Prevalence and clinical correlates of apathy in Parkinson's disease: a community-based study.

The objective of this study was to examine the prevalence and clinical correlates of apathy in a population-based sample of patients with Parkinson's disease (PD) and to assess whether apathy may present as a primary behavioural disturbance independent from depression and cognitive impairment. A total of 232 patients derived from an epidemiological study of PD in Rogaland county, Western Norway, completed a comprehensive evaluation of motor, cognitive, and depressive symptoms. Apathy was assessed with the motivation/initiative item of the Unified Parkinson's Disease Rating Scale. The majority of the population had mild to moderate PD with mean disease duration of 9.1+/-5.7 years. Apathy was diagnosed in 38% of the 232 patients. In 11% of the total sample apathy coexisted with depression and dementia, whereas 10% had apathy and depression without dementia, 6.5% apathy and dementia without depression, and 9% were apathetic without dementia or depression (data missing in 1.5% patients). Apathy was significantly associated with higher depression scores, lower cognitive functioning, and more severe motor symptoms. When excluding patients with depression, dementia, cognitive impairment with no dementia (population-based age- and education-corrected norms for the Mini-Mental State Examination), and those using psychotropic medication, 5% of the 232 patients had apathy. In conclusion, our study shows that apathy is common in the general PD population, may present as an independent behavioural disorder, and suggests that apathy in PD may be related to dysfunction of the nigro-striatal pathway or that brain pathology underlying apathy and progression of motor symptoms develops in parallel.