Characteristics of infantile hypothyroidism discovered on neonatal screening

Abstract

Clinical and laboratory data from 146 patients with infantile hypothyroidism diagnosed by neonatal screening over a five-year period are presented. In 95 patients there was adequate thyroid imaging or evidence of dyshormonogenesis; of these, 43% had ectopic thyroid tissue, 22% had goitrous hypothyroidism, and 35% had hypoplastic or aplastic glands. Stanford-Binet IQs of the patients at 3, 4, and 5 years of age were identical with those of control subjects. Patients in whom thyroid tissue was demonstrable on radioactive scanning had higher concentrations of T4 and T3, and lower concentrations of TSH and less retarded bone age, but did not differ in ultimate IQ from patients with no demonstrable thyroid tissue. No significant correlation with ultimate IQ was found for any clinical or laboratory factor except for the adequacy of treatment. Eleven children with inadequate treatment had a mean IQ significantly less than that of other patients, 87 +/- 5 (SEM) vs 105 +/- 2. Inadequate treatment was defined essentially by repeated T4 concentrations less than 8 micrograms/dl during treatment. Thus, T4 values in the lower part of the normal range are probably incompatible with maximal intellectual development, and every effort should be exerted to maintain serum T4 levels in the upper half of the normal range during the first year of life.