Categorising Visual Hallucinations in Early Parkinson's Disease

Background: Visual hallucinations (VHs) are common in Parkinson's disease (PD), with prevalence ranging from 27-50% in cross-sectional cohorts of patients with well-established disease. However, minor hallucinations may occur earlier in the disease process than has been previously reported. Objective: We sought to categorise VHs in a cohort of newly diagnosed PD patients and establish their relationship to other clinical features. Methods: Newly diagnosed PD participants (n = 154) were recruited as part of the Incidence of Cognitive Impairment in Cohorts with Longitudinal Evaluation in PD (ICICLE-PD) study. Participants completed the Movement Disorders Society Unified Parkinson's Disease Rating Scale (MDS-UPDRS III), Montreal Cognitive Assessment (MoCA) and Parkinson's Disease Questionnaire (PDQ-39) to assess motor severity, cognition and quality of life (QoL), respectively. VHs were classified using the North East Visual Hallucinations Inventory. Hierarchical regression was used to build predictive models of motor severity, QoL and cognition. Results: 22% (n = 34) of participants experienced recurrent VHs with minor VHs being most frequently reported (64.7% of hallucinators). Complex VHs were present in 32.4% of hallucinating participants. Linear regression showed VHs predicted poorer PDQ-39 and MoCA scores (beta = 0.201, p = 0.006 and beta = -0.167, p = 0.01, respectively) but not motor severity (p > 0.05). Conclusions: Over a fifth of people with newly diagnosed PD reported recurrent VHs; minor hallucinations were the most common, although a small proportion reported complex VHs. Recurrent VHs were found to be a significant independent predictor of cognitive function and QoL but not motor severity. Our findings highlight the importance of screening for VHs at diagnosis.