Comparing PET and MRI Biomarkers Predicting Cognitive Decline in Preclinical Alzheimer Disease
May 5, 2021
Citation: Neurology. 2021 May 5 [Epub ahead of print]

OBJECTIVE To compare how structural MRI, Fluorodeoxyglucose (FDG), and Flortaucipir (FTP) PET signal predict cognitive decline in high-amyloid versus low-amyloid participants with the goal of determining which biomarker combination would result in the highest increase of statistical power for prevention trials.
METHODS In this prospective cohort study, we analyzed data from clinically-normal adults from the Harvard Aging Brain Study with MRI, FDG, FTP, and PiB-PET acquired within a year, and prospective cognitive evaluations over a mean three-year follow-up. We focused analyses on pre-defined regions-of-interest: inferior temporal, isthmus cingulate, hippocampus, and entorhinal cortex. Cognition was assessed using the Preclinical Alzheimer's Cognitive Composite (PACC5). We evaluated the association between biomarkers and cognitive decline using linear-mixed-effect models with random intercepts and slopes, adjusting for demographics. We generated power curves simulating prevention trials.
RESULTS Data from 131 participants [52 females, 73.98±8.29 years old] were analyzed in the study. In separate models, most biomarkers had a closer association with cognitive decline in the high-PiB compared to the low-PiB participants. A backward stepwise regression including all biomarkers demonstrated that only neocortical PiB, entorhinal FTP, and entorhinal FDG were independent predictors of subsequent cognitive decline. Power analyses revealed that using both high-PiB and low entorhinal FDG as inclusion criteria reduced 3-fold the number of participants needed in a hypothetical trial compared to using only high-PiB.
DISCUSSION In preclinical Alzheimer's disease, entorhinal hypometabolism is a strong and independent predictor of subsequent cognitive decline, making FDG a potentially useful biomarker to increase power in clinical trials.
CLASSIFICATION OF EVIDENCE This study provides Class II evidence that in people with preclinical Alzheimer's disease, entorhinal hypometabolism identified by FDG-PET is predictive of subsequent cognitive decline.