Myxedema coma

Background

1. Hypothyroidism + mental status changes/coma + hypothermia + precipitating stressor
   1. 80% mortality
2. Occurs in 0.1% of patients with hypothyroidism

Precipitants

1. Infection
   1. Bradycardia and hypothermia may mask usual signs of fever
2. Cold exposure
3. Trauma
4. MI
5. CHF
6. CVA
7. GI bleed
8. Metabolic conditions (hypoxia, hypercapnia, hyponatremia, hypoglycemia)
9. Burns
10. Meds: B-blockers, sedatives, narcotics, phenothiazine, amiodarone
11. Medication non-compliance (thyroid meds)

Diagnosis

1. Hypothermia
   1. So common in myxedema that a normal temperature should suggest an underlying infection
   2. Absence of shivering distinguishes from accidental hypothermia
2. Cardio
   1. Bradycardia
   2. Hypotension
3. Pulm
   1. Hypoventilation -> respiratory collapse
      1. CO2 narcosis
   2. Pleural effusions
   3. Upper airway obstruction from glottic edema, vocal cord edema, and macroglossia
4. Neuro
   1. AMS/coma

Work-Up

1. Chemistry
2. CBC
3. TSH, FT4, FT3
4. Cultures
5. LFT
6. Cortisol level
7. VBG
8. CXR
9. EKG

DDx

1. Sepsis
2. Depression
3. Adrenal crisis
4. CHF
5. Hypoglycemia
6. CVA
7. Hypothermia
8. Drug overdose
9. Meningitis

Treatment

1. Supportive care
   1. Respiratory distress
      1. Mechanical ventilation if needed
   2. Hypoglycemia
      1. IV dextrose
   3. Hyponatremia
      1. Water restriction
   4. Hypotension
      1. Vasopressors (ineffective w/o thyroid hormone replacement)
      2. Hydrocortisone 100mg q8hr IV (adrenal insufficiency may also be present)
         1. Give first dose before starting thyroid replacement therapy
   5. Hypothermia
      1. Treat w/ passive rewarming (active rewarming may cause hypotension)
2. Thyroid replacement therapy
   1. Optimal regimen is controversial
   2. Can give T3 or T4 or both
   3. T4
      1. Advantages
         1. Smooth, slow steady onset of action
         2. May be safer in pts with CAD
      2. Disadvantages
         1. Requires extrathyroidal conversion of T4 -> T3 to work (may be reduced in myxedema)
      3. Dose: Start 4mcg/kg IV followed by 100mcg IV in 24hr
   4. T3
      1. Advantages
         1. Does not require extrathyroidal action to work
         2. Rapid onset of action
      2. Disadvantages
         1. Rapid onset of action (may not be desirable in pts w/ CAD)
      3. Dose: 20mcg IV followed by 10mcg q8hr until pt is conscious
         1. Start with 10mcg if elderly or has CAD
3. Treaty precipitating factors

Disposition

1. Admit to ICU
2. Endocrine consult

See Also

• Hypothyroidism
• Thyroid (General)

Source

Tintinalli's