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REGIONAL BETA-AMYLOID PET COMPARISON ACROSS ATYPICAL AND TYPICAL VARIANTS OF ALZHEIMER’S DISEASE

      Background

      Typical dementia of the Alzheimer’s type (DAT) presents as a primary amnestic syndrome, and three “atypical” variants are now recognized. Two of these atypical variants include posterior cortical atrophy (PCA), which presents with visual deficits and the logopenic variant of primary progressive aphasia (lvPPA), which presents with primary language disruption, both of which are commonly due to Alzheimer’s disease pathology. Here, we compare these Alzheimer’s disease variants on the pattern of beta-amyloid deposition on PiB PET, as well as cognitive measures.

      Methods

      We matched 27 PCA, 50 LPA, and 77 DAT patients on age, gender, and disease duration as best as possible. Only subjects with positive beta-amyloid deposition on PiB PET, defined using a standardized uptake value ratio (SUVR) of ≥ 1.5, were included. All voxels in the PiB-PET images were divided by median uptake in cerebellum and transformed into template space. Partial volume correction (PVC) was performed. Voxel-level comparisons were performed across groups both with and without PVC using SPM5.

      Results

      were assessed after correction for multiple comparisons using family-wise error at p<0.05.Subjects also completed memory, language, and visuospatial tests that may have been used to augment DAT and PCA diagnosis, but was not used in diagnosis of LPA. Results: Cognitively, DAT subjects had poorer memory than lvPPA and PCA subjects, lvPPA subjects had poorer language scores than DAT and PCA subjects, and PCA had poorer visuospatial scores that lvPPA and DAT subjects. The groups did not differ on global SUVR. Regional distribution of PiB-PET was similarly widespread in each of the three groups, although PCA showed greater uptake in bilateral occipital lobe compared to DAT, and greater uptake in right occipital lobe compared to lvPPA. These findings were observed both with and without PVC. No other regional PiB-PET differences were observed across groups.

      Conclusions

      These findings suggest that while beta-amyloid deposition is typically diffuse in Alzheimer’s disease variants, regional differences exist as compared to DAT, although this DAT group may represent those with an earlier onset. The occipital lobe is particularly vulnerable to beta-amyloid deposition, as well as neurodegeneration, in PCA.