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SATURDAY, JULY 18, 2015ALZHEIMER'S IMAGING CONSORTIUM (IC)IC-02ATYPICAL ALZHEIMER'S AND OTHER DEMENTIAS| Volume 11, ISSUE 7, SUPPLEMENT , P5, July 01, 2015

Characterizing patterns of atrophy between cognitively unimpaired healthy elderly controls with either Alzheimer's disease or suspected non-Alzheimer's disease pathophysiology

      Background

      Suspected non–Alzheimer disease pathophysiology (SNAP) has been recently defined as the presence of AD-like neurodegeneration in the absence of Aβ deposition. In this study, we try to identify the pattern of cortical grey matter (GM) atrophy in cognitively unimpaired healthy elderly controls (HC) when hippocampal volume is used to define neurodegeneration, and ascertain if this pattern is different in those with or without AD pathology.

      Methods

      320 cognitively unimpaired subjects were assessed using PET (PiB, flutemetamol or florbetapir) and MRI as part of the AIBL study. Aβ status (A) was determined using CapAIBL©, while neurodegeneration (N) was established using hippocampal volume (HV) measured with FreeSurfer. Following Jack et al, (2012, 2013) subjects were categorized as A-N-, A+N-, A+N+, or A-N+ (SNAP). Regional GM volumes at baseline and rates of atrophy for subjects with repeat imaging timepoints (N=135) were compared. Volumes were adjusted for age and intra-cranial volume. Statistical tests were corrected for multiple comparisons.

      Results

      At baseline, 63% (N=203) of subjects were classified as A-N-, 15% (N=48) as A+N-, 5% (N=16) as A+N+, and 17% (N=53) as SNAP. Compared to A-N-, A+N- had no GM atrophy, SNAP had atrophy in all regions but the cuneus, posterior cingulate, and post-central gyrus, while A+N+ had GM atrophy in all regions except for the cuneus and pre/post-central gyri. Compared to A+N-, SNAP had significant GM atrophy in the inferior temporal (p<0.0001). Compared to SNAP, A+N+ had more atrophy in precuneus (p<0.005). SNAP had similar rates of atrophy than A-N-, A+N- had faster atrophy rates (p<0.05) than A-N- in the temporal, precuneus and occipital, and A+N+ had faster atrophy rates (p<0.05) than A-N- in all regions but the anterior cingulate.

      Conclusions

      At baseline, the pattern of GM atrophy in SNAP was more extensive than in A+N-, while the rates of atrophy did not differ from A-N-, suggesting SNAP, as defined by HV, comprise different underlying pathologies, and are on a different trajectory than those with AD pathology.