Intellectual development at 10 years in early treated congenital hypothyroidism.

Fifty nine children born between 1978 and 1981 with congenital hypothyroidism detected by neonatal screening were assessed at 10 years using the Wechsler intelligence scale for children, together with 59 matched classroom controls. Thirty one children with severe hypothyroidism who had pretreatment plasma thyroxine concentrations of 40 nmol/l or less had a mean (SD) full scale IQ score of 104.7 (15.1), compared with a mean (SD) score of 114.6 (16.3) for the 28 less severely affected children who had pretreatment thyroxine levels greater than 40 nmol/l, and mean (SD) scores of 114.5 (12.8) and 114.8 (13.8) respectively for the 31 and 28 control children. In the hypothyroid children the IQ scores at 10 years were closely related to the IQ scores at 5 years and at 3 years. It is concluded that the deficit in IQ score found at 3 and 5 years in children with severe hypothyroidism is still evident at the age of 10 years.