Correlation between Severity of Growth Hormone Deficiency and Thyroid Metabolism and Effects of Long-Term Growth Hormone Treatment on Thyroid Function in Children with Idiopathic Growth Hormone Deficiency.

BACKGROUND/AIM: The significance of changes in thyroid function in children during growth hormone (GH) treatment remains uncertain. We aimed to evaluate the impact of GH replacement on thyroid status in children with idiopathic GH deficiency (GHD). METHODS: Data of 105 GHD children (82 M, 23 F; aged 11.13 years) during a 36-month follow-up were analyzed. At diagnosis the areas under the curve of GH (AUCGH) were calculated during a GH-releasing hormone + arginine (GHRH-Arg) and insulin tolerance test. RESULTS: A significant ΔfT3 (p < 0.001) was documented at 12 months, without any further change at 24 and 36 months and without fT4 and TSH modifications. Grouping patients according to ΔfT3 at 12 months into those with lower (n = 80, 76%) or greater values than the 75th percentile (n = 25, 24%), the latter showed lower AUCGH and GH peak during a GHRH-Arg (p = 0.018 and 0.014, respectively) and insulin tolerance test (p = 0.023 and 0.020, respectively) at diagnosis. In addition, children with lower GH at diagnosis showed a greater ΔfT3 at 12 months (p = 0.030). CONCLUSIONS: In GHD children, GH treatment is associated with a significant increase in fT3 in the first 12 months, more pronounced in patients with more severe GHD, highlighting the strong correlation between severity of GHD and thyroid metabolism.