Head circumference and linear growth during the first 3 years in treated congenital hypothyroidism in relation to aetiology and initial biochemical severity.

AIMS

To determine the head circumference and linear growth in children with congenital hypothyroidism (CH) during the first 3 years of life in relation to the aetiology of CH and initial biochemical severity of thyroid function.

METHODS

We examined the head circumference and linear growth of 125 patients with CH from diagnosis up to 3 years of age. All infants had radionuclide scans prior to treatment. Patients were categorized into athyreosis, ectopia and dyshormonogenesis. Occipito-frontal circumference (OFC) SD, length SD, initial plasma TSH, initial plasma thyroxine (T4) and age of suppression of plasma TSH were compared between the groups. Multiple linear regression analysis was used to determine factors affecting OFC SD at 3 years of age.

RESULTS

There were 125 children in the study: athyreosis (n = 34), ectopia (n = 73) and dyshormonogenesis (n = 18). No difference was found in gestation, birth weight, age of starting L-T4 and initial dose of L-T4 in mcg/kg/day between groups. Confirmatory plasma total T4 at diagnosis was significantly lower for athyreosis when compared with ectopia and dyshormonogenesis. Median values for confirmatory TSH were significantly lower in dyshormonogenesis compared with the other two groups. At diagnosis, OFC were similar in all three groups. Children with athyreosis showed significantly larger OFCs compared with ectopia and dyshormonogenesis from 1 to 3 years. Length SD was within 1 SD of normal population standards at diagnosis and did not differ between the three groups throughout the 3 years. Spearman's correlation for OFC SD at 3 years of age showed a significant negative correlation with initial confirmatory plasma T4 (r = -0.35, P = 0.01). Multivariate analysis for OFC SD at 3 years of age showed confirmatory T4 as the only independent risk factor.

CONCLUSION

Children with athyreosis showed significantly larger OFC from 1 to 3 years of age compared with ectopia and dyshormonogenesis, independent of linear growth. Our data shows that initial confirmatory T4 at diagnosis is an independent factor influencing head growth in the first 3 years of life.