In a patient presenting to the emergency department with myxedema coma, altered mental status, and hypothermia, which thyroid hormone replacement regimen may be started in the ED and continued in the ICU?

Myxedema Coma: Thyroid Hormone Replacement Strategy

For myxedema coma presenting with altered mental status and hypothermia, initiate intravenous levothyroxine with or without intravenous liothyronine in the emergency department and continue in the ICU. 1, 2, 3

Critical Pre-Treatment Requirement

• Before administering any thyroid hormone, give hydrocortisone 100 mg IV every 8 hours until adrenal insufficiency is ruled out, as thyroid hormone replacement can precipitate life-threatening adrenal crisis in patients with coexisting adrenal insufficiency. 1, 2

Recommended Thyroid Hormone Regimen

Initial IV Levothyroxine Dosing

• Administer a loading dose of 200-400 mcg levothyroxine IV as the initial treatment in the emergency department. 4, 3
• The IV dose is approximately 50-75% of the oral dose due to higher bioavailability of IV administration. 1
• Continue with daily IV levothyroxine (typically 50-100 mcg IV daily) until the patient can tolerate oral therapy. 1, 3

Addition of Liothyronine for Critically Ill Patients

• For critically ill patients with myxedema coma, add IV liothyronine 5-20 mcg IV every 8-12 hours to the levothyroxine regimen. 5, 4, 3
• The combination of levothyroxine and liothyronine has demonstrated efficacy in treating myxedema coma, with marked improvement in hypothermia and bradycardia following liothyronine introduction. 6, 4
• Continue liothyronine for 5-7 days, then transition to levothyroxine monotherapy. 6, 4

Why Oral Therapy is Inappropriate

• Oral thyroid hormone products (levothyroxine, liothyronine, or desiccated thyroid) should NOT be used initially in myxedema coma due to:
  • Altered mental status preventing reliable oral intake 2, 6
  • Impaired gastrointestinal absorption in severe hypothyroidism 7
  • Need for rapid, reliable hormone delivery in this life-threatening emergency 3
• Some patients remain refractory when transitioned to oral therapy and may require prolonged IV administration. 7

Supportive Care Requirements

• Admit immediately to the intensive care unit for aggressive supportive care. 2
• Maintain airway, breathing, and circulation; intubate if Glasgow Coma Score ≤8. 2
• Treat precipitating factors (infection, trauma, cold exposure, myocardial infarction). 2, 3
• Manage hypothermia with passive rewarming (avoid active rewarming which can cause vasodilation and cardiovascular collapse). 3

Monitoring During Treatment

• Recheck TSH and free T4 every 6-8 weeks during dose titration once stabilized. 1
• For patients with cardiac disease or atrial fibrillation, consider more frequent monitoring within 2 weeks. 1
• Thyroid hormone levels may reach normal range within a few days, but clinical improvement may lag behind laboratory normalization. 4

Common Pitfalls to Avoid

• Never start thyroid hormone before corticosteroids in suspected central hypothyroidism or when adrenal insufficiency cannot be excluded. 1, 2
• Avoid excessive initial dosing in elderly patients (>70 years) or those with cardiovascular disease, as this increases risk for atrial fibrillation, myocardial ischemia, and cardiac decompensation. 1
• Do not rely solely on liothyronine IV monotherapy, as levothyroxine provides the necessary T4 substrate for sustained thyroid hormone effect. 3
• Be prepared for prolonged IV therapy in rare cases where patients fail transition to oral therapy. 7