Background: Recent guidelines recommend levothyroxine (LT4) monotherapy for all infants with congenital hypothyroidism (CH). However, up to one-third of patients have pituitary resistance to thyroid hormone and, to normalize their TSH, require supranormal circulating levels of T4. Liothyronine (T3) has been proposed as a supplemental therapy for such patients, but data demonstrating its use and efficacy are limited.
Objective and hypotheses: Through a retrospective chart review we sought to test the hypothesis that supplemental T3 treatment will decrease both TSH and T4 in patients with CH and pituitary resistance to thyroid hormone.
Method: We studied all CH patients seen at Boston Childrens Hospital from 99-present who were treated with T3 for pituitary resistance and who were compliant with therapy.All patients were treated with LT4, and T3 was added because of failure to normalize TSH. We used paired t-tests to compare serum TSH, free T4 or total T4 and T3 during the 2 years before vs 2 years after starting T3 treatment.
Results: We identified six patients (four males, two females) treated with combined LT4 and T3. Patients started T3 therapy at a median initial dose of 0.29 μg/kg per day divided once or twice daily, with a median decrease in LT4 dose by 11%. T3 treatment was associated with lower average TSH (9.2 vs 4.5 mIU/l) and a decrease of TSH values>10 mIU/l. Area under the curve of fT4 or total T4 decreased by 23±9% after T3 treatment. The proportion of serum T3 values above normal tended to increase during T3 treatment.
Conclusion: Addition of T3 to LT4 monotherapy is associated with lower serum TSH and T4 in CH patients with pituitary resistance to thyroid hormone. Larger prospective studies are needed to validate these findings and to investigate whether the addition of T3 improves cognitive development.
01 Oct 2015 - 03 Oct 2015