LONG-TERM EFFECTS OF L-THYROXINE THERAPY FOR CONGENITAL HYPOTHYROIDISM

Objective: To study the effects of initial and concurrent dose levels of L-thyroxine on ability and behavior in children with congenital hyp othyroidism. Methods: An existing database, involving a large cohort o f children with congenital hypothyroidism detected by neonatal screeni ng, was analyzed retrospectively, There were 94 children: 89 were asse ssed at age 7 years for intelligence and selective cognitive abilities , and 87 at age 8 years for behavior, achievement, and selective abili ties. Results: Subjects were stratified by median spilt into low and h igh starting dose groups. The high-dose group performed better on inde xes of intelligence, verbal ability, and memory but had more behavior problems reflecting increased anxiety, social withdrawal, and poorer c oncentration. The dose of L-thyroxine at age 8 years was negatively co rrelated with memory task performance. Conclusion: A higher starting d ose of L-thyroxine is beneficial for subsequent intellectual outcome i n children with congenital hypothyroidism but may be associated with i nternalizing behavior problems.