Influence of severity of congenital hypothyroidism and adequacy of treatment on school achievement in young adolescents:: a population-based cohort study

Aim: To evaluate whether precociously treated subjects with congenital hypothyroidism (CH) are at risk of poor school performance in early adolescence, and to investigate which factors affect their school achievement. Methods: All children treated early for congenital hypothyroidism and born in France during the first 7 y (1979-1985) of the national screening program for congenital hypothyroidism were selected for the study. School performance during childhood, assessed according to age at entry into the first grade of secondary school, was evaluated as normal (usually 11 y of age) vs late entry (greater than or equal to 12 y). The national register of children with congenital hypothyroidism enabled a comparison to be made with data from the national population for the same school years. Results: School achievement was similar among the 682 patients with CH and in the national population. After an adjustment for the sex and socioprofessional category of the parents, the severity of CH as assessed by the type (athyreosis, the most severe vs other types), the initial low serum T4 levels (less than or equal to 553 nmol/L vs > 53 nmol/L), and the profound bone maturation delay (absence vs presence of the two knee epiphyseal ossification centres at diagnosis), initially low L-thyroxine dosage (below vs greater than or equal to7 mug/kg/day), the absence of near normalization of thyroid hormone levels after 15 d of treatment and poor adequacy of treatment throughout childhood were associated with an increased risk of school delay. School achievement was unaffected by the age at start of treatment (mean age = 22.8 +/- 6.8 d). In a multivariate logistic regression analysis, recurrent episodes of insufficiently suppressed TSH levels 15 mUi/L at least four times during follow-up from the age of 6 mo onwards) were the most important variable associated with school delay. Conclusion: Careful follow-up of the adequacy of treatment is required throughout childhood, to reduce the risk of school delay.