Quantifying metabolic decrement in brain FDG-PET of a complex frontotemporal dementia case

Diagnosis of behavioral variant frontotemporal dementia (bvFTD) in its initial stages can be supported by brain [18F] fluorodeoxyglucose-positron emission tomography (FDG-PET). The routine use of semi-quantitative analyses in FDG-PET is formally recommended. However, the longitudinal changes observed in sequential FDG-PETs scans throughout neurodegenerative diseases remain insufficiently understood. In this case, a bvFTD phenocopy remained clinically stable for nine years before exhibiting functional decline consistent with bvFTD. Hypometabolism compatible with bvFTD was observed only on the third FDG-PET, performed six years after the first. Retrospective analysis revealed that the second FDG-PET had already shown a decline in metabolism in areas typically affected by bvFTD compared to the first scan. During the period of clinical stability, individual exams were insufficient to confirm the diagnosis. However, the metabolic decrease between the first and second scans may have indicated subclinical progression. The decline in semi-quantitative FDG-PET scores could represent a useful diagnostic tool in bvFTD.