Longitudinal assessment of L-T4 therapy for congenital hypothyroidism: differences between athyreosis vs ectopia and delayed vs normal bone age.

Abstract

To study the effects of LT4 dose on thyroid hormone serum levels, a prospective, longitudinal and comparative study was designed, including 56 term eutrophic 1-89 day-old infants with congenital hypothyroidism (CH) detected by neonatal screening. Patients were divided into four groups according to delayed or normal bone age at birth, and athyreosis or ectopic thyroid. All received an initial dose of 50 micrograms/day (12.9-13.7 micrograms/kg/day) LT4 and were followed bimonthly (first year) and quarterly (second year) with thyroid profile and bone age determinations at 6, 12 and 24 months. At diagnosis, hormone levels were higher in cases of ectopia than in athyreosis (p < 0.001), and T4 was lower in children with delayed than in normal bone age at birth (p < 0.05). During treatment, all groups were clinically euthyroid despite T4 and FT4 serum levels higher than the upper normal limit (p < 0.0.001), though T3 and FT3 were within the normal limit (p > 0.05). TSH normalized within 8 weeks. Bone age accelerated at 2 years in eight children of the bone age delayed group. No patient had craniosynostosis.