Kids with attention deficit hyperactivity disorder lag three years behind their peers when it comes to brain development, a new study suggests.
The study is the first to quantify the differences in brain development between children with ADHD and their non-ADHD counterparts.
"In children with ADHD, the brain matures in a normal pattern but is delayed by three years in some regions, when compared to children without the disorder," said the study's lead investigator, Dr. Philip Shaw, a child psychiatrist at the National Institute of Mental Health.
According to the National Resource Center on ADHD, the condition is the most common neurodevelopment disorder of childhood. It is present in 5 percent to 8 percent of school age children, with symptoms persisting into adulthood in as many as 60 percent of cases.
It is most commonly diagnosed in kids but can remain undiagnosed until adolescence, and even adulthood. Children afflicted with ADHD often have difficulty concentrating in school, engage in disruptive behavior during class, and are "fidgety."
The new research, published in the journal Proceedings of the National Academy of Sciences, looked at brain development in kids with ADHD, using brain imaging techniques.
With sophisticated magnetic resonance imaging scans, Shaw and his colleagues looked at 40,000 different sites of the brain cortex in 446 children and measured brain thickness — a marker of brain maturation.
They found that in kids with ADHD, a certain part of the brain — specifically, a region in the front called the prefrontal cortex — matured approximately three years later, around the age of 10½ compared to kids without ADHD.
These areas of the brain are responsible for focusing attention and suppressing inappropriate thoughts and actions — things that are disrupted in people with ADHD.
Researchers also found that the part of the brain called the motor cortex — responsible for making different movements in the body — matured faster in kids with ADHD. The authors theorized that both of these findings together might be responsible for the restlessness and fidgety symptoms commonly seen in ADHD.
"This is a breakthrough study," said Dr. James McGough, professor of clinical psychiatry and director of the ADHD program at the University of California at Los Angeles. "It confirms what pediatricians have been saying for years. It is clear now that there is a delay in brain development."
The excitement regarding the study seems to be shared among several members of the ADHD community.
"It opens up a whole new way of thinking about ADHD," said Dr. Francisco Xavier Castellanos, professor of child and adolescent psychiatry at New York University, and the initiator of the study. "And it provides reassurance to the parents of kids with ADHD that there is a real difference in brain development in kids with ADHD.
"It is not simply bad parenting or children behaving badly."
Others say the work confirms past research, which suggests ADHD kids' brain differences.
"Numerous studies in the past have shown a decrease in volume of the brain in kids with ADHD, but we just didn't know where," said Dr. Josephine Elia, co-director of the ADHD Center at the Children's Hospital of Philadelphia.
"This study localized exactly where this volume change takes place," she said. "And it points to the prefrontal cortex, which is involved with organizing, planning, timing and sequencing of events." Elia added that these are all functions that kids with ADHD find difficult to perform.
The idea of brain imaging to detect ADHD early may seem tempting, but most doctors agree that it is not ready for use as a diagnostic tool.
"Although the delay in cortex development was marked, it could only be detected when a very large number of children with the disorder were included," Shaw noted in an NIMH press release. "It is not yet possible to detect such delay from the brain scans of just one individual. The diagnosis of ADHD remains clinical, based on taking a history from the child, the family and teachers."
"But it does lay the groundwork for using brain imaging clinically in the future," said Elia.
There is a slight word of caution, though, amid the general excitement. According to Larry Seidman, professor of psychology at Harvard Medical School, "The use of the word 'delay' could be misinterpreted to mean that children with ADHD will 'catch up.'
"As of now, we don't have evidence that they catch up in their brain development."