Roberts RO, et al. - Experts investigated the incidence and outcomes of amyloid positivity in patients without dementia in Olmsted County, Minnesota. Valid information for the design of Alzheimer's disease (AD) prevention trials and for studying public health outcomes of AD prevention and interventions was gained the by population-based prevalence of amyloid-positive status and progression rates of amyloid positivity seen.

Methods

• Participants without dementia were randomly selected from the county population in this prospective, population-based Mayo Clinic Study of Aging in Olmsted County, Minnesota.
• Enrollees were clinically and cognitively assessed at baseline and every 15 months from August 1, 2008 to September 18, 2018. They were also invited to undergo carbon¹¹-Pittburgh compound B positron emission tomography (PET) imaging.
• The primary outcome was prevalence of amyloid positivity in the Olmsted County population without dementia and risk of progression from no cognitive impairment (ie normal cognition for age) to incident amnestic mild cognitive impairment (aMCI) and from MCI or aMCI to incident AD dementia.

Results

• Among 3,894 participants, 1,671 underwent PET imaging and were involved in the study; 2,198 did not undergo imaging, and 25 were excluded for other reasons.
• The mean (SD) age of participants was 71.3 (9.8) years; 892 (53.4%) were men, and 179 (10.7%) had prevalent MCI.
• A rise was reported in the prevalence of amyloid positivity without cognitive impairment in the population without dementia from 2.7% (95% CI, 0.5% to 4.9%) in persons aged 50 to 59 years to 41.3% (95% CI, 33.4% to 49.2%) in those aged 80 to 89 years at baseline.
• Incidence of amyloid-positive MCI in the population without dementia increased from 0% in persons aged 50 to 59 years to 16.4% (95% CI, 10.3% to 22.5%) in those aged 80 to 89 years.
• In participants without cognitive impairment who were amyloid positive vs those who were amyloid negative, incident aMCI risk increased more than 2-fold (hazard ratio [HR], 2.26; 95% CI, 1.52 to 3.35; P < .001).
• Risk of AD dementia was 1.86 (95% CI, 0.89 to 3.88; P=.10) for amyloid-positive participants with MCI vs amyloid-negative participants with MCI, 1.63 (95% CI, 0.78 to 3.41; P=.20) for subjects with aMCI who were amyloid positive vs amyloid negative, and 2.56 (95% CI, 1.35 to 4.88; P=.004) for amyloid-positive participants who were either without cognitive impairment or had aMCI vs those who were amyloid negative.
• A significant decline was seen in the global cognitive and memory domain z scores for amyloid-positive individuals during follow-up.
• Mean (SD) follow-up time from baseline was 3.7 (1.9) years to incident aMCI and 3.8 (2.0) years to incident AD dementia.