New study may reassure parents of kids with ADHD

The brains of children with attention deficit hyperactivity disorder develop more slowly than those of other children but eventually catch up, according to a government study published Monday.

Using advanced imaging techniques, scientists found the cortices of kids with ADHD reach peak thickness an average of three years later than children without the disorder.

The cortex is involved in decision-making and supports the ability to focus attention, remember things moment to moment and suppress inappropriate actions — functions often deficient in children with ADHD.

Dr. Philip Shaw of the National Institute of Mental Health (NIMH), lead author of the report published in Proceedings of the National Academy of Sciences, said the results could help explain why many children with ADHD appear to grow out of the disorder and become less impulsive and fidgety as they mature.

Shaw said that although brain development was slower among children with ADHD, it followed a normal pattern, which should reassure parents.

About 4.4 million school-age U.S. children have ADHD, which can lead to poor school performance and behavior problems. Half of children diagnosed with the disorder are treated with stimulants, such as Ritalin, or other medicines.

"Finding a normal pattern of cortex maturation, albeit delayed, in children with ADHD should be reassuring to families and could help to explain why many youth eventually seem to grow out of the disorder," Shaw said in a statement.

But not all children outgrow the disorder, and co-author Dr. Judith Rapoport, also of the NIMH Child Psychiatry Branch, said the researchers are working to determine the differences between those who have a good outcome and those who do not.

From 3 percent to 5 percent of school-age children are thought to have ADHD.

Dr. Louis J. Kraus, chief of child psychiatry at Rush University Medical Center in Chicago, said "what is really important about this study is it shows us there is clearly something biologically driven for children with ADHD."

Kraus, who was not part of the research team, said that with this finding no one can argue that children are making it up. "We don't know ... whether it would change any type of treatment, but it is showing that there is something biologically different."

Researchers used magnetic resonance imaging equipment to scan the brains of 223 children and adolescents with ADHD and 223 youngsters without the disorder. The scans were repeated two, three or four or more times at three-year intervals.

Scientists focused on the cortex, which becomes thicker as the brain builds new connections to process learning.

They measured cortical thickness at 40,000 points on each scan. In general, they found the parts of the cortex involved in sensory and motor processing reached peak thickness earlier than the areas responsible for decision-making and higher-order functions.

In children with ADHD, developmental lags were most pronounced in the prefrontal cortex, which supports attention and working memory. Half of the cortical points in ADHD children reached peak thickness at an average age of 10.5, contrasted with 7.5 in children without the disorder.