Central hypothyroidism after starting Growth Hormone Treatment; the unmasking of mild congenital hypothyroidism?

INTRODUCTION After starting growth hormone (GH) treatment for ‘isolated’ growth hormone (GH) defi ciency (GHD), the free thyroxine (FT4) concentration may fall. We hypothesize that this fall in FT4 is the unmasking of a mild central congenital hypothyroidism, indicating the existence of Multiple Pituitary Hormone Defi ciency (MPHD) and not isolated GHD.The goal of our study was to compare the T4 concentration at time of neonatal screening between children with ‘true’ isolated GHD compared to children developing hypothyroxinemia after starting GH treatment.