Myxedema coma

Definition

Myxedema coma is the life-threatening decompensation of severe, usually long-standing hypothyroidism. It is characterized by impaired consciousness up to coma, marked hypothermia and respiratory depression.

Aetiopathogenesis

Those affected usually have long-standing, often unrecognized or inadequately replaced hypothyroidism. Typical precipitating factors are:

• acute illness, particularly infection
• trauma
• drugs or substances that depress the central nervous system
• exposure to cold

Pathophysiology: hormone deficiency lowers the basal metabolic rate and heat production. Respiratory drive and respiratory muscles are weakened, leading to carbon dioxide retention and hypoxemia. Free water excretion is reduced, which favors hyponatremia. Drugs are metabolized more slowly. In central hypothyroidism, adrenal insufficiency may also be present.

Clinical features

• Consciousness: somnolence up to coma, seizures
• Hypothermia: body temperature of 24 to 32.2 °C; it is easily missed unless a low-reading thermometer is used
• Breathing: respiratory depression with carbon dioxide retention
• Neurology: areflexia
• Cardiovascular: bradycardia, pericardial effusion; pleural effusions
• Signs of hypothyroidism: puffy face with periorbital swelling, doughy, dry skin, macroglossia, coarse hair
• With a central cause: hypoglycemia and hypotension due to accompanying adrenal or growth hormone insufficiency

Diagnosis

The diagnosis is made rapidly on the basis of history and clinical findings; laboratory tests confirm it.

• Thyroid function: low fT4; TSH markedly raised in primary hypothyroidism, low or normal with a central cause
• Blood gas analysis: hypercapnia and hypoxemia
• Laboratory tests: sodium (hyponatremia), glucose (hypoglycemia), CK, cholesterol, blood count; cortisol to detect accompanying adrenal insufficiency
• Core body temperature with a suitable thermometer
• ECG and echocardiography: bradycardia, pericardial effusion
• Search for the trigger: e.g. infection work-up, drug history

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Further reading (open access)

1. MSD Manual Professional: Hypothyroidism (Myxedema coma)
2. Mathew et al.: Myxedema Coma – A New Look into an Old Crisis (J Thyroid Res 2011)

Cross-references