Effect of hypothyroidism and its treatment on the IGF system in infants and children.

We performed a study on infants and children with hypothyroidism to determine the effect of hypothyroidism and its correction on components of the IGF system. A total of 35 patients were subdivided into four groups based on age and severity of the disease. Serum concentrations of immunoreactive IGF-I, free IGF-I, IGFBP-2 and IGFBP-3 were measured before and after treatment and compared to controls matched for age, sex and puberty. Baseline total IGF-I (TIGF-I) concentrations were significantly lower prior to treatment in the infants with severe hypothyroidism and increased significantly after thyroxine therapy. Baseline free IGF-I (FIGF-I) concentration was significantly lower prior to treatment in infants with severe hypothyroidism when compared to controls but did not increase significantly after treatment. In infants with severe and compensated hypothyroidism, IGFBP-3 concentrations prior to treatment were lower when compared to controls. These concentrations increased during treatment. Baseline IGFBP-2 levels did not differ from the control values in both these groups but decreased significantly after correction of the hypothyroidism. Although these changes appeared to occur with thyroxine therapy, multiple regression analysis suggested that age was a more important determinant of the changes observed in these parameters than serum thyroxine concentration. In children with acquired hypothyroidism no difference in any of these parameters was noted between hypothyroid patients and controls. TIGF-I increased significantly on thyroxine therapy, but the difference was small. No significant differences were noted in other measured parameters with thyroxine therapy. In older children with compensated hypothyroidism no significant differences were noted in any of the measured parameters in the pretreatment, post-treatment and control groups. In conclusion, although changes appear in TIGF-I, IGFBP-3 and IGFBP-2 in infants with congenital hypothyroidism when they are treated with thyroxine, age appears to be the more important determinant of these changes than does thyroxine concentration. In older children with acquired hypothyroidism, TIGF-I and FIGF-I levels were not significantly lower than in age- and sex-matched controls. After treatment only TIGF-I levels increased.