ESPE Yearbook of Paediatric Endocrinology

Eur J Endocrinol 2024 Aug 5;191(2):126-133.PMID: 39049789. doi: 10.1093/ejendo/lvae088

Brief Summary: This study investigated thyroid function during growth hormone (GH) treatment in children with Prader-Willi syndrome (PWS), using data from a 2-year randomized controlled trial (RCT) and a 10-year longitudinal GH study.

GH treatment led to a significant decrease in serum free T4 (FT4) levels and an increase in T3 levels, suggesting increased peripheral conversion of FT4 to T3. This was observed in both the 2-year RCT and the larger 10-year longitudinal study. In contrast, FT4 and T3 levels remained largely unchanged in untreated controls. After the initial changes, FT4 and T3 levels normalized and remained stable within the normal range during long-term GH treatment (between 2 and 10 years) in almost all children with PWS. Regarding TSH levels, TSH SDS generally decreased over the long term but remained within the normal range. True hypothyroidism was very rare in children with PWS. Even when FT4 levels were occasionally low (below -2 SDS), TSH levels were typically normal, and T3 levels were almost always normal. In some cases, thyroxin replacement therapy was initiated based solely on low FT4, but T3 and TSH levels were normal, and subsequent normalization of thyroid hormones occurred upon cessation of thyroxin.

Based on these findings, the authors recommend measuring T3 levels when FT4 is low in children with PWS, especially during the first months of GH treatment, to avoid unnecessary thyroxin replacement.