Differentiating the Frontal Presentation of Alzheimer's Disease with FDG-PET

Abstract

Alzheimer's disease (AD) can present with behavioral changes with this syndrome described as frontal variant AD (FvAD). Excess frontal pathology may explain this presentation. Neuroimaging with fluoro-deoxy-glucose positron emission tomography (FDG- PET) can be used to examine the effects of pathology in FvAD. We administered an assessment scale for frontal behavioral impairment, the Frontal Behavioral Inventory (FBI), to 53 patients with AD. Scores in the top quartile were defined as FvAD. FDG- PET was analyzed in 8 frontal regions. The Z (SD) score for metabolism was significantly higher (indicating greater hypometabolism) in the FvAD group than the remaining AD group for combined left and right orbitofrontal regions (2.64 (SD 0.99) versus 2.11 (1.22), p < 0.03)) and combined left and right medial frontal regions (2.38 (0.63) versus 1.82 (0.88) p < 0.003) but insignificantly different in combined lateral frontal and superior frontal regions. Statistical parametric mapping revealed these frontal regions to be the only brain regions with significantly different metabolism between the FvAD and the remainder of the AD groups. Medial and orbital frontal hypometabolism is greater in AD patients presenting with more frontal/behavioral features, likely reflecting a greater pathological load in these brain regions in FvAD patients. These frontal regions may be more linked to behavioral features than other frontal brain regions.