Myxoedema Coma

OVERVIEW

• extreme form of hypothyroidism
• high mortality

CLINICAL FEATURES

• stupor
• hypothermia
• respiratory failure
• confusion
• coma

• dry skin
• sparse hair
• hoarse voice
• periorbital oedema

• CVS: non-pitting oedema of hands and feet, bradycardia, hypotension refractory to vasopressors, reduced contractility, pericardial effusion
• RESP: respiratory depression, impaired respiratory muscle function, hypoxia and hypercapnia
• RENAL: bladder atony, urinary retention, urinary Na+ normal or high
• ELECTROLYTES: hyponatraemia from increased H2O reabsorption from high levels of ADH
• GI: macroglossia, anorexia, abdominal pain, constipation, ileus
• CNS: delayed tendon reflexes, slow mentation, depression -> psychosis, seizures

Risk or Precipitating Factors

• hypothermia
• CVA
• CHF
• infections
• drugs: anaesthetics, sedatives, narcotics, amiodarone, lithium
• GIH
• trauma
• electrolytes: hypoglycaemia, hyponatraemia
• acidosis
• hypoxaemia
• hypercapnia

INVESTIGATIONS

• TSH: markedly elevated in 95% of cases, 5% are caused by central TSH failure
• low free T4
• low T3

• hyponatraemia
• hypoglycaemia
• anaemia
• hypercholesterolaemia
• high LDH
• high CK

MANAGEMENT

Resuscitate

• admit to ICU because if high mortality and multi-faceted therapy
• may require intubation for various reasons (respiratory failure, airway obstruction from macroglossia, coma)
• ventilation may be required for several days -> weeks
• IV fluid resuscitation and vasoactive agents until thyroid hormone action begins
• warm patient and pre-empt vasodilation and hypotension

Acid-base and Electrolytes

• supportive care
• glucose
• hyponatraemia: cautious correction over time (<10mmol/L day)

Specific Therapy

• hydrocortisone 100mg Q 6hourly if adrenal or pituitary insufficiency suspected
• replacement of thyroid hormones (T4 or T3 is controversial):
  (1) T4 – loading dose = 500mcg IV -> 50-100mcg OD IV or orally
  (2) T3 – loading dose = 10mcg IV -> 10mcg Q4 hrly for 24 hours then every 6 hours

Underlying Cause

• treat precipitant (withdraw drugs, treat infection…)