation → coma
- Hypothermia (may be severe, <32C; absence of fever despite infection is classic)
- Bradycardia and hypotension (refractory to vasopressors until thyroid hormone replaced)
- Hypoventilation with hypercapnia and hypoxia (respiratory failure)
- Hyponatremia (due to decreased free water excretion — SIADH-like)
- Hypoglycemia (concurrent adrenal insufficiency or hepatic dysfunction)
- Non-pitting edema (myxedema), periorbital swelling
- Delayed deep tendon reflexes (hung-up reflexes)
- Ileus, urinary retention, hypothermia
- Pericardial effusion (may rarely cause tamponade)
Differential Diagnosis
- Sepsis (most common precipitant AND mimic)
- Hypothermia (primary environmental)
- Adrenal crisis
- Stroke / intracranial pathology
- Drug overdose (opioids, sedatives)
- Hypoglycemia
- Heart failure
Evaluation
- TSH: markedly elevated in primary hypothyroidism (most common)
- May be low/normal in central (pituitary/hypothalamic) hypothyroidism
- Free T4: very low or undetectable
- Free T3: low (but less reliable)
- BMP: hyponatremia (present in ~50%), hypoglycemia
- CBC: may show anemia, leukopenia
- ABG/VBG: respiratory acidosis, hypercapnia, hypoxemia
- Cortisol level (before starting steroids) — rule out concurrent adrenal insufficiency
- Lactate: if concern for sepsis
- ECG: bradycardia, low voltage, prolonged QT, possible J (Osborn) waves
- CXR: cardiomegaly (pericardial effusion), pleural effusion
- Infectious workup: blood/urine cultures, CXR (infection is most common precipitant)
Management
Immediate
- Airway management: intubation for respiratory failure or severe AMS
- Passive rewarming (avoid active external rewarming which can cause vasodilation and cardiovascular collapse)
- IV access, cardiac monitoring
- Treat precipitant (antibiotics for suspected infection, dextrose for hypoglycemia)
Thyroid Hormone Replacement
- IV levothyroxine (T4) is the mainstay:
- Loading dose: 200-400 mcg IV (or 4 mcg/kg lean body weight)
- Then 50-100 mcg IV daily
- IV liothyronine (T3) may be added for severe cases:
- 5-20 mcg IV loading dose, then 2.5-10 mcg IV q8h
- T3 has faster onset of action (~4 hours vs 24 hours for T4)
- Use with caution in elderly / cardiac patients (arrhythmia risk)
- Route must be IV — GI absorption unreliable due to ileus and mucosal edema
Stress-Dose Steroids
- Hydrocortisone 100 mg IV q8h — give BEFORE or concurrent with thyroid hormone[2]
- Rationale: thyroid hormone replacement increases cortisol metabolism; if concurrent adrenal insufficiency exists, this can precipitate adrenal crisis
- Discontinue steroids once adrenal insufficiency ruled out
Supportive Care
- Fluid restriction if severe hyponatremia (dilutional)
- Avoid hypotonic fluids (worsens hyponatremia)
- Cautious IV NS for hypotension
- Vasopressors may be needed but often refractory until thyroid hormone takes effect
- Avoid sedatives and opioids (impair respiratory drive)
- Electrolyte correction (hyponatremia, hypoglycemia)
Disposition
- ICU admission for all patients
- Serial monitoring: TSH, free T4, electrolytes, glucose, cortisol
- Improvement in vital signs expected within 24-48 hours
- Mental status may take days to weeks to normalize
- Long-term oral levothyroxine replacement once stabilized
See Also
References
- Mathew V, et al. Myxedema coma: a new look into an old crisis. J Thyroid Res. 2011;2011:493462. PMID 22028977
- Klubo-Gwiezdzinska J, Wartofsky L. Thyroid emergencies. Med Clin North Am. 2012;96(2):385-403. PMID 22443982
- Wall CR. Myxedema coma: diagnosis and treatment. Am Fam Physician. 2000;62(11):2485-2490. PMID 11130234