Skeletal maturation during thyroxine treatment in children with congenital hypothyroidism.

The aim of this investigation was to study if bone age development (assessed by the Greulich & Pyle atlas) was related to L-thyroxine treatment in 47 children with congenital hypothyroidism, treated early and according to general recommendations. In spite of frequent delay in skeletal maturation at diagnosis, the delay in mean bone age at a mean chronological age of 1.5 years was slight (0.5 months), and 30% of the variation in bone age SD score (SDS) at 1.5 years was accounted for by the dose of L-thyroxine and serum thyroxine during the first year. The children with a bone age within +/- 1 SDS had a prescribed mean dose of L-thyroxine per kg body weight from 3 to 12 months of age of 5.4 +/- 1.7 micrograms/kg/day, and their mean serum thyroxine concentration during the first year was 175 +/- 29 nmol/l. We conclude that bone age at 1.5 years of age was positively correlated with the dose of L-thyroxine and the serum thyroxine concentrations during the first year. This supports the general use of bone age assessments as a complement to other treatment variables in the follow-up of children with congenital hypothyroidism.