Visual Hallucination and Pattern of Brain Degeneration in Parkinson's Disease

The incidence of visual hallucination (VH) increases with Parkinson's disease (PD) progression, and its development is thought to be related to a specific neurodegenerative process in PD. This study aimed to reveal brain degeneration related to VH in PD by analyzing neuroimaging data obtained from patients in their different stages of PD.

Data from 48 PD patients - 21 nondemented without VH (PNV group), 10 nondemented with VH (PV group), and 17 demented with VH (PVD group) - and 30 age-matched healthy controls (HC group) were analyzed. Voxel-based morphometry and tract-based spatial statistics were conducted. Previous magnetic resonance volumetric studies on VH in PD were collectively reviewed.

The PV group showed gray matter atrophy in the right inferior parietal lobule and supramarginal gyrus compared with the HC and PNV groups. The PVD group showed a wider range of gray matter atrophies in the temporo-parieto-occipital regions than those in the PV group. White matter changes seemed to be an earlier event than gray matter changes. Fractional anisotropy values diffusely decreased in all three PD subgroups compared with the HC group without significant differences between the PD subgroups. Mean diffusivity was not different between the PNV and HC groups but increased in the parieto-temporal region in the PV group and increased diffusely in the PVD group, additionally including the fronto-occipital regions. A review of previous studies supported our observations.

Gray matter degenerations from the parieto-temporal junction to the parieto-occipital and temporo-occipital regions may be responsible for VH on the typical timeline of PD progression.