Effects of levothyroxine on growth hormone (gh) sensitivity in children with idiopathic short stature

BackgroundThe possible relationship between the circulating concentrations of T4 and GH sensitivity has not been elucidated.ObjectiveThe aim of this study is to evaluate the effect of levothyroxine supplementation on GH sensitivity in prepubertal boys with idiopathic short stature (ISS).MethodsWe selected 28 prepubertal boys with ISS (mean age 8.2 ± 0.5 years) and free T4 (Ft4) concentrations between the 3rd and the 25th percentiles (Ft4: 0.8–1.5 ng/dl). They were randomly divided into two groups: Group A received thyroid supplementation (1–3 μg/kg/day) for 120 days, and Group B received placebo for the same period. To evaluate GH sensitivity, an IGF-I generation test (GH: 33 μg/kg/day sc for 3 days) was performed in both groups: under basal conditions, and after 120 days of levothyroxine supplementation (or placebo).ResultsAfter thyroid supplementation, Group A had higher Ft4 concentrations compared with Group B (2.14 ± 0.06 vs 1.48 ± 0.06 ng/dl, p = 0.01), their growth velocity was significantly higher (2.3 ± 0.1 vs 1.5 ± 0.2 cm/4 months), and they exhibited a greater increase in IGF-I after GH administration (Group A: 32.5 ± 3.8% vs Group B 17.3 ± 2.6%).ConclusionSupplementation with levothyroxine for 120 days promotes an increase in growth velocity, and a greater IGF-I response to short-term GH administration in prepubertal boys with ISS and low-normal thyroid hormone concentrations.