Brain amyloid, cortical thickness, and changes in activities of daily living

To examine the association of baseline elevated brain amyloid and neurodegeneration with changes in activities of daily living in participants without dementia (ND; i.e., cognitively unimpaired and participants with mild cognitive impairment) at baseline in the population-based Mayo Clinic Study of Aging.

We included 1747 ND participants with ¹¹ C-PiB PET and MR imaging in the study, with data on activities of daily living (as assessed by the Functional Activities Questionnaire (FAQ) and the Clinical Dementia Rating scale Sum of Boxes for functional domains (CDR-SOB (functional)), with a median (range) of 4.3 (0.0-12.7) years of follow-up. Abnormal (elevated; A+) ¹¹ C-PiB-PET retention ratio was defined as standardized uptake value ratio ≥ 1.48, and abnormal (reduced) AD signature cortical thickness as ≤ 2.68 mm (neurodegeneration; N+). Associations were examined with mixed effects models, adjusting for age, sex, education, apolipoprotein E ε4 allele carrier status, and global cognitive z-score.

Mean age (SD) was 71.4 years (10.1), 46.7% were females, 195 (11.2%) had A+N-, 442 (25.3%) had A-N+, and 339 (19.4%) had A+N+ biomarkers. The A+N+ group had the largest annualized change in the FAQ score from baseline (difference in annual change A+N+ vs. A-N-; ß (SE): 0.80 (0.07)); associations were substantially attenuated when a time-varying global cognitive composite was included in the model (A+N+ vs. A-N-; ß (SE): 0.31 (0.05)). CDR-SOB (functional) findings partly agreed with FAQ score findings.

The longitudinal increase in functional limitations is greater for individuals with abnormal neuroimaging biomarkers, especially for those with both elevated brain amyloid and neurodegeneration.