[Effect of treatment with biosynthetic GH on thyroid function in patients with an isolated deficiency of GH]

The use of GH treatment in subjects with a GH deficiency has led to contrasting results concerning its impact to develop thyroid hyperfunction, whereas many others have underlined the possible onset of hypothyroidism. A number of studies have been carried out over short periods in subjects with multiple tropin deficiencies, in healthy adults or adults with GH deficiencies, in healthy adults or adults with GH deficiencies. The aim of the present study was to assess the effect of prolonged treatment with biosynthetic GH on thyroid function in children with an isolated idiopathic GH deficiency. The study included 8 children (mean age 10.4 +/- 0.8 years) with GH deficiencies treated with biosynthetic GH and 8 children with familial retarded stature of a similar age (mean age 10.3 +/- 0.7 years) who represented the control group. Serum levels of T3, T4, FT3, FT4 and TSH were measured at the start of the study and after one year of continuous GH treatment in subjects with GH deficiency; the same tests were performed in the control group on recruitment and after one year's observation without therapy. T4 and FT4 levels diminished, but not significantly, whereas there was a significant increase in plasma levels of T3 and FT3 (p less than 0.01); TSH values were significantly reduced in the treated group (p = 0.025). No significant variations in thyroid parameters were found in the control group. These data support the hypothesis of an increased peripheral conversion of T4 into T3 due to GH therapy; in conclusion, however, no significant variation in thyroid function was observed following GH replacement therapy, even if prolonged, in subjects with an idiopathic isolated GH deficiency.