Myxedema Coma: Definition and Clinical Features
Myxedema coma is a life-threatening endocrine emergency representing the extreme manifestation of severe hypothyroidism, characterized by altered mental status, hypothermia, bradycardia, hypotension, hypoventilation, and potential multisystem organ failure. 1, 2, 3
Core Clinical Presentation
The hallmark features that define myxedema coma include:
- Altered mental status or coma - ranging from confusion and lethargy to complete unresponsiveness, which gives the condition its name 2, 3, 4
- Hypothermia - body temperature often below 35°C (95°F), which may be profound and slow to respond to warming measures 3, 4
- Cardiovascular collapse - including bradycardia, hypotension, and reduced cardiac output from impaired myocardial contractility 2, 4
- Respiratory failure - hypoventilation with hypercarbia and hypoxia, often requiring mechanical ventilation 2, 5
- Hyponatremia - due to impaired free water clearance 2, 3
Precipitating Factors
Myxedema coma typically occurs in patients with longstanding, untreated or undertreated hypothyroidism when triggered by a physiologic stressor:
- Infection or sepsis is a common precipitant that can unmask severe hypothyroidism 6, 3
- Surgery or trauma represents major physiologic stress that can trigger decompensation 6
- Medications including sedatives and anesthetics can precipitate myxedema coma 1
- Hypoglycemia must be identified and corrected immediately as it can both precipitate and complicate myxedema coma 6
Biochemical Profile
The typical laboratory findings include:
- Severely elevated TSH (often >100 mIU/L) with very low or undetectable free T4 in primary hypothyroidism 3, 4
- Acute kidney injury with elevated creatinine 2, 3
- Elevated creatine phosphokinase reflecting muscle breakdown 7
- Metabolic acidosis from impaired cellular metabolism 7
- Hypoglycemia which requires immediate correction 6, 4
Critical Diagnostic Considerations
Myxedema coma can rarely occur even with subclinical hypothyroidism (elevated TSH with normal free T4), though this is extremely unusual and may reflect deviation from a higher pre-morbid set-point. 7
Central hypothyroidism (low or inappropriately normal TSH with low free T4) can also present as myxedema coma, particularly at initial diagnosis, and carries the same high mortality risk. 5
Cardiovascular Complications
- Cardiogenic shock from severely reduced left ventricular ejection fraction and impaired contractility represents a particularly severe complication with increased mortality 2
- Pericardial effusion may be present on echocardiography 4, 7
- Cardiac arrest with pulseless electrical activity can occur, requiring cardiopulmonary resuscitation 2
- Heart block may develop as part of the cardiovascular manifestations 5
Immediate Management Priorities
The treatment of myxedema coma requires urgent, aggressive intervention:
- Intravenous thyroid hormone replacement must be initiated immediately, with IV liothyronine (T3) preferred for rapid onset of action 1, 3
- Glucocorticoid administration is mandatory and should be given simultaneously, as hypothyroidism decreases cortisol clearance and adrenal insufficiency may coexist 1, 2
- Correction of hypoglycemia must occur immediately upon identification 6
- Vasopressor support for hypotension and circulatory collapse 2
- Mechanical ventilation for respiratory failure with hypoventilation 2, 5
- Aggressive rewarming for hypothermia, though response may be slow initially 3
- Treatment of precipitating factors such as infection with appropriate antibiotics 3
Prognosis and Long-Term Considerations
Myxedema coma carries a high mortality rate even with appropriate treatment, making rapid diagnosis and individualized aggressive management critical for survival. 2, 4
Following recovery, long-term management focuses on: