Frontal Hypometabolism in Neurocognitive Disorder with Behavioral Disturbance

Criteria for the behavioral variant of frontotemporal dementia (bvFTD) include decreased frontal metabolism. ¹⁸F-FDG PET was used to investigate whether patients with the behavioral variant of neurocognitive disorder (bvNCD) who did not fulfill 3 bvFTD criteria had the characteristic brain metabolic pattern. Methods: Patients were referred from the memory clinic to the nuclear medicine department for differential diagnosis of neurocognitive disorder with dysexecutive syndrome and predominant mild frontal atrophy. When only 2 bvFTD criteria were met, patients were classified into 2 groups before ¹⁸F-FDG PET: probable bvFTD (n = 25) or bvNCD (n = 27). Results: Voxel-based and multivariate partial least-squares analyses of ¹⁸F-FDG PET did not show significant between-group difference at inclusion. After 4.8 y of follow-up, most patients with probable bvFTD received the same diagnosis, 3 remained stable, and 1 participant was given a psychiatric diagnosis. Five patients with bvNCD fulfilled the criteria for probable bvFTD at a 4.4-y mean follow-up, whereas 2 participants remained stable and 3 received alternative neurologic or psychiatric diagnoses. When initial ¹⁸F-FDG PET findings were compared between groups stratified at follow-up (26 bvFTD vs. 17 bvNCD), there was a trend (P < 0.001, uncorrected) for lower prefrontal metabolism with relatively preserved premotor metabolism in bvFTD than in bvNCD. Twelve bvNCD participants had neuropsychologic testing before inclusion. They all presented executive dysfunction and normal visuospatial performance, and most (n = 9) had memory-encoding impairment. Conclusion: Frontal hypometabolism was observed in a dysexecutive presentation of frontal neurodegenerative disorder (bvNCD) that did not fulfill all clinical criteria for bvFTD.