Background: Normal thyroid function is necessary for the optimal effect of recombinant growth hormone (rhGH) on growth rate. GH therapy in children with GH deficiency (GHD) has yielded conflicting results concerning its impact on thyroid function. Data about patients developing subclinical hypothyroidism (SH) are scanty, but it is thought to be associated with impairment of metabolic profile and lower growth response.
Objective: To evaluate the effect of rhGH administration on TSH tertiles and FT4, the frequency of SH, as well as to assess its influence on therapy effectiveness.
Method: We reviewed the cases of 75 children (59 boys, 16 girls, aged 4−14) with pituitary dwarfism. Clinical and hormonal data, as well as radiographic bone assessments were documented at the beginning, 6 months and after first year of treatment.
Results: At therapy onset, all patients had the height below −2.5 SD (mean −3.2), delayed bone age, decreased or low normal IGF1 and normal thyroid function. After one year of therapy, SH was the only impairment in thyroid function in 12 patients (16%). The risk of SH was increased among subjects with the highest tertile TSH as compared with subjects with the lowest tertile (P<0.05). Despite similar IGF1 secretion increase, the improvement of height velocity was significantly lower in children with SH (0.65 cm/month) than in those who remained euthyroid (0.88 cm/month, P<0.05). An increase in IGF1 levels was associated with increasing levels of TSH in SH patients and led in four cases to administration of L−T4 substitution.
Conclusion: The incidence of SH during the first year of rhGH treatment in children with GHD and the influence on the growth rate should be taken into account, as it may worsen the growth response. Our findings suggest that suboptimal thyroid function increases vulnerability to the occurrence of SH in children treated with rhGH, needing a closer monitoring.