F-FDG PET in detection of primary age-related tauopathy (PART) - Is there a role? Insights from an imaging-pathology correlation study.

Introduction: Primary age-related tauopathy (PART) is defined by neurofibrillary tangles (NFTs) with absent-minimal amyloid beta (Aβ) plaques. Currently, definitive diagnosis of PART occurs with autopsy. This study investigated whether [F]fluorodeoxyglucose positron emission tomography (FDG-PET) could detect PART-related metabolic changes and assessed the impact of common co-pathologies.

Methods: We performed a retrospective cross-sectional study of 88 individuals (mean age 85.6) with autopsy-confirmed PART (Braak I to IV; Thal phases 0 to 2) who underwent ante mortem FDG-PET. Visual ratings and standardized uptake value ratios (SUVRs) were analyzed in medial and lateral temporal lobes, inferior temporal pole, precuneus, and posterior cingulate regions.

Results: Medial temporal hypometabolism was observed in PART, in the presence of co-pathologies. Argyrophilic grain disease and TAR DNA-binding protein 43 were associated with greater hypometabolism (p < 0.01). Lewy body disease affected parietal regions.

Discussion: FDG-PET reveals that PART-related hypometabolism occurs when co-pathologies are present, but PART alone appears to have minimal effect on medial temporal lobe hypometabolism.

Highlights: FDG-PET hypometabolism worsens with Braak NFT stage. FDG-PET detects mild lateral temporal lobe hypometabolism in PART alone. PART alone has a minimal effect on medial temporal lobe hypometabolism. Medial temporal hypometabolism is worse in PART with TDP-43 and especially AGD. The presence of LBD contributes to parietal hypometabolism on FGD-PET in PART.