Delirium is more common and associated with worse outcomes in Parkinson’s disease compared to older adult controls: results of two prospective longitudinal cohort studies

Abstract Background Inpatient prevalence of Parkinson’s disease (PD) delirium varies widely across the literature. Delirium in general older populations is associated with adverse outcomes, such as increased mortality, dementia, and institutionalisation. However, to date there are no comprehensive prospective studies in PD delirium. This study aimed to determine delirium prevalence in hospitalised PD participants and the association with adverse outcomes, compared to a control group of older adults without PD. Methods Participants were hospitalised inpatients from the ‘Defining Delirium and its Impact in Parkinson’s Disease’ and the ‘Delirium and Cognitive Impact in Dementia’ studies comprising 121 PD participants and 199 older adult controls. Delirium was diagnosed prospectively using the Diagnostic and Statistical Manual of Mental Disorders 5th Edition criteria. Outcomes were determined by medical note reviews and/or home visits 12 months post hospital discharge. Results Delirium was identified in 66.9% of PD participants compared to 38.7% of controls (p 0.001). In PD participants only, delirium was associated with a significantly higher risk of mortality (HR = 3.3 (95% confidence interval CI = 1.3–8.6), p = 0.014) and institutionalisation (OR = 10.7 (95% CI = 2.1–54.6), p = 0.004) 12 months post-discharge, compared to older adult controls. However, delirium was associated with an increased risk of developing dementia 12 months post-discharge in both PD participants (OR = 6.1 (95% CI = 1.3–29.5), p = 0.024) and in controls (OR = 13.4 (95% CI = 2.5–72.6), p = 0.003). Conclusion Delirium is common in hospitalised PD patients, affecting two thirds of patients, and is associated with increased mortality, institutionalisation, and dementia. Further research is essential to understand how to accurately identify, prevent and manage delirium in people with PD who are in hospital.