Intellectual outcomes of patients with congenital hypothyroidism not detected by neonatal screening

Mental retardation is a major sequela of delayed treatment of congenital hypothyroidism. In this study, we investigated the intellectual outcomes of patients with congenital hypothyroidism diagnosed before a nationwide screening project started, Eight-two patients had intelligence tests done while in the euthyroid state, Their mean intelligence quotient (IQ) was 78 +/- 21 (+/- SD) (n = 79). The mean verbal IQ was significantly higher than the mean full-scale IQ. The mean IQs of both ectopic thyroid (84 +/- 21, n = 28) and dyshormonogenic patients (85 +/- 14, n = 18) were significantly higher than that of patients with athyrosis (64 +/- 18, n = 19) (p < 0.05). Patients who were treated before 3 months of age had significantly higher mean IQs (90 +/- 16, n = 16) than those treated after 3 months (75 +/- 21, n = 63) (p < 0.01). Our results confirm that both patients with ectopic thyroids and those with dyshormonogenesis have better intellectual outcomes than athyrotic patients do, and that early treatment improves the intellectual outcome of patients with congenital hypothyroidism.