The cause of attention deficit hyperactivity disorder, which affects roughly 5.4 million kids in the United States alone, remains unknown. But new research into "mirror movements" sheds light on the mysterious neurobehavioral disorder and might even aid in its diagnosis.
Researchers at the Kennedy Krieger Institute in Baltimore studied 50 children between the ages of 8 to 13 who had been diagnosed with ADHD, and 25 who hadn't, as they tapped the fingers of one hand while resting the other in their laps. The ADHD kids showed increased mirror movements, meaning the voluntary finger taps in one hand were involuntarily reflected in the other.
Boys with ADHD had more than twice as many mirror movements than children without ADHD when they tapped with their nondominant hands. The difference was not seen in girls.
The study was published Feb. 14 in Neurology.
In an accompanying editorial, Dr. Jonathan Mink, professor of neurology and pediatrics at the University of Rochester Medical Center, wrote that the study provides "important evidence for impaired inhibitory function in ADHD."
Although ADHD has long been linked with motor symptoms, such as poor handwriting, the study suggests that measuring hand movements could become a useful test in diagnosing ADHD.
"This would be quite valuable," said Michael Manos, who directs the pediatric behavioral health department at the Cleveland Clinic Children's Hospital. "Even more important is the possibility that the methods, once developed, would assist us to monitor response to the medical treatment of ADHD."
But Manos urges parents to not use motor movements to diagnose ADHD in their children.
"Parents who want to test their own children for ADHD using this method are only asking for worry and frustration added o their existing worry and frustration. The only advice is: Don't do it. More work must be done."
Dr. David Rosenberg, chairman of child psychiatry at Wayne State University School of Medicine, said the finger tapping test emphasized that ADHD is a brain disease that can be detected and treated. But he, too, cautions that the diagnosing of ADHD should be left to trained medical professionals.
"Such tests may be of interest and ultimately help identify more objective measures of illness, but at present this requires replication and cannot be considered diagnostic," he said.