Parenchymal CT correlates of senile dementia (Alzheimer disease): loss of gray-white matter discriminability.

Neuropathologic studies have defined gross anatomic (structural) as well as histologic (parenchymal) changes of senile dementia (Alzheimer disease). This investigation suggests that loss of gray-white matter discriminability by computed tomography (CT) is related to cognitive impairment in this disease. Discriminability is defined as the relative ease of visual differentiation between gray and white tissues. Twenty-six elderly patients with dementia were subjected to extensive psychometric evaluation, a medical and neurologic examination, and CT scanning. Gray and white matter changes were assessed by subjectively evaluating three brain levels, the basal ganglia, the centrum semiovale, and the high convexity, on a five point scale. Quantitated gray and white matter scores were also obtained by sampling CT attenuation values. In addition, CT structural changes were evaluated by previously reported methods. there were significant correlations (P less than 0.05) between the subjectively assessed loss of gray-white matter discriminability at all brain levels and the measures of cognitive decline. At the high convexity level 91% of cognitive measures correlated with loss of gray-white discriminability. In the same patient group no gray-white discriminability correlation with age was demonstrated suggesting that gray-white discriminability does not simply change with age.