Occurrence and risk factors for apathy in Parkinson disease: a 4-year prospective longitudinal study

Background: Apathy is a common but under-recognised behavioural disorder associated with depression and cognitive impairment in patients with Parkinson disease (PD). However, the longitudinal course of apathy in PD has not been studied. Objective: To examine the occurrence of and risk factors for apathy over time in a representative sample of patients with PD. Methods: A sample of 139 patients was drawn from a population-based prevalence study of PD in Rogaland County, Western Norway. Apathy was measured with the Neuropsychiatric Inventory, using a composite score >= 4 to indicate clinically significant apathy. Additional measurements included standardised rating scales for parkinsonism, depression and cognitive impairment. A follow-up evaluation was carried out in 79 patients (78.2% of the survivors) 4 years later. Results: Of the 79 patients included in this study, 29 patients (36.7%) had never had apathy, 11 (13.9%) had persistent apathy, and a further 39 (49.4%) developed apathy during follow-up. At follow-up, patients with apathy were more frequently depressed and demented than never-apathetic patients. Dementia at baseline and a more rapid decline in speech and axial impairment during follow-up were independent risk factors for incident apathy. Conclusions: Apathy is a persistent behavioural feature in PD with a high incidence and prevalence over time. Progression of motor signs predominantly mediated by non-dopaminergic systems may be a useful preclinical marker for incident apathy in PD.