The relation between attention and thyroid function was examined in 85, 7-year-old, children with congenital hypothyroidism (CH) at the Hospital for Sick Children, Toronto, Canada. Children were assigned to subgroups on the basis of concurrent T4 and TSH levels. Almost 10% of children with CH had abnormally high levels of T4 and TSH. Those with this abnormal thyroid profile did not differ from other CH children in intelligence but they did perform more poorly on a measure of cognitive attention, while rating more favorably on parent behavior scales of hyperactivity and distractibility. The level of T4 was the stongest predictor of poorer cognitive attention, while TSH levels correlated directly with hyperactivity. 
COMMENT. Higher levels of T4 and TSH, consistent with a resistance to thyroid hormone, are associated with poorer attention and less hyperactive behavior in children with congenital hypothyroidism. Children with CH should be closely monitored to maintain levels of T4 and TSH within the normal range and to avoid elevations of hormone that could impede attention. Thyroxine and thyrotropin have unique effects on specific aspects of attention and behavior.
The incidence of ADHD is 10 times higher in children with thyroid hormone resistance than in those with normal thyroid function . See Progress in Pediatric Neurology II, 1994, pp 177-8. Studies of thyroid function should be included more frequently in the clinical evaluation of children with ADHD.