Measuring how well children with attention deficit hyperactivity disorder (ADHD) can control their hand movements could help to gauge the severity of their disorder, a new study suggests.

Children with ADHD were twice as likely to have a hard time keeping their right hand completely still while tapping the fingers of their left hand, compared with kids without the disorder, said study researcher Dr. Donald L. Gilbert, of Cincinnati Children's Hospital Medical Center.

Moving one side of the body to match the actions of the other side of the body is called a mirror movement, Gilbert said. As children mature past toddlerhood and improve their motor control, mirror movements generally decrease, but researchers have long known that mirror movements go away more slowly in kids with ADHD, he said.

Measuring the extent to which kids with ADHD have outgrown these automatic mirror movements provides a "reliable, quantitative, brain-based tool, so that scientists can know what's going on in the brain to identify new and better treatments," Gilbert told MyHealthNewsDaily.

The study will be published tomorrow (Feb. 15) in the journal Neurology.

Mirrors and brain activity

In the first mirroring study, researchers examined the mirror movements of 25 right-handed boys and girls, ages 8 to 15, with ADHD , and 25 right-handed boys and girls without the disorder. Researchers attached a device that measures movement to the children's left hands.

When the children were asked to tap the fingers of their left hand while keeping their right hand still, the kids with ADHD were more than twice as likely to also move their right hand as the children without ADHD, the study said.

The effect was most pronounced in boys with ADHD they were almost four times more likely to move their right hand along with their left than boys without ADHD, the study said.

In a second, related study, the scientists measured the brain activity of 49 children with ADHD and 49 children without the disorder to see if there were any differences in the motor control areas of their brains.

They found that the activity of the brain's braking mechanism that would normally put a stop to mirror movements was reduced by 40 percent in the kids with ADHD, compared with the kids without the disorder, the study said. And the reduction in activity correlated to the severity of ADHD symptoms reported by the kids' parents.

The researchers also measured the kids' coordination, rhythm, manual dexterity and balance using motor development tests. They found that kids with ADHD scored 60 percent worse than the kids without ADHD.

Applying the findings

By objectively measuring the behavior of kids with ADHD, it's possible to quantify the severity of the disorder, said study researcher Dr. Stewart Mostofsky, director of the Laboratory for Neurocognitive and Imaging Research at the Kennedy Krieger Institute in Baltimore, Md.

The tests "may prove helpful in improving diagnosis and guiding effective therapies," Mostofsky told MyHealthNewsDaily.

But the tests likely won't be used for diagnosing ADHD, simply because these deficits in the ability to control hand mirroring can't be observed until the child is older, Gilbert said.

Current methods of assessing ADHD severity are "still somewhat crude," said Dr. Jonathan Mink, a neurology professor at the University of Rochester Medical Center in New York, who was not involved with the study. Rating scales assess the number of symptoms and how often they are present, but they don't look at the underlying neurobiology, he said.

The hand-mirroring test "provides important clues as to why many kids with ADHD have clumsy movements or bad handwriting," Mink told MyHealthNewsDaily.

The mirroring test could be useful for determining which kids are at highest risk of having motor difficulties and may lead to earlier intervention for these difficulties, he said.

Pass it on: Measuring hand movements and motor region brain activity in kids with ADHD can help to quantify the severity of their disorder.

Follow MyHealthNewsDaily staff writer Amanda Chan on Twitter @AmandaLChan.