Mapping of Subcortical White Matter Abnormality in Alzheimer's Disease Using Diffusion-Weighted Magnetic Resonance Imaging

Rationale and Objectives: White matter (WM) abnormality in Alzheimer's disease (AD) has been less well characterized than cortical damage. We studied the spatial distribution of the subcortical WM abnormality using diffusion-weighted magnetic resonance imaging (DWI). Materials and Methods: Twenty-one AD patients and seven healthy, elderly subjects were included. DWIs were obtained using a cerebrospinal fluid (CSF)-nulled pulse sequence to reduce the partial volume contamination of CSF signal. Diffusivity in the subcortical WM voxels was mapped onto the cortical surface using original software so that the spatial distribution of subcortical WM damage, which was visualized as an area of increased diffusivity, could be viewed in a three-dimensional map. The damages in the lateral surface of the bilateral cerebral hemispheres were visually evaluated, and severities of the damages in five brain regions were compared with each other. In addition, the severity of the damage in each region was correlated with patient's mini-mental state examination (MMSE) score. Results: In both hemispheres, clear sparing of the pericentral regions and predominant involvement of the parietal and temporal regions were revealed with statistical significance (P < .05, respectively). Marginal correlation (P < .05 uncorrected for multiple comparisons) was observed between the damage severity in the bilateral frontal and right temporal regions and patient's MMSE score. Conclusion: We demonstrated a subcortical WM abnormality over the parietal and temporal regions with clear sparing of the pericentral region using our mapping method, which supported the hypothesis that the subcortical WM abnormality in AD originates in Wallerian degeneration.