White matter low attenuation on computed tomography in Alzheimer's disease and vascular dementia--diagnostic and pathogenetic aspects.

Demented patients with early-onset Alzheimer's disease (AD) (n = 17), late-onset Alzheimer's disease (n = 30) and vascular dementia (VD) (n = 20) were studied with computed tomography of the brain. Semiquantitative evaluation of white matter low attenuation (WMLA) and central and cortical atrophy was performed without knowledge of the clinical diagnosis. In early onset AD there was almost complete absence of WMLA and central atrophy compared with the other groups, which showed moderate to severe changes. This suggests that early-onset AD should be separated from the late-onset form. The increased systolic blood pressure found in the WMLA group supports the opinion that WMLA has a vascular origin. The high percentage of WMLA in VD and late-onset AD indicates that subcortical factors have to be considered in the pathogenesis of these disorders.