Hypothyroidism may be caused by multiple factors. Myxedema coma is a rare, life-threatening expression of hypothyroidism. It may be precipitated by infection, cold exposure, trauma, medications, or myocardial infarction. It classically occurs during the winter months in elderly women with undiagnosed or undertreated hypothyroidism.
The presentation of hypothyroidism is summarized in Figure 131-1. Patients with myxedema coma have hypothyroidism and present with hypothermia, bradycardia, hypotension, and altered mental status. Respiratory failure is common and a difficult airway may be encountered due to macroglossia and oropharyngeal edema. Laboratory abnormalities include hypoglycemia and hyponatremia.
Symptoms and signs of hypothyrodism.
Diagnosis and Differential
Myxedema coma is a clinical diagnosis. Send confirmatory thyroid studies, but do not delay treatment for test results. Low free thyroxine (FT4) and triiodothyronine (FT3), and elevated thyroid stimulating hormone (TSH) are diagnostic. The differential diagnosis for myxedema coma includes sepsis, adrenal crisis, congestive heart failure, hypoglycemia, stroke, hypothermia, and drug overdose.
Emergency Department Care and Disposition
Provide supportive care with airway stabilization, mechanical ventilation, and cardiac monitoring (Table 131-1). Treat hypotension with fluid resuscitation. Vasopressors may be ineffective until thyroid hormone replacement is initiated. Passively rewarm hypothermic patients.
Seek out and treat precipitating causes. Administer hydrocortisone 100 milligrams IV for suspected adrenal insufficiency. Correct hypoglycemia.
Administer levothyroxine (T4) 4 micrograms/kilogram IV by slow infusion. Add liothyronine (T3) 20 micrograms IV for severe myxedema coma. Use liothyronine with caution in the elderly and patients with cardiovascular disease.
Patients should be admitted to a monitored or ICU setting.
Table 131-1 Treatment for Myxedema Coma Supportive Care ||Download (.pdf)
Table 131-1 Treatment for Myxedema Coma Supportive Care
- Airway, breathing, and circulation support: ensure airway control, oxygen, IV access, and cardiac monitor
- IV therapy: dextrose for hypoglycemia; water restriction for hyponatremia
- Vasopressors: if indicated (ineffective without thyroid hormone replacement)
- Hypothermia: treated with passive rewarming using blanket
- Steroids: hydrocortisone (because of increased metabolic stress; 100 to 200 milligrams IV)
Thyroid replacement therapy (see discussion Thyroid Replacement in text)
- IV T4 (levothyroxine) at 4 micrograms/kilogram, followed in 24 h by 100 micrograms IV, then 50 micrograms IV until oral medication is tolerated. (Switch to 50 to 200 micrograms/d PO when patient is ambulatory.)
- IV T3 (liothyronine or triiodothyronine) for myxedema coma at 20 micrograms followed by 10 micrograms IV every 8 h until the patient is conscious (given because of the risk of decreased T3 generation from T4 in severely hypothyroid patients). Start with no more than 10 micrograms IV for the elderly or those with coronary artery disease.
- Either T4 or T3 can be used, but ...