Age at onset and regional cerebral glucose metabolism in Alzheimer's disease.

This study assessed 46 patients with Alzheimer's disease and 21 aged controls using positron emission tomography. Repeated analyses using a general linear model examined the effect of age at onset on the pattern of the regional cerebral metabolic rate of glucose (rCMRglc). The results showed significant age effects on the rCMRglc in the fronto-temporo-parietal association cortices and retrosplenial areas. Disease duration, overall cognitive severity or normal aging could not account for the effects. The age effects were delineated as a double dissociation, that is, early-onset patients have a more severe reduction of regional glucose metabolism in the association cortices, while late-onset patients show a more prominent metabolic deficit in the paralimbic area.