Caregiver report of apathy predicts dementia in Parkinson's disease.

Introduction: Apathy is a common, troublesome symptom in Parkinson's disease (PD). However, little is known about its relationship with long-term cognition. We sought to determine if a caregiver-reported apathy measure predicts the development of PD dementia.

Methods: Non-demented PD patients were recruited as part of a longitudinal study of cognition. Demographics, medications, Dementia Rating Scale-2, Unified Parkinson's Disease Rating Scale, Geriatric Depression Scale and the Neuropsychiatric Inventory-Questionnaire (NPI-Q) ratings were obtained. Apathy was defined as an NPI-Q apathy score ≥1. Participants were evaluated annually with cognitive and functional assessments until the end of the study period or a physician consensus diagnosis of dementia was assigned. Cox proportional hazard models were used to assess the effects of baseline apathy on dementia development while controlling for other clinical and demographic factors.

Results: Of 132 PD patients 12.1% (N = 16) scored in the apathetic range at baseline. A total of 19.6% (N = 26) individuals developed dementia over the course of the study, 8 of whom (30.8% of future dementia patients) had baseline apathy. In bivariate analyses baseline apathy, older age, and worse cognitive, motor, and depressive symptom scores predicted the development of dementia. In a multivariate analysis the predictive effects of baseline apathy were still significant (HR = 3.56; 95% CI = 1.09-11.62; p = 0.04).

Conclusions: A simple, caregiver-reported measure of apathy is an independent predictor of progression to dementia in PD. This highlights the importance of apathy as a clinical characteristic of PD and could prove useful for the prediction of future dementia.