Long-term effects of L-thyroxine therapy for congenital hypothyroidism,☆☆,,★★

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Abstract

Objective: To study the effects of initial and concurrent dose levels of L-thyroxine on ability and behavior in children with congenital hypothyroidism. Methods: An existing database, involving a large cohort of children with congenital hypothyroidism detected by neonatal screening, was analyzed retrospectively. There were 94 children: 89 were assessed at age 7 years for intelligence and selective cognitive abilities, and 87 at age 8 years for behavior, achievement, and selective abilities. Results: Subjects were stratified by median split into low and high starting dose groups. The high-dose group performed better on indexes of intelligence, verbal ability, and memory but had more behavior problems reflecting increased anxiety, social withdrawal, and poorer concentration. The dose of l-thyroxine at age 8 years was negatively correlated with memory task performance. Conclusion: A higher starting dose of L-thyroxine is beneficial for subsequent intellectual outcome in children with congenital hypothyroidism but may be associated with internalizing behavior problems. (J PEDIATR 1995;126:380-6)

Section snippets

Sample

Subjects were 65 female and 29 male children born between 1976 and 1985 with CH detected by one of two screening programs.14, 15 These children represented more than 90% of a larger cohort that was participating in a long-term prospective study to evaluate outcome after screening, most since the age of 1 year.16 Nonparticipants included 5 children who moved, 2 with transient hypothyroidism, and 4 dropouts; one child with an IQ less than 60, unrelated to his thyroid hormone deficiency, was

RESULTS

The results were initially analyzed to compare the effects of low and very low starting doses of L-thyroxine given to the first patients in the study. A comparison of children started with an L-thyroxine dose of 5.0 μg/kg or less and with 5.1 to 7.7 μg/kg indicated no differences. Similarly, comparisons between the HDG and all children receiving the lower dose versus only those receiving a moderate dose (i.e., "knocking out" the lowest doses) also indicated no differential effects. Therefore

DISCUSSION

These findings indicate that, in the treatment of CH, better intellectual outcome is associated with a higher starting dose of L-thyroxine. Particularly affected are verbal and memory competencies, as well as reading comprehension; perceptual skills are generally less affected. The relationships are not linear, but a threshold effect is indicated: children at the lowest dose levels (<5.0 μg/kg) did not differ from those with moderately low levels, whereas those at the highest dose levels (>10.0

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  • Cited by (0)

    From the Department of Pediatrics (Endocrinology Division) and the Department of Psychology, University of Toronto and Hospital for Sick Children, Toronto, Canada

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    Supported in part by research grants to Drs. Rovet and Ehrlich from the Ontario Mental Health Foundation and the Ontario Ministry of Health.

    Reprint requests: Joanne F. Rovet, PhD, Department of Psychology, Hospital for Sick Children, 555 University Ave., Toronto, Ontario M5G 1X8, Canada.

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    0022-3476/95/$3.00 + 0 9/20/61659

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