Is the relationship between cortical and white matter pathologic changes in multiple sclerosis spatially specific? A multimodal 7-T and 3-T MR imaging study with surface and tract-based analysis

Purpose: To investigate in vivo the spatial specificity of the interdependence between intracortical and white matter (WM) pathologic changes as function of cortical depth and distance from the cortex in multiple sclerosis (MS), and their independent contribution to physical and cognitive disability. Materials and Methods: This study was institutional review board–approved and participants gave written informed consent. In 34 MS patients and 17 age-matched control participants, 7-T quantitative T2* maps, 3-T T1-weighted anatomic images for cortical surface reconstruction, and 3-T diffusion tensor images (DTI) were obtained. Cortical quantitative T2* maps were sampled at 25%, 50%, 75% depth from pial surface. Tracts of interest were reconstructed by using probabilistic tractography. The relationship between DTI metrics voxelwise of the tracts and cortical integrity in the projection cortex was tested by using multilinear regression models. Results: In MS, DTI abnormal findings along tracts correlated with quantitative T2* changes (suggestive of iron and myelin loss) at each depth of the cortical projection area (P , .01, corrected). This association, however, was not spatially specific because abnormal findings in WM tracts also related to cortical pathologic changes outside of the projection cortex of the tract (P , .001). Expanded Disability Status Scale pyramidal score was predicted by axial diffusivity along the corticospinal tract (b = 4.6 3 103; P , .001), Symbol Digit Modalities Test score by radial diffusivity along the cingulum (b = 24.3 3 104; P , .01), and T2* in the cingulum cortical projection at 25% depth (b = 21.7; P , .05). Conclusion: Intracortical and WM injury are concomitant pathologic processes in MS, which are not uniquely distributed according to a tract-cortex–specific pattern; their association may reflect a common stage-dependent mechanism.