What are the diagnostic criteria for myxedema crisis?

Diagnostic Criteria for Myxedema Crisis

Myxedema crisis is a clinical diagnosis based on severe decompensated hypothyroidism with altered mental status, hypothermia, and multiple organ dysfunction, requiring a high index of suspicion for prompt diagnosis and treatment.

Core Diagnostic Features

• Altered mental status - ranging from confusion and lethargy to coma (Glasgow Coma Score ≤8 may require intubation) 1
• Hypothermia - often profound and resistant to rewarming efforts 1
• History of hypothyroidism or risk factors (especially discontinuation of thyroid supplements) 1
• Precipitating event - such as infection, trauma, burns, medication discontinuation, or exposure to cold 2, 1

Laboratory Findings

• Thyroid function tests:
  • Low free T4 with inappropriately normal or low TSH 1
  • Low T3 levels 1
• Supportive laboratory findings:
  • Hyponatremia 1, 3
  • Hypoglycemia (requires immediate correction) 4
  • Hypercapnia (respiratory depression) 1, 3
  • Anemia 1
  • Elevated creatine kinase 1
  • Elevated liver enzymes 1

Clinical Manifestations

• Cardiovascular:

  • Bradycardia 1
  • Hypotension 1, 3
  • Cardiogenic shock 1
  • Pericardial/pleural effusions 1
  • Increased risk of arrhythmias 1

• Respiratory:

  • Hypoventilation 1, 3
  • Respiratory failure requiring mechanical ventilation 1
  • CO2 retention 1

• Neurological:

  • Decreased reflexes 1
  • Seizures (less common) 1
  • Delayed relaxation phase of deep tendon reflexes 1

• Gastrointestinal:

  • Ileus 1
  • Megacolon 1

• Dermatological:

  • Non-pitting edema 1
  • Dry, coarse skin 1

Risk Factors for Poor Prognosis

• Hypotension at presentation 1
• Bradycardia at presentation 1
• Need for mechanical ventilation 1
• Hypothermia unresponsive to treatment 1
• Sepsis 1
• Intake of sedative drugs 1
• Lower Glasgow Coma Scale 1
• High APACHE II scores 1
• SOFA scores >6 1

Diagnostic Approach

1. Clinical suspicion based on altered mental status and hypothermia in a patient with known or suspected hypothyroidism 1, 5
2. Immediate thyroid function testing (TSH, free T4, T3) 1
3. Rule out concurrent adrenal insufficiency before initiating thyroid hormone replacement 4
4. Identify precipitating factors through:
   • Complete blood count 1
   • Blood cultures if infection suspected 1
   • Chest X-ray 1
   • Urinalysis 1
   • Medication review (especially for recent discontinuation of thyroid supplements) 1, 5

Differential Diagnosis

• Sepsis 1
• Stroke 1
• Drug overdose 1
• Metabolic encephalopathy 1
• Hypothermia from other causes 1

Important Pitfalls to Avoid

• Delayed diagnosis - maintain high index of suspicion in patients with altered mental status and hypothermia 2, 5
• Failure to identify precipitating factors - especially infections which require concurrent treatment 1
• Overlooking adrenal insufficiency - can be precipitated by thyroid hormone replacement 4
• Inadequate supportive care - requires ICU management 4
• Inappropriate thyroid hormone replacement - dosing should consider age and cardiovascular risk factors 4

Remember that myxedema crisis carries a high mortality rate even with appropriate treatment, making early recognition and aggressive management essential 1, 5.