For ADHD Motor Control May Be A Concrete Identifier

June 19, 2012
For children with Attention Deficit Hyperactivity Disorder (ADHD), diagnosis can be a tricky -- and not always tangible -- thing.

For children with Attention Deficit Hyperactivity Disorder (ADHD), diagnosis can be a tricky -- and not always tangible -- thing.

Like so many psychological and developmental disorders, there is no one test to detect ADHD, at least not with any certainty. Not only must a child demonstrate a certain number of symptoms, but the responsibility for picking up on those symptoms -- and for putting two and two together to make a diagnosis -- often falls to the child's parents or teachers.

Meanwhile, ADHD symptoms can be open to interpretation. After all, many people experience bouts of inattentiveness, hyperactivity, or impulsiveness, and don't necessarily have ADHD. So how does a physician, let alone a parent, tell the difference between ADHD symptoms and the typical hyperactivity that most 7-year-olds experience, or the tendency toward procrastination so common to the average adolescent? Further complicating the issue, physicians often struggle to craft a prognosis for their patients, making it difficult to develop long-term treatment plans.

That gap is what Kennedy Krieger neurologist Stewart Mostofsky and his colleagues may be on the path to filling. So far, Mostofsky says, at least one measure in particular shows potential for gauging brain function and symptom severity in children with the disorder: poor motor control.

In one Institute study -- performed in collaboration with Cincinnati Children's Hospital Medical Center and published in 2011 in Neurology Today -- children with and without ADHD performed a finger-tapping task while researchers observed and took note of any unintentional "overflow" movements occurring on the opposite hand. Such movements -- also called mirror movements or excessive motor overflow -- are unintentional and often seem to bilaterally mimic movements made by the opposing hand, foot, or limb. Of the kids in the study, those with ADHD showed more than twice the amount of overflow demonstrated by typically developing children.

Among children with ADHD, poor motor control -- including fidgeting, foot tapping, and excessive hand movements -- is a hallmark. But this study marked the first time scientists have been able to quantify the degree to which ADHD is associated with poor motor control.

Standing between ADHD and a more widespread understanding of it are the kinds of concrete markers that make other developmental disorders more perceptible and substantial. "Despite its prevalence, there is a lack of understanding about the neurobiological basis of ADHD," says Mostofsky, director of the Laboratory for Neurocognitive and Imaging Research at the Kennedy Krieger Institute. "A critical obstacle in ADHD is the lack of quantitative measures of brain function that would provide a basis for more accurate diagnosis and effective treatment."

Though motor overflow is particularly prevalent in cases of ADHD, says Mostofsky, it's actually common in all children up to a certain age. Once you know what to look for, it can be fairly easy to spot. If a child is walking on his heels, for instance, he might mimic his steps and posture with his hands. Or if he's tapping one finger on his desk, a quick glance at the same finger on the opposite hand might show he's mimicking those same movements.

While most outgrow these kinds of movement patterns, in individuals with ADHD such movements often persist. "Evidence shows that there is greater overflow in individuals who have excessive inattentive, hyperactive, and impulsive behavior," Mostofsky says. "In 2003, we were the first to actually examine this in a cohort of children diagnosed with ADHD and find they showed excessive overflow movements."

Mostofsky and his colleagues have conducted several related studies since 2003, each demonstrating the presence of motor overflow in kids with ADHD. Additional study showed that this motor sign was particularly prevalent in boys with ADHD, aged 8 to 12 years old. "We think this is important because it demonstrates that these kids have problems with inhibiting voluntary actions," Mostofsky says. This matters, he continues, because for years, fidgeting and an inability to sit still in children with ADHD has been treated as a behavioral, rather than a physiological, problem.

In other words, it may not be a lack of discipline, but a physical inability to control unnecessary and unwanted movements. "The motor overflow isn't at all under children's behavioral control," Mostofsky explains. Further, he continues, "We found that this decreased capacity to inhibit these movements was highly predictive of ratings of their ADHD symptom severity."

Kennedy Krieger Institute Announces Retirement of President and CEO

Dr. Gary W. GoldsteinThe Institute’s board of directors is conducting a national search and is expected to name a new CEO in the coming months.
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