Abstract
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Objectives To evaluate the change in beta-amyloid deposition in mild cognitive impairment (MCI) and cognitively normal elderly controls (CN) over 2-years of follow-up.
Methods 85 subjects (49 CN: MMSE ≥ 29; age 71±11; and 36 MCI: CDR 0.5, MMSE >24; age 71±10) had florbetapir-PET scans at baseline and two years (23±4 months) later. Scans were independently spatially normalized to a standard florbetapir PET template in Talairach space. Standard uptake value (SUVr) ratios were calculated using the mean of pre-defined anatomically relevant cortical regions (precuneus, posterior cingulate, anterior cingulate, frontal, temporal and parietal), relative to entire cerebellum. The relationship between change in SUVr and baseline PET SUVr and diagnostic group was examined.
Results SUVr values from baseline and follow-up scans were highly correlated (Pearson correlation, r=0.96), but the slope of the regression line was greater than 1, suggesting an increasing relationship between baseline and follow-up SUVr. Using an SUVr cut-off of 1.10 to define subjects considered positive for amyloid, it was found that subjects that were positive at baseline (mean SUVr= 1.37) had a significant increase in 2 year in SUVr (mean delta= +0.06; p< 0.05) whereas the subjects that were negative at baseline (mean SUVr=0.98) did not (mean delta = +0.005; p=0.40). Among the 59 subjects that were amyloid negative at baseline, 4 subjects had transitioned to amyloid positive on the follow-up scan, a transition rate of 3.5% per year. None of the subjects who were amyloid positive at baseline converted to amyloid negative on follow-up.
Conclusions These florbetapir-PET results suggest that non-demented subjects with evidence of beta-amyloid deposits have continued increases in amyloid, whereas amyloid negative subjects show no mean increase at two years. However, a small number of subjects may transition from negative to positive during this time