Early detection of congenital hypothyroidism

Congenital hypothyroidism, with an estimated incidence of 1 in 5-10 000 births, is probably the commonest endocrine disorder of early childhood. Its importance lies in the devastating effect which it can have on brain development, leading to subnormality and other manifestations such as clumsiness and hyperactivity. It is common experience that the condition is difficult or impossible to recognize during the first days or weeks after delivery. However, recent advances in laboratory methods, particularly thyrotrophin (TSH) and thyroxine (T4) assays, have opened up the possibility of screening for the disorder before the classical clinical picture develops. Studies on the feasibility of such screening are in progress in several centres. In this issue, Dr. Delange and his colleagues describe their experience at the Saint-Pierre Hospital, Brussels, using a radioimmunoassay to estimate plasma TSH on the 5th day of life. Their results, together with those reported from North America,1-3 clearly indicate that screening for congenital hypothyroidism is technically possible. At first glance, the case for screening for congenital hypothyroidism seems clear. The poor prognosis for cases in which treatment has been very delayed has long been recognized and a number of studies have shown that the outlook is better in patients treated before the age of 3 months. There is less information on the outcome in cases treated soon after birth. In Table 1 we have summarized the available literature on cases treated at or before 6 weeks and on patients in whom treatment started between the ages of 7 and 12 weeks. Again, the results indicate that the prognosis is better with early treatment, particularly with regard to subnormality. While all available evidence indicates that early recognition and treatment of congenital hypothyroidism will reduce the incidence and severity of later handicap, all the published series show wide overlap of intelligence in children treated early and late, and even in cases treated before 6 weeks the proportion with an IQ above 90 is less than expected (Table 1). This variation probably stems from differences in the timing and severity of thyroid deficiency in individual patients. It is widely accepted that the human placenta is impermeable to thyroid hormones but the effect of fetal hypothyroidism on brain growth is less clear. Experiments in animals Table 1 Intelligence in children with congenital hypothyroidism treated before 3 months.*