Brain metabolic patterns in patients with suspected non-Alzheimer's pathophysiology (SNAP) and Alzheimer's disease (AD): is [¹⁸F] FDG a specific biomarker in these patients?

Purpose: The present study was conducted to compare the pattern of brain [¹⁸F] FDG uptake in suspected non-Alzheimer's pathophysiology (SNAP), AD, and healthy controls using 2-deoxy-2-[¹⁸F]fluoroglucose ([¹⁸F] FDG) positron emission tomography imaging. Cerebrospinal fluid (CSF) biomarkers amyloid-β1-42 peptide (Aβ1-42) and tau were used in order to differentiate AD from SNAP.

Methods: The study included 43 newly diagnosed AD patients (female = 23; male = 20) according to the NINCDS-ADRDA criteria, 15 SNAP patients (female = 12; male =3), and a group of 34 healthy subjects that served as the control group (CG), who were found to be normal at neurological evaluation (male = 20; female = 14). A battery of neuropsychological tests was administrated in AD and SNAP subjects; cerebrospinal fluid assay was conducted in both AD and SNAP as well. Brain PET/CT acquisition was started 30 ± 5 min after [¹⁸F] FDG injection in all subjects. SPM12 [statistical parametric mapping] implemented in MATLAB 2018a was used for the analysis of PET scans in this study.

Results: As compared to SNAP, AD subjects showed significant hypometabolism in a wide cortical area involving the right frontal, parietal, and temporal lobes. As compared to CG, AD subjects showed a significant reduction in [¹⁸F] FDG uptake in the parietal, limbic, and frontal cortex, while a more limited reduction in [¹⁸F] FDG uptake in the same areas was found when comparing SNAP to CG.

Conclusions: SNAP subjects show milder impairment of brain [¹⁸F] FDG uptake as compared to AD. The partial overlap of the metabolic pattern between SNAP and AD limits the use of [¹⁸F] FDG PET/CT in effectively discriminating these clinical entities.