Stimulant medications have been previously reported to normalize the brain white matter volume in treated ADHD children as compared to drug naïve patients. We applied a more sensitive technique of diffusion tensor imaging (DTI) to examine the underlying white matter (WM) fiber bundles in a cross sectional study of medicated and drug naïve ADHD patients.
METHOD AND MATERIALS
Patients consisted of two groups of 10 drug naïve (M=2.3D, med) and 10 medicated (M=2.6Y, med). Each group of patients were closely matched in gender and age with their own respective normal controls. 25 direction DTI with matching FSE and 3D SPGR sequences were obtained. DTI images were corrected for spatial distortion. FA images of all subjects were transferred into Talairach space. The intra subject registration was accomplished using a linear rigid-body transformation. Voxelwise statistical analysis was carried out using a two-tailed t test (p<0.01) followed by an extent threshold criteria of 100 contiguous voxels. FA analysis was corrected for white matter content in each voxel.
Analysis of drug naïve ADHD patients showed many more areas with lower FA including the right midbrain, orbitofrontal, fronto-striatal, cerebellum, bilateral temporal, cingulate, and bilateral optic radiation fiber bundles. Fewer areas of FA abnormalities were present in medicated group. These areas were limited to bilateral pons and bilateral prefrontal fiber bundles.
Castellanos et al were the first to report brain WM volume normalization in medicated ADHD patients. The WM microstructural abnormalities that can be detected by DTI may form the basis for macroscopic findings in volume reduction of WM. Our results show that children who have been treated with stimulants have fewer areas of FA abnormalities than drug naïve ADHD patients. These results are preliminary as they are concluded from a cross sectional small sample. Studies such as this can have potential confounds such as age, gender, race, IQ, etc. Currently we are in the process of obtaining follow-up DTI scans of our drug naïve patients to enhance these results. These findings are promising in that they are consistent with earlier results of Castellanos et al.