Researcher Perry F. Renshaw, MD, and colleagues say that children with the "hyperactivity" type of attention deficit disorder also have abnormally low activity in a part of the brain that governs movement, planning, coordination, and learning.
The low activity shows up as less blood flow to that area and can be detected using the new "functional magnetic resonance imaging" (fMRI) method that the researchers developed. Their work is described in this week's issue of Nature Medicine.
Ritalin increases activity in this region in some children with ADHD, and with this change comes improvements in their ability to sit still, pay attention, and complete tasks.
"So far, we do not have objective, reliable guidelines for diagnosing ADHD," Renshaw tells WebMD. "Lots of parents and children are done a disservice by current practices because there are not good standards for establishing a diagnosis.
"There also aren't good ways to determine if a specific child is likely to benefit from Ritalin. If we can do a better job in deciding which patients with ADHD should be treated with Ritalin or other stimulants, that could help a lot of people."
Renshaw, the lead researcher on the study, tells WebMD, "We found that in children with ADHD and hyperactivity, there [appears to be] less blood flow in the hyperactive ADHD children when they are not medicated. Ritalin substantially reduced the behavioral problems of ADHD children who were hyperactive but had little effect on those who had attention deficit disorder without hyperactivity."
There was an extremely strong correlation between the measurements of brain blood flow and the children's improvements in activity and in attention, Renshaw said
Renshaw and associates tested the fMRI method on six healthy boys and in 11 boys with ADHD. The boys with ADHD were found to have less blood flow in the important brain region than those without the disorder. Daily doses of Ritalin improved brain activity in the hyperactive ADHD boys but had little effect on the ADHD subjects who were not hyperactive.
Renshaw's technique can be done with equipment found in most medical centers that do MRI, but special computer software must be used to analyze the images.