Association of Emerging β-Amyloid and Tau Pathology With Early Cognitive Changes in Clinically Normal Older Adults

Background and Objectives Alzheimer disease (AD) clinical trials are moving earlier in the disease process according to emerging signs of beta-amyloid (A beta) and tau pathology. If early treatment is the right time for intervention, it is critical to find the right test to optimize cognitive outcome measures for clinical trials. We sought to identify cognitive measures associated with the earliest detectable signs of emerging A beta and tau pathology. Methods One hundred twelve clinically normal adults with longitudinal Pittsburgh compound B (PiB)-PET, F-18-flortaucipir (FTP)-PET, and cognitive data for >= 7 years were included from the Harvard Aging Brain Study (HABS). Analyses assessed those initially classified as PiB- (less than Centiloid [CL] 20) and then expanded to include PiB+ individuals up to CL40, the approximate threshold beyond which neocortical tau proliferation begins. Separate linear mixed-effects models assessed the effects of emerging global A beta (PiB slope) and tau (baseline FTP level and FTP slope) in the entorhinal and inferior temporal (IT) cortices on multiple cognitive tasks and the Preclinical Alzheimer's Cognitive Composite (PACC) over time. Results Steeper PiB slopes were associated with declining processing speed (Digit Symbol Substitution Test [DSST], Trail Making Test Part A) in those CL40). Discussion Early, A beta-mediated cognitive slowing was detected for processing speed measures, while early memory retrieval declines were associated with emerging A beta and tau pathology. Composites of these measures may help determine whether anti-A beta or anti-tau therapies administered at the first signs of pathology might preserve cognitive function. Classification of Evidence This study provides Class I evidence that in clinically normal older adults, emerging PET-detected AD pathology is associated with declining processing speeds and memory retrieval.