Treatment of Severe Hypothyroidism with TSH 91

A TSH of 91 mIU/L represents severe overt primary hypothyroidism requiring immediate levothyroxine therapy. 1, 2

Immediate Assessment Before Treatment

Confirm the diagnosis by measuring both TSH and free T4 to distinguish overt hypothyroidism (low free T4) from the unlikely scenario of laboratory error, as TSH >10 mIU/L with low free T4 definitively indicates overt hypothyroidism requiring treatment. 1
Rule out adrenal insufficiency first, especially if there are any signs of central hypothyroidism or hypopituitarism, because starting levothyroxine before corticosteroids can precipitate life-threatening adrenal crisis. 1
Assess cardiac status including history of coronary artery disease, atrial fibrillation, heart failure, or age >70 years, as this determines starting dose and titration speed. 1, 2, 3

For patients <70 years without cardiac disease:

Start with full replacement dose of 1.6 mcg/kg/day based on ideal body weight. 1, 2, 3
This aggressive approach is safe in young, healthy patients and achieves euthyroid state faster. 2

For patients >70 years OR with cardiac disease (coronary artery disease, atrial fibrillation, heart failure):

Start with 25-50 mcg/day to avoid precipitating cardiac decompensation, angina, or arrhythmias. 1, 2, 3, 4
Elderly patients with underlying coronary disease are at increased risk of cardiac complications even with therapeutic levothyroxine doses. 4

Take levothyroxine on an empty stomach, 30-60 minutes before breakfast with a full glass of water. 3
Separate from iron and calcium supplements by at least 4 hours, as these interfere with absorption. 2, 3
Avoid administration with foods that decrease absorption, particularly soybean-based products. 3

Recheck TSH and free T4 in 6-8 weeks after starting therapy or any dose change, as peak therapeutic effect takes 4-6 weeks. 1, 3, 4
Adjust dose by 12.5-25 mcg increments every 6-8 weeks until TSH normalizes to 0.5-4.5 mIU/L. 1, 3
For patients with cardiac disease, titrate more slowly every 6-8 weeks rather than every 4-6 weeks. 3
Target TSH: 0.5-4.5 mIU/L with normal free T4 levels. 1, 4

At this severity level (TSH 91), the patient likely has symptomatic hypothyroidism with fatigue (68-83%), weight gain (24-59%), cognitive issues (45-48%), and menstrual irregularities (23%). 4
Risk of myxedema coma exists with untreated severe hypothyroidism, which has 30% mortality and requires ICU management. 4
This level of TSH elevation indicates long-standing, severe thyroid failure requiring careful monitoring during initial treatment. 4

Every 6-8 weeks during dose titration until TSH normalizes. 1, 3
Every 6-12 months once stable on maintenance dose. 1
More frequently (within 2 weeks) if cardiac disease, atrial fibrillation, or serious medical conditions are present. 1

Never start with full replacement dose in elderly or cardiac patients, as this can precipitate myocardial infarction, heart failure, or atrial fibrillation. 1, 2, 4
Do not adjust doses more frequently than every 6-8 weeks, as steady state is not reached before this time. 1, 3
Avoid overtreatment, which occurs in 14-21% of patients and increases risk for atrial fibrillation, osteoporosis, fractures, and cardiac complications. 1
Do not treat based on single TSH value alone - confirm with free T4 measurement, though at TSH 91 this is almost certainly true hypothyroidism. 1
Never start levothyroxine before ruling out adrenal insufficiency in patients with suspected central causes or hypopituitarism. 1

Symptom improvement typically begins within 2-4 weeks but full therapeutic effect takes 4-6 weeks. 3
TSH normalization usually requires 3-6 months of dose adjustments. 1
Lifelong therapy is required for chronic primary hypothyroidism, with annual monitoring once stable. 1, 4