Apathy in drug-naïve patients with incident Parkinson's disease: the Norwegian ParkWest study.

Apathy is a common behavioural problem in Parkinson's disease (PD), with important clinical consequences for patients and their families. However, little is known about apathy in early PD. We examined the frequency and clinical characteristics of apathy in 175 nondemented, drug-naïve patients with newly diagnosed PD and 165 control subjects matched for age, sex and education level in Western and Southern Norway. All participants underwent a comprehensive neurological, psychiatric and neuropsychological evaluation. Apathy was diagnosed based on Neuropsychiatric Inventory assessment and recently proposed consensus criteria. Apathy was found in 22.9% of the PD patients, of whom 37.5% had significant depressive symptoms, whereas none of the control subjects were apathetic. Apathy was significantly associated with male gender, higher depression scores and more severe motor symptoms, but was not associated with greater cognitive impairment. When excluding patients with significant depressive symptoms, apathy remained significantly associated with motor severity. Approximately 50% of the caregivers of patients with apathy reported the apathetic behaviour to be at least moderately distressing. The association between apathy and motor severity in our PD cohort suggests a common underlying pathophysiological mechanism. Future studies should explore the longitudinal effect of dopamine replacement therapy on apathetic behaviour in early PD. The relationship between apathy and male gender needs further study to be fully evaluated.