Executive function but not episodic memory decline associated with visual hallucinations in Parkinson's disease.

INTRODUCTION: Visual hallucinations (VH) have a significant impact on quality of life for people with Parkinson's disease (PD). A major reason for this is the well-established link with cognitive impairment, but there is still a need for more longitudinal studies examining the specific cognitive domains which may be affected. The aim of this study was to profile decline in cognition associated with VH in a cohort of 69 individuals with PD over 1 year.

METHOD: Visual hallucinations assessments were carried out every 3 months. Executive function and episodic memory were assessed at baseline and 1 year. All evaluations were performed via phone interviews. The presence or absence of VH was categorized based on the entirety of the year's data (i.e., no episodes and >0 episodes). We also defined a persistent VH group who had VH present at more than one time point and compared these with a no-VH group and a group with transient VH (i.e., only one episode).

RESULTS: Linear mixed-effect models showed that VH were associated with more rapid overall cognitive decline (-0.26, t = -2.39, p = .02), which was driven by executive function (-0.28, t = -2.48, p = .02). Persistent VH were associated with decline in executive function (-0.33, t = -2.4, p = .02), while no relationship was found for non-persistent VH, suggesting that persistent VH be the major driver of this relationship.

CONCLUSION: This finding brings greater clarity to the relationship between cognitive decline and VH in PD. Future research should examine the robustness of this phenotype for biomarkers studies and treatment interventions.