Neocortical metabolic abnormalities precede nonmemory cognitive impairments in early dementia of the Alzheimer type: longitudinal confirmation.

Patterns or regional cerebral metabolism and neuropsychological function were studied longitudinally in 10 mildly demented patients with dementia of the Alzheimer type (DAT) and compared to those of moderately demented patients and controls. As reported previously (Haxby et al., 1986), the mildly demented patients initially had significant neocortical metabolic abnormalities, namely parietal reductions and right-left asymmetries, but did not differ from controls on any test of neocortically-mediated visuospatial and language functions. Right-left metabolic asymmetries correlated with neuropsychological discrepancies between visuospatial and language function in moderately demented but not mildly demented patients. We now report that longitudinal studies of these mildly demented patients showed significant decline of nonmemory cognitive function. Moreover, correlations of metabolic asymmetries with neuropsychological discrepancies between visuospatial and language functions became significant. These longitudinal results confirm our previous conclusion that neocortical metabolic abnormalities precede neocortically-mediated neuropsychological impairments in early DAT.