ESPE Abstracts

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.