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

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.

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).

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.

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.