[Diffusional anisotropy in the cerebral white matter in Alzheimer-type dementia]

To investigate changes in water diffusion in the cerebral white matter in Alzheimer-type dementia (AD), diffusion MRI studies were performed on 11 patients with AD without hyperintensity lesions on T2-weighted images, and 10 age-matched controls. In the anterior and posterior white matter around the lateral ventricule, and the splenium of the corpus callosum, the apparent diffusion coefficients (ADCs), in which the diffusion gradient was applied perpendicular to the predominant fiber direction, were significantly higher in patients with AD than in the controls. However, those in which the diffusion gradient was applied parallel to the predominant fiber direction, there were no significant difference in ADCs between patients and controls. Therefore, diffusional anisotropy was lost in the white matter. These results suggest that demyelination occurs in patients with AD even in apparently normal white matter (without signal abnormalitis). Degeneration related to grey matter encephalopathy may be a possible explanation of the demyelinating process in the white matter.