The purpose of this study was to delineate the specific patterns of cerebral glucose metabolism with regard to the time of onset of Alzheimer's disease (AD).
Methods: Two groups of 20 AD patients with different ages of onset were examined. The early onset (EO) and late onset (LO) groups had mean ages of onset of 53.9 and 72.7 years. Groups of age-matched normal subjects were used as controls. A regional relative cerebral glucose metabolic image of each subject was obtained by 2-[18F] fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET). NEUROSTAT program was used for spatial normalization and voxel-based statistical parametric mapping (SPM) 99 was used for statistical analyses.
Results: Both AD groups had significant hypometabolic regions in the bilateral parieto-temporal regions compared with the age-matched groups. The EO group had more severe hypometabolism in the bilateral parietal and posterior cingulate cortices and precuneus region than the LO group. However, LO group showed no significant hypometabolic regions compared to the EO group.
Conclusion: The effects of time of AD onset were delineated as a double dissociation, that is, EO AD patients have a more severe reduction of glucose metabolism. Our finding suggests the existence of biological subtypes of AD.