Effects of depot growth hormone replacement on thyroid function and volume in adults with congenital isolated growth hormone deficiency.

BACKGROUND: Conflicting data exist on the effects of GH replacement therapy (GHRT) on thyroid function and thyroid volume (TV) in GH-deficient (GHD) patients. AIM: The aim of this study was to assess the effects of GHRT on thyroid function and TV in adults with congenital lifetime isolated GHD (IGHD). SUBJECTS AND METHODS: We studied 20 GH-naïve adults with IGHD due to a homozygous mutation of the GHRH-receptor gene at baseline, after 6-month depot- GH replacement therapy (pGH), and 6-month washout (6mo). Total T(3), free T(4) (FT(4)), reverse T(3) (rT(3)), TSH, IGF-I, SHBG, and TV were measured; body surface area-corrected TV (CTV) was calculated. RESULTS: IGF-I and T(3) increased pGH. T(3) levels remained elevated at 6mo. GHRT did not significantly change FT(4), rT(3), TSH, and SHBG. TV and CTV increased pGH and remained elevated at 6mo. CONCLUSIONS: GHRT in IGHD adults caused an increase in serum T(3) levels and TV, suggesting an important role of the GH-IGF-I axis in thyroid function.