Hyperactivity Linked To Thyroid Hormones

HYPERACTIVITY LINKED TO THYROID HORMONESThyroid hormone may play a role in the hyperactive and impulsive symptoms of children with attention deficit-hyperactivity disorder (ADHD), University of Maryland School of Medicine researchers say. Dr. Peter Hauser, professor of psychiatry, and Dr. Bruce Weintraub, professor of medicine at the University of Maryland School of Medicine, have found a positive correlation between elevated levels of certain thyroid hormones and hyperactivity/impulsivity in a selected group of patients. They report on their research in the February issue of the international journal Psychoneuroendocrinology.

ADHD is one of the most common psychiatric problems of childhood, affecting an estimated three to five out of every 100 children. But up to now, no studies have demonstrated a physiologic basis for the differences between those suffering merely from inattention and those displaying symptoms of hyperactivity and impulsive behavior, a trait psychiatrists call impulsivity.

Having previously discovered a strong and specific association between resistance to thyroid hormone and ADHD, Hauser, Weintraub and colleagues studied 75 people diagnosed with resistance to thyroid hormone and 77 of their unaffected family members. They measured levels of three thyroid hormones - TSH, T3 and T4 - and evaluated symptoms of both inattention and hyperactivity, two constellations of symptoms that together make up ADHD.

Resistance to thyroid hormone is a thyroid disease characterized by elevated levels of serum T3 and T4, as well as inappropriately normal or high concentrations of serum TSH, evidence of a reduced response to the actions of thyroid hormones. ADHD symptoms were identified in interviews by psychologists and psychiatrists who did not know which subjects had resistance to thyroid hormone.

TSH concentrations did not correlate significantly with any of the symptoms of ADHD. High concentrations of T3 and T4, while not significant in symptoms of inattention, were significantly and positively correlated with symptoms of hyperactivity/impulsivity in thyroid hormone-resistant subjects, Hauser said.

In family members who were not resistant to thyroid hormone, neither TSH nor T4 concentrations were significantly correlated with ADHD. Elevated levels of T3, however, were signicantly correlated with hyperactivity/impulsivity symptoms but not with symptoms of inattention, he reported.

"The correlation between thyroid hormone concentrations and symptoms of hyperactivity does not prove causality," warned Hauser, chief of psychiatry at the Baltimore Veterans Affairs Medical Center, a University of Maryland School of Medicine teaching hospital. "What it does show is that thyroid hormones may provide a physiologic basis for the dichotomy between symptoms of inattention and symptoms of hyperactivity."

Hauser said the study supports the American Pyschiatric Association’s decision to combine the symptoms of hyperactivity and impulsivity in their 1994 revision of the Diagnostic Manual of Mental Disorders, the bible of psychiatric diagnosis in the United States.

"Our findings suggest that further research on the role of thyroid hormone in subjects with ADHD may be of benefit," he said.

Research data were collected while Hauser and Weintraub were on the staff of the Molecular and Cellular Endocrinology Branch of the National Institutes of Health National Institute of Diabetes and Digestive and Kidney Diseases, which funded the research.END