Treatment of Myxedema
Critical Distinction: Myxedema vs. Myxedema Coma
For stable myxedema (severe hypothyroidism without life-threatening decompensation), initiate oral levothyroxine at 1.5-1.8 mcg/kg/day in younger patients without cardiac disease, but use significantly lower starting doses (25-50 mcg daily) in elderly patients or those with known/suspected cardiac disease to avoid precipitating cardiovascular complications. 1, 2
However, oral thyroid hormone products are NOT recommended for myxedema coma—intravenous formulations must be used for this life-threatening emergency. 3
Treatment Algorithm for Stable Myxedema
Initial Dosing Strategy
Younger patients (<60 years) without cardiac disease: Start levothyroxine at 1.5-1.8 mcg/kg/day 2
Elderly patients (≥60 years) or those with known/suspected ischemic heart disease: Start at 12.5-50 mcg daily and titrate gradually to avoid angina, arrhythmias, or increased cardiac wall thickness 1, 3, 2
The narrow therapeutic index of levothyroxine means both overtreatment and undertreatment carry significant risks affecting cardiovascular function, bone metabolism, and cognitive function 3
Monitoring and Titration
Check TSH levels every 6-8 weeks while titrating to achieve TSH within the reference range 1
The typical maintenance dose is 1.6 mcg/kg/day for patients without risk factors 1
Monitor for cardiac arrhythmias, particularly in patients with coronary artery disease 3
Critical Precautions Before Starting Treatment
Rule out adrenal insufficiency first: Thyroid hormone increases metabolic clearance of glucocorticoids, and initiating levothyroxine before glucocorticoid replacement can precipitate acute adrenal crisis 1, 3
Diabetic patients: Levothyroxine may worsen glycemic control, requiring increased antidiabetic medications or insulin 3
Treatment of Myxedema Coma
Immediate Management
Myxedema coma requires immediate ICU admission with aggressive supportive care, including intubation if Glasgow Coma Score ≤8, and intravenous thyroid hormone administration—oral formulations are contraindicated due to unpredictable gastrointestinal absorption. 1, 3
Thyroid Hormone Replacement in Myxedema Coma
Intravenous levothyroxine is the recommended route per FDA labeling, as oral absorption is unpredictable in this critically ill state 3
Some evidence supports combination therapy with both levothyroxine and liothyronine (T3) for faster normalization of thyroid hormone levels 4, 5
If IV formulations are unavailable (resource-limited settings), oral levothyroxine at loading doses of 300-500 mcg followed by taper over 3-5 days has shown effectiveness, though this contradicts FDA guidance 6
Essential Concurrent Therapies
Administer hydrocortisone 100 mg IV every 8 hours until adrenal insufficiency is ruled out, as thyroid hormone replacement can unmask or worsen adrenal crisis 1
Correct hypoglycemia immediately if present 1
Maintain airway, breathing, and circulation with mechanical ventilation as needed 1
Common Pitfalls
Starting full replacement doses in elderly or cardiac patients: This can precipitate angina, arrhythmias, or myocardial infarction—always start low (25-50 mcg) and go slow in these populations 1, 3, 2
Initiating thyroid hormone before addressing adrenal insufficiency: This is a potentially fatal error that can trigger adrenal crisis 1, 3
Using oral levothyroxine for myxedema coma: The FDA explicitly warns against this due to poor circulation and unpredictable absorption 3
Over-replacement leading to bone loss: Particularly concerning in postmenopausal women, as excess thyroid hormone increases bone resorption and decreases bone mineral density 3