Assessment of apathy minimising the effect of motor dysfunctions in Parkinson's disease: a validation study of the dimensional apathy scale

Apathy is associated with motor symptoms in Parkinson's disease (PD); therefore, its evaluation could be influenced by motor disability. The Dimensional Apathy Scale (DAS) evaluates apathy excluding confounding effects of motor symptoms. The present study had three major aims: (a) to explore the psychometric properties of the DAS in non-demented PD patients; (b) to determine an optimal cut-off score of the DAS to identify apathetic PD patients; and (c) to determine a specific apathy profile in PD patients as compared to healthy controls (HC). One hundred and seven PD patients and 100 HC completed the DAS. To explore convergent and divergent validity of the DAS in PD, patients underwent the Apathy Evaluation Scale and tools for assessing depressive symptoms, anxiety and cognition. Clinical aspects were recorded. Receiver operating characteristic curve analyses were carried out to estimate the optimal cut-off score to identify clinically significant apathy. The DAS scores showed high internal consistency and good evidence for convergent and discriminant validity. Maximum discrimination between apathetic and non-apathetic patients was obtained with a cut-off score of 28.5 (total score range: 0-72 with higher score indicating more severe apathy). Comparison between PD and HC groups revealed significant differences on total DAS, behavioural/cognitive initiation and emotional subscales. The DAS is a valid and reliable tool to assess multidimensional apathy in PD, independently of severity of motor symptoms. Reduced initiation of thought and behaviour and emotional blunting characterised PD patients, without confounding effects of motor disability.