Beta-amyloid imaging and memory in a large cohort of elderly individuals

Abstract

132

Objectives: We previously reported a correlation between beta-amyloid burden and episodic memory in nondemented individuals but not in Alzheimer’s disease (AD). We revisited this issue using twice as many participants and a new normal range for cognitive performance that excluded apparently normal subjects with positive PiB-PET scans.

Methods: 83 healthy controls (HC), 53 mild cognitive impairment (MCI), and 51 AD participants were studied. Beta-amyloid burden was quantified using PiB-PET imaging to calculate a neocortical standardized uptake value normalized to cerebellum. Composite episodic memory and nonmemory scores were calculated using 53 PiB negative healthy controls as the reference.

Results: There were strong correlations between amyloid burden and both memory (r=-.66, p<.001) and nonmemory (r=-.45, p<.001) performance across all groups. When groups were analysed separately, the relationship between memory and amyloid burden remained significant in the MCI (r=-.59, p<.001) and HC groups (r=-.22, p=0.049). In contrast, there was no relationship between memory and amyloid burden in AD (r=.04). Nonmemory scores did not correlate with amyloid burden for any group. The relationship between memory and amyloid burden in nondemented individuals remained significant when PiB negative cases were removed (r=-.46, p<.001).

Conclusions: The strong relationship between episodic memory impairment (the earliest cognitive change in AD) and PiB uptake in nondemented individuals supports the proposal that PiB-PET can detect AD prior to development of dementia.