Diffusion tensor imaging reveals cause of ADHD

The disruption of dopamine transportation in brain white matter may be the underlying reason that children suffer from attention-deficit/hyperactivity disorder, or ADHD. In addition, MR diffusion tensor imaging suggests that drug therapy repairs the damaged fiber bundles indicated in ADHD pathology.

Previous structural and functional MR studies had found whole-brain volumetric and functional differences in the right frontal lobe and cerebellum of patients with ADHD. Using diffusion tensor imaging (DTI) for the first time to study this population, researchers at North Shore-Long Island Jewish Health System recorded microscopic damage to the brain's white matter. A surprising involvement of the brain stem in ADHD children has led researchers to hypothesize that a brain circuit involving the frontal lobe and the cerebellum may be malfunctioning in these children.

Mansar Ashtari, Ph.D., and colleagues used 25-direction DTI to image 18 patients diagnosed with ADHD and 15 controls. Areas of the brain that showed the most significant differences in fractional anisotropy (the measurement of water motion between axons in white matter) between ADHD patients and controls were the right pre-motor, anterior limb of the right internal capsule, right cerebral peduncles, left middle cerebellar peduncle, left cerebellum, and left parieto-occipital area. An unexpected finding was brain stem involvement in the ADHD patients. When Ashtari connected the affected areas, she was surprised to find they formed a known circuit called the cortocopontocerebellar.

Because of the involvement of the brain stem, which produces dopamine, Ashtari hypothesized that a disruption in the cortocopontocerebellar circuit would cause deficits of dopamine to multiple brain regions areas known to control attention and motor activities. More research is needed to confirm tthis theory, she said at the RSNA meeting.

In a second study, Ashtari and colleagues found that ADHD children who have been treated with stimulants have fewer areas of fractional anisotropy abnormalities than drug-naive ADHD patients.