Two imaging modalities are now offering new insight into the cause of attention deficit/hyperactivity disorder, according to researchers. While one group of investigators took a look at the connection between brain lesions and ADHD, the other studied the neurochemistry that may contribute to the disorder.
ADHD affects an estimated 3% to 9% of all school-age children and can continue on into adulthood, although diagnosing the disorder is a matter of controversy. Behavorial specialists generally rely on observation because there is no objective method in place to pinpoint the disorder. Patients with ADHD have short attentions spans, have difficulty concentrating and can be aggressive.
Researchers at Johns Hopkins Medical Institutions in Baltimore studied whether brain lesions, suffered as a result of closed-head injuries, could be predictive of secondary ADHD. The group obtained data from 76 children, ages 4 to 19, who had either severe or moderate closed-head injuries as determined by the Glasgow Coma Scale. All of the subjects had been comatose for at least a few days, if not longer, according to Dr. Edward Herskovits, one of the study's authors and a postdoctoral fellow in the division of neuroradiology at Johns Hopkins.
MR examination of the brain included the following: T-1 sagittal localizing sequence with 5-mm section thickness; spin-echo spin-density-weighted and T2-weighted oblique transverse images with 5-mm section thickness; and T-1-weighted spoiled gradient-recalled echo oblique transverse images with a 1.5-mm section thickness.
The information was then fed into BRAID, a brain-image, object-relational database. BRAID operates in three functional modes: visualization, analysis and exploration. Of the 76 subjects, 20% had developed secondary ADHD. That group also showed higher lesion fraction in the right putaman than the 80% of the subjects who did not develop ADHD (Radiology, November 1999, Vol. 213:2, pp.389-394).
While Herskovits isn't advocating that all children who suffer head injuries undergo MR imaging, he said it can be a useful tool to track patient progress.
"I don't know if it should be mandatory. It might be useful in terms of prognosis," Herskovits said. "If a child has a head injury and has the MR done three months later and you see lesions in the basal ganglia, it would be harder to write off ADHD. It could be a useful adjunct to help parents and children prepare for the possibility."
Herskovits plans to further study this area by continuing to follow up on the same group of children. He also is seeking funding for a separate study on adults who suffer closed-head injuries.
Another study done by researchers in Boston tracked the role of dopamine transports in adults with ADHD. Using SPECT, they found that the six adult subjects had dopamine transporter levels that were 70% higher than normal.
All patients, including six adults with ADHD and 30 healthy controls, were injected with five to seven mCi of iodine-123 altropane. SPECT images were acquired with two- or three-head gamma cameras.
The overexpression of the dopamine transporter gene may be causing the ADHD, concluded researchers at Massachusetts General Hospital (The Lancet, Dec. 18, 1999, Vol. 354, pp. 2132-2133).
SPECT could offer a reasonable screening test to determine if a patient actually has ADHD before administering psychomotor stimulants, such as Ritalin, said Alan Fischman, chief of nuclear medicine at MGH (Wall Street Journal, Dec. 17, 1999).
Herskovits said his team will stay with MRI because of its ability to show the localization of brain lesions. Future follow-up studies also will take a look at other factors that may influence ADHD, such as socioeconomic background.
By Shalmali Pal
AuntMinnie.com staff writer
February 8, 2000
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