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 >or=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.