What is the diagnosis and treatment for an elderly female patient with severe hypothyroidism, as indicated by elevated Thyroid-Stimulating Hormone (TSH) levels, low Triiodothyronine (T3) and Thyroxine (T4) levels?

Severe Primary Hypothyroidism (Myxedema)

Diagnosis

This elderly female patient has severe overt primary hypothyroidism (myxedema) based on markedly elevated TSH (135 mIU/L) with profoundly suppressed T3 (<0.3) and T4 (<0.10). 1, 2

The constellation of extremely elevated TSH with undetectable thyroid hormones confirms primary thyroid gland failure, most likely from autoimmune thyroiditis (Hashimoto's disease) given the patient's age and sex 2, 3. This represents a medical emergency requiring immediate treatment, as severe untreated hypothyroidism can progress to myxedema coma, heart failure, psychosis, and death 2, 4.

Critical Pre-Treatment Safety Assessment

Before initiating any levothyroxine, you must rule out concurrent adrenal insufficiency, as starting thyroid hormone before corticosteroids can precipitate life-threatening adrenal crisis. 1, 5

• Check morning cortisol and ACTH levels immediately 1
• If adrenal insufficiency is present or suspected, start physiologic dose steroids (hydrocortisone 15-20 mg daily) at least 1 week prior to thyroid hormone replacement 1, 6
• In autoimmune hypothyroidism, there is increased risk of concurrent autoimmune adrenal insufficiency (Addison's disease) 1

Treatment Protocol for Elderly Patients

Initial Levothyroxine Dosing

For this elderly patient, start with 25-50 mcg levothyroxine daily, NOT full replacement dose. 1, 5, 3

• The standard full replacement dose of 1.6 mcg/kg/day is contraindicated in elderly patients 1, 5
• Starting at 25 mcg daily is safest for patients over 70 years 1, 3
• Elderly patients with underlying coronary disease are at increased risk of cardiac decompensation, angina, or arrhythmias even with therapeutic levothyroxine doses 1, 3
• Rapid normalization can unmask or worsen cardiac ischemia, precipitate myocardial infarction, heart failure, or fatal arrhythmias 1, 4

Titration Strategy

Increase levothyroxine by 12.5-25 mcg every 6-8 weeks based on TSH response. 1, 5

• Recheck TSH and free T4 at 6-8 week intervals after each dose adjustment 1, 5
• Use smaller increments (12.5 mcg) in very elderly patients or those with cardiac disease 1
• Target TSH range is 0.5-4.5 mIU/L, though slightly higher targets (up to 5-6 mIU/L) may be acceptable in very elderly patients to avoid overtreatment risks 1
• Monitor closely for angina, palpitations, dyspnea, or arrhythmias at each follow-up 1
• Obtain ECG to screen for baseline arrhythmias before treatment 1

Long-Term Monitoring

Once TSH stabilizes in target range, monitor TSH every 6-12 months or sooner if symptoms change. 1, 5

• Annual monitoring is sufficient for stable patients on consistent dose 1
• Free T4 can help interpret ongoing abnormal TSH levels during therapy, as TSH may take longer to normalize 1

Critical Pitfalls to Avoid

Never start at full replacement dose in elderly patients—this can precipitate myocardial infarction, heart failure, or fatal arrhythmias. 1, 3

• Approximately 25% of patients on levothyroxine are unintentionally maintained on doses sufficient to fully suppress TSH, increasing risks for atrial fibrillation, osteoporosis, fractures, and cardiac complications 1
• Adjusting doses too frequently before reaching steady state (must wait 6-8 weeks between adjustments) leads to inappropriate dosing 1
• Never assume hypothyroidism is permanent without reassessment—consider transient thyroiditis, though with TSH this elevated, permanent hypothyroidism is most likely 1
• Failure to rule out adrenal insufficiency before starting levothyroxine can cause adrenal crisis 1, 5

Expected Recovery Timeline

Recovery and stabilization may take 6-8 months in elderly patients with severe hypothyroidism. 4

• Symptoms should begin improving within 6-8 weeks of adequate levothyroxine replacement 1
• Full normalization of TSH may require multiple dose adjustments over several months 3, 4
• Cardiovascular function improves with treatment, reducing risk of heart failure and adverse lipid profiles 1

Special Considerations for Severe Hypothyroidism

This patient requires close monitoring for myxedema coma, which occurs primarily in elderly women and requires immediate treatment to prevent death. 4

• Signs include hypothermia, altered mental status, hypotension, hypoventilation, and hyponatremia 2, 4
• If myxedema coma is suspected, this becomes an ICU-level emergency requiring IV levothyroxine and supportive care 4
• Ensure adequate calcium (1200 mg/day) and vitamin D (1000 units/day) intake to prevent bone demineralization during treatment 1