Children with attention deficit hyperactivity disorder (ADHD) display anatomical brain abnormalities beyond chemical imbalance, according to a presentation at the annual meeting of the Radiological Society of North America (RSNA). Stimulant medications prescribed to balance brain chemistry appear to normalize some of these brain irregularities, a second study reported.

"We found abnormality of the fiber pathways in the frontal cortex, basal ganglia, brain stem and cerebellum," said lead author of both studies, Manzar Ashtari, PhD. "These areas are involved in the processes that regulate attention, impulsive behavior, motor activity, and inhibition---the key symptoms in ADHD children. They are also known to be part of a bigger circuit in the brain that establishes communication between the frontal lobe and cerebellum."

According to the National Institute of Mental Health, the disorder affects 3 to 5 percent of children in the United States. Affected children have difficulty controlling their behavior or focusing their attention.

Using diffusion tensor imaging (DTI) to compare 18 affected children with 15 control children to evaluate the brain's white-matter fiber development, the American team found differences in the brain fiber pathways that transmit and receive information among brain areas.

"Typically ADHD is described as a chemical imbalance, but our research has shown that there may also be subtle anatomical differences in areas of the brain that are important in this disorder," said co-principal investigator Sanjiv Kumra, MD.

In the second study, researchers found that children who received stimulant treatment for ADHD had fewer white matter abnormalities than children who did not receive medication.

Patients consisted of two groups, each comprised of 10 children with the disorder. The first group had not taken medication or had been minimally exposed to medications. The second group was exposed to stimulants for an average of 2.5 years. Each of these groups was compared with 10 age- and gender-matched controls. The medicated children exhibited a normalization effect in fiber pathways of several brain areas.

"The findings from this small, cross-sectional study indicate that the therapeutic effect of stimulants may involve a brain normalization process," Kumra said.

Most people diagnosed with the disorder in childhood continue to have problems in adolescence and adulthood. "Despite progress in the assessment, diagnosis and treatment of ADHD, this disorder and its treatment have remained controversial," said coauthor Andrew Adesman, MD. "This study is yet further proof that children with ADHD differ at a neurobiological level compared to children without the disorder."

Ashtari said further studies with larger patient groups must be conducted before offering parents advice for diagnosis or treatment.