Intellectual outcome of patients with congenital hypothyroidism detected by neonatal screening

Mental retardation is a major sequela of delayed treatment for congenital hypothyroidism; congenital hypothyroidism can be treated early if detected with neonatal screening. We evaluated the intellectual outcomes of 62 patients with congenital hypothyroidism detected by neonatal screening at a major teaching hospital in northern Taiwan. The effects of thyroid pathology, age at the initiation of treatment, socioeconomic status, and severity of hypothyroidism on intellectual outcome were also analyzed.

All patients had euthyroid status at the time of intelligence testing. The Chinese Fourth Revision of the Binet-Simon Scales was used to evaluate the patients' intelligence between the ages of 3 and 6 years.

The mean intelligence quotient (IQ) score was 102 +/- 18. Only four of the 62 patients were mentally retarded. Patients with lower initial serum thyroxine concentrations (T4; < 2 micrograms/dL) at the time of diagnosis of congenital hypothyroidism had significantly lower IQs (95 +/- 19, n = 26) than those with higher initial T4 concentrations (106 +/- 16, n = 36; p < 0.05). Patients with fewer than three ossification centers had lower IQs (91 +/- 20, n = 12) than those with three or more (104 +/- 17, n = 36; p < 0.05). Significantly lower IQs were also found in patients with a smaller femoral epiphysis area (< 0.1 cm2) (92 +/- 20, n = 15) than in those with larger epiphyses (106 +/- 15, n = 21; p < 0.05). The type of pathology (ectopia, athyrosis, dyshormonogenesis), age at the start of treatment (before or after 30 days of age), and socioeconomic status did not significantly affect the intellectual outcome.

Our results indicate that intellectual outcome in Taiwanese patients with congenital hypothyroidism has been improved by neonatal screening and that the severity of hypothyroidism at diagnosis is the most important prognostic factor affecting intellectual outcome in these patients.