ESPE Abstracts

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 Children’s 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.