Background: Normal thyroid function is necessary for the optimal growth promoting effects of GH. Changes in the hypothalamic-pituitary-thyroid (HPT) axis following GH have been reported in subjects initially thought to be euthyroid. A specific group of patients, children with Prader-Willi syndrome (PWS), are thought to have a vulnerable HPT axis.
Objective and hypotheses: To evaluate the impact of paediatric GH therapy on thyroid hormone status, with a particular interest in children with PWS. We hypothesised that GH in PWS children would result in hypothyroidism that is central in origin.
Method: 137 and 147 test encounters for fT4 or TSH respectively, were analysed from the OZGROW database, prior to and during GH, for individuals who were receiving GH therapy since 2009. Where a reference range was provided, fT4 or TSH was standardized by expressing them as a % of the given reference range. We did a general analysis and a comparative analysis of individual patients test results (where available) before GH and afterwards.
Results: 16 and 13 encounters of fT4 and TSH respectively had tests before GH and within a year afterwards. Of these, 12 and ten patients respectively had PWS. Overall there was no significant difference in fT4 or TSH results after GH was commenced (P=0.98 for fT4 and P=0.24 for TSH). However, for PWS patients there was a significant reduction in median TSH results after GH commencement using standardised % reference ranges (32.17% before to 25% after, P=0.01). There was also a significant decrease in TSH within 12 PWS patients who had both before and after tests (paired t-test P=0.002); there was however no evidence of a reduction in fT4 in these patients. Of note four of these PWS patients in the latter group had been treated with thyroxine.
Conclusion: This study showed that overall there was no significant change in TSH and T4 levels post GH therapy. However, PWS patients showed a significant decrease in TSH levels, where GH therapy may unmask a state of central hypothyroidism. Whether these changes in TSH were clinically significant, remains unclear.
01 Oct 2015 - 03 Oct 2015