Abstract
Background: Hypothyroidism in children leads to growth retardation. However, there is some evidence that recombinant human growth hormone (rhGH) therapy could suppress thyroid function. The most common observation in rhGH-treated patients is a decrease in thyroxine levels, which is reported as transient, but the studies in the field are inconsistent. We aimed to evaluate thyroid function in initially euthyroid children with idiopathic isolated GH deficiency during long-term rhGH therapy and to determine who is at a higher risk of thyroid function alterations during the therapy. Methods: The study group consisted of 101 children treated with rhGH for at least three years. Serum TSH and fT4 levels were determined at baseline, after the first six months and after each full year of therapy. The associations between changes in thyroid hormone levels during rhGH therapy and GH deficit, insulin-like growth factor-1 levels and growth response were investigated. Results: A significant decrease in fT4 levels (p = 0.01) was found as early as after the first six months of rhGH therapy. This effect persisted in the subsequent years of treatment without any significant changes in TSH values and tended to be rhGH dose related. Children with a greater fT4 decrease after the initiation of rhGH therapy were older, had higher bone age and responded to that therapy worse than children with lower fT4 changes. Conclusions: Our study revealed a long-term decrease in fT4 levels during rhGH therapy in initially euthyroid GHD children. The decrease in fT4 levels was associated with a lower growth response to rhGH therapy.
Highlights
One of the main symptoms of hypothyroidism in children, irrespective of its etiology, is growth impairment
We found that children with a good growth response to recombinant human growth hormone (rhGH) therapy had lower fT4 reduction during treatment
Our results indicate that rhGH therapy in GH-deficient initially euthyroid children affects thyroid function, especially fT4 levels
Summary
One of the main symptoms of hypothyroidism in children, irrespective of its etiology, is growth impairment. The most common finding in patients treated with rhGH is a significant decrease in free thyroxine (fT4) levels, which is considered as transient and observed mainly in the first year of therapy [16,18,21,27]. In GH-deficient children, a persistent decrease in fT4 levels due to rhGH therapy could result in a significant reduction in height velocity (HV) and, in deterioration of the growth response to the treatment. In those cases, levothyroxine (L-thyroxine) supplementation should be taken into account as a possible way to achieve the optimal growth effect of rhGH therapy [27]. The associations between changes in thyroid hormone levels during rhGH therapy and GH deficit, insulin-like growth factor-1 levels and growth response were investigated
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