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Thyroid hormone and attention in congenital hypothyroidism
Objectives:
To determine in school-age children with congenital hypothyroidism: (i) frequency of a high thyroxine/high thyrotropin profile; (ii) relations between different levels of thyroxine and thyrotropin and attentional function, and (iii) persistence of effects.
Design:
Retrospective analysis of an inception cohort.
Setting:
Clinical psychology laboratory in tertiary pediatric hospital.
Subjects:
Eighty-six 7 year olds identified with congenital hypothyroidism by newborn screening, who were participating in a long-term prospective study.
Main Outcome Measures:
Wechsler Intelligence Scale for Children-Revised (WISC-R) and Wide Range Achievement Test-Revised (WRAT-R) were administered. WISC-R Full Scale, Verbal and Performance IQs were obtained as well as scores on individual subtests, and three ability composites. Freedom from Distractibility (FFD) served as the indicator of attention.
Results:
9.3% of 7 year olds had elevations of both T4 and TSH. These children scored significantly higher on word knowledge and spelling but had significantly lower Digit Span and FFD scores than those in groups with other hormone combinations. Level of thyroxine was the primary predictor of attention, accounting for 10.5% of the variance. Among 9 year olds, 6.1% had T4 and TSH elevations, and although they also scored lowest on FFD, these were not the same children with T4 and TSH elevations at age 7.
Conclusions:
These results signify that a high T4/high TSH profile contributes to poorer attention. Because the individual children who showed the effect were not the same at the two ages, this suggests that thyroid hormone appears to play a role in regulating attention but does not indicate resistance.