Apathy and depression: separate factors in Parkinson's disease.

The objective of this study was to test the hypothesis that apathy and depression are dissociable in Parkinson disease (PD) by conducting a confirmatory factor analysis (CFA) of items from two commonly used mood scales. A total of 161 non-demented PD patients (age=64.1; +/- 68.4 years) were administered the Apathy Scale and the Beck Depression Inventory-II. Items were hypothesized to load onto four factors: (1) an apathy factor representing loss of motivation, (2) dysphoric mood factor representing sadness and negativity, (3) loss of interest/pleasure factor representing the features common to both apathy and depression, and (4) a somatic factor representing bodily complaints. Results indicated a good fit for the overall CFA model, chi(2) (128, N=146) = 194.9; p<.01. RMSEA was .060 (p=.16). The four-factor model was significantly better than all alternative nested models at p<.001, including an overarching single factor model, representing "depression." Results support the concept that apathy and depression are discrete constructs. We suggest a "factor based" scoring of the Apathy Scale and Beck Depression Inventory-II that disentangles symptoms related to apathy, depression, overlapping symptoms, and somatic complaints. Such scoring may be important in providing useful information regarding differential treatment options. (JINS, 2011, 17, 1058-1066)