The relationship between hallucinations and FDG-PET in dementia with Lewy bodies

Visual hallucinations are common in dementia with Lewy bodies (DLB), although their etiology is unclear. This study aimed to investigate the relationship between severity and frequency of hallucinations and regional brain glucose metabolism. We performed brain FDG-PET scanning on 28 subjects with DLB (mean age 76). The neuropsychiatric index (NPI) was used to assess frequency and severity of hallucinations. We used the SPM package to investigate voxelwise correlations between NPI hallucination score (severity x frequency) and FDG uptake relative to the cerebellum. There was a bilateral medial occipital region where reduced FDG was associated with increased hallucination severity and frequency. We conclude that the reduced occipital metabolism frequently seen in DLB is associated with frequency and severity of visual hallucinations. Further studies are required to investigate whether this is the result of deficits in top-down or bottom-up visual processing pathways.