Thyroid function tests and neurocognitive functioning in children referred for attention deficit/hyperactivity disorder.

BACKGROUND Thyroid abnormalities have been associated with attention deficit/hyperactivity disorder (ADHD) and with other childhood psychiatric disorders. The goal of this study was to determine the relationships between thyroid hormone concentrations, neurocognitive functioning, and psychiatric diagnosis in children. METHODS Free thyroxine index (FT4I) and thyroid stimulating hormone (TSH) were obtained, along with diagnostic and descriptive information for 338 children referred to a clinic specializing in learning and behavior problems. RESULTS Thyroid abnormalities were uncommon in children referred for ADHD. After excluding children with thyroid disease, there was a greater proportion with low concentrations of normal FT4I for ADHD-Predominantly Inattentive type (ratio=7.0), but not for ADHD-Combined Type. High concentrations of normal FT4I were associated with mood lability, preoccupations, and lower ratings of attention problems. Thyroxine concentrations within the normal range were differentially associated with ADHD-Combined Type compared to ADHD-Predominantly Inattentive, mood disorders, and pervasive developmental disorders. CONCLUSION Thyroxine concentrations were associated with mood symptoms and unusual behaviors, and were less strongly related to attentional functioning. Thyroxine concentrations were not related to hyperactivity.