Longitudinal study of the early neuropsychological and cerebral metabolic changes in dementia of the Alzheimer type.

To examine the progression of neuropsychologic and metabolic changes in the early stages of dementia of the Alzheimer type (DAT), we studied 11 midly demented patients longitudinally. Three aspects of neuropsychological function were measured: memory, attention to complex sets and abstract reasoning, and lateralized functions, i.e., language and visuoconstruction. Regional cerebral metabolic rates for glucose were measured in frontal, parietal, and temporal association cortices. Our results show that, in general, memory deficits are the first neuropsychological impairments to occur in DAT, followed by problems with attention to complex cognitive sets and abstract reasoning, which are followed in turn by deficits in language and visuospatial abilities. In addition, neocortical metabolic abnormalities usually precede impairment of neocortically mediated attention and abstract reasoning by 8 to 16 months, and precede impairment of neocortically mediated language and visuospatial function by 12 to 37 months. These findings suggest that the first nonmnestic neuropsychological consequence of neocortical physiological dysfunction in DAT is a loss of attentional capacity. Since neocortical metabolic changes generally precede the appearance of neocortically mediated neuropsychological dysfunction, physiologic dysfunction may exist for some time before cognition is affected.