Comparing PET and MRI Biomarkers Predicting Cognitive Decline in Preclinical Alzheimer Disease

Neurology. 2021 May 5;96(24):e2933-e2943. doi: 10.1212/WNL.0000000000012108. Online 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.