Long-term neuropsychological sequelae of early-treated congenital hypothyroidism: effects in adolescence

A cohort of over 100 children with congenital hypothyroidism (CH) detected via newborn screening was followed regularly throughout childhood and into adolescence. They were studied using a variety of different tests as part of three consecutive research components: semiannual/annual psychological assessments using age-appropriate intelligence tests (phase I), detailed psychoeducational evaluations in grades 3 and 6 (phase II) and a thorough neuropsychological evaluation during adolescence (phase III). Controls for phase I were siblings and for phase II, classmates and siblings. Phase III controls were drawn from a larger control pool and were individually matched with each CH case for age and gender. The results showed that although the CH group was intellectually functioning well within the normal range by adolescence, the children were performing significantly below expectation. Longitudinal analyses showed significant declines in IQ with age, signifying that the CH group was failing to make the same age-related gains as controls. Children with CH showed significantly poorer performance in visuospatial, language and fine motor areas as well as selective attention and memory deficits. At school, they were initially below par in arithmetic but were able to catch up by grade 6; however, their teachers reported that they were not performing as well as controls in the classroom and they demonstrated more difficulty with more complex school subjects such as science and social studies. Correlational analyses indicated different manifestations of early hypothyroidism versus later treatment factors, suggesting that while some effects can be improved by better treatment and management approaches, others caused by prenatal and perinatal thyroid hormone insufficiency may persist.