Key Facts

Myxoedema coma is a medical emergency with very high mortality. Early recognition and treatment with IV thyroid hormones and hydrocortisone are essential. It almost always has a precipitant.

Epidemiology

Very rare. More common in elderly women, winter months, long-standing untreated hypothyroidism.

Aetiology

Severe untreated or undertreated hypothyroidism + acute precipitant. Precipitants: infection (UTI, pneumonia — commonest), cold exposure, sedatives/anaesthetics, MI, stroke, trauma, GI haemorrhage, non-adherence to levothyroxine.

Pathophysiology

Severe thyroid hormone deficiency → progressive metabolic decompensation: reduced basal metabolic rate → hypothermia; reduced cardiac output → hypotension; CNS depression → altered consciousness/coma; impaired free water excretion → hyponatraemia; respiratory depression → hypoventilation → CO₂ retention → respiratory failure.

Cardinal Features

• Hypothermia (<35°C, may be <30°C; standard thermometers may not register)
• Altered consciousness: drowsiness → confusion → coma (despite the name, frank coma occurs in minority)
• Bradycardia and hypotension
• Hypoventilation: respiratory failure with CO₂ retention

Other Features

• Non-pitting oedema (face, hands — myxoedema)
• Dry, cool, pale skin
• Hyponatraemia (dilutional — impaired free water excretion)
• Hypoglycaemia
• Pleural/pericardial effusions
• Ileus, constipation, urinary retention

Red Flags

• Hypothermia + altered consciousness in patient with known hypothyroidism or thyroidectomy scar → myxoedema coma
• Respiratory failure → may need mechanical ventilation
• Cardiovascular collapse

Immediate

• TFTs: very high TSH, very low T4 (primary); or low TSH + low T4 (secondary/central)
• U&Es: hyponatraemia (common and significant)
• Blood glucose: hypoglycaemia
• ABG: hypoxia, hypercapnia (CO₂ retention), respiratory acidosis
• Cortisol: assess for coexistent adrenal insufficiency (before steroid administration)
• FBC, CRP, blood cultures: infection screen
• CXR: pleural effusion, pneumonia
• ECG: bradycardia, low voltage, prolonged QT
• Core temperature (low-reading thermometer)

Emergency Treatment (ITU)

1. IV hydrocortisone 100mg STAT (give BEFORE levothyroxine — prevents adrenal crisis); then 50-100mg TDS until adrenal function clarified
2. IV levothyroxine: loading dose 300-500μg IV slowly, then 50-100μg IV daily
3. IV liothyronine (T3): 10-20μg IV then 10μg TDS; consider in severe/refractory cases (more rapid onset than T4)
4. Supportive:
   • Passive rewarming ONLY (warm blankets, warm room); AVOID active rewarming (causes vasodilatation → cardiovascular collapse)
   • IV fluids (cautious — fluid overload risk; correct hyponatraemia with fluid restriction if mild; hypertonic saline if severe/symptomatic)
   • Glucose replacement if hypoglycaemic
   • Mechanical ventilation if respiratory failure
   • Vasopressors if persistent hypotension (noradrenaline)
5. Treat precipitant: antibiotics if infection suspected (even without fever — hypothermia masks pyrexia)

Referral Criteria

• All myxoedema coma: ITU admission
• Endocrinology: urgent consultation

Mortality ~25-60% (higher in elderly, delayed treatment, severe hypothermia, cardiovascular collapse, sepsis). Factors predicting poor outcome: severe hypothermia (<32°C), GCS <8, advanced age, APACHE II score, sepsis. Early recognition and treatment significantly improve survival. Survivors require long-term levothyroxine with adherence support.

Myxoedema Coma — Treatment Priorities

Why Hydrocortisone BEFORE Levothyroxine?

• Thyroid hormone replacement increases cortisol metabolism
• If patient has coexistent adrenal insufficiency (common in polyglandular autoimmune syndrome or central hypothyroidism), giving thyroxine alone may precipitate adrenal crisis
• Always assume adrenal insufficiency until proven otherwise