Neonatal hypothyroidism: Treatment and outcome

Systematic neonatal screening for congenital hypothyroidism (CH), which was progressively implemented in industrialized countries over the past 15 to 25 years, has been extremely successful in eradicating severe mental defici ency resulting from CH. However, in the first generation of children diagno sed by screening, the concept that CH has a threshold effect on intelligenc e was confirmed. In spite of earlier diagnosis through screening, children with severe CH (ie, those with a marked retardation of bone age and/or a lo w circulating thyroxine [T-4] before treatment) still had clinically signif icant intellectual sequelae, amounting to a loss of 6 to 19 IQ points. Rece nt studies suggest that this developmental gap may be closed by treating mo re rapidly after birth (2 weeks instead of 4-5 weeks in the early years of the screening era) and by using a higher initial dose of levothyroxine (10- 15 instead of 5-8 mu g/kg per day). This regimen induces transient hyperthy roxinemia, but no clinical signs or symptoms of hyperthyroidism. Longer ter m follow-up of larger numbers of patients remains necessary to confirm the normalization of intellectual development and the absence of untowards effe cts of the treatment regimen in children with severe CH.