Multidimensional Apathy: The Utility of the Dimensional Apathy Scale in Huntington's Disease

Background: Apathy is a disorder of motivation common to Huntington's disease (HD). Recent conceptual frameworks suggest that apathy is not unitary but consists of discrete subtypes (“dimensions”). Which of the proposed dimensions are preferentially affected in HD, and how these dimensions evolve with disease progression is unknown. Objectives: The Dimensional Apathy Scale (DAS) separates apathy into Executive, Initiation and Emotional subscales. Using the DAS, we aimed to: 1) Determine the apathy subtypes prevalent in HD; 2) Compare the DAS against a unitary measure of apathy (Apathy Evaluation Scale, AES); 3) Assess the reliability of self- and observer-ratings; and 4) Determine the relationship between the DAS, and disease burden, total functional capacity (TFC) and the AES. Method: Fifty pre-manifest, 51 manifest-HD, 87 controls, and 50 HD-observers completed the DAS, AES, and TFC. Results: Manifest-HD participants had the highest levels of apathy across all dimensions (30.4% on Executive subscale, 34.8% on Initiation subscale, and 15.2% on Emotional subscale), relative to pre-manifest and control participants. Self- and observer-ratings on the DAS did not differ. Hierarchical regressions across the entire gene-expanded sample showed that scores on the Initiation subscale correlated with AES scores; higher Executive subscale scores were related to higher disease burden; and Emotional subscale scores with lower total functional capacity. Conclusions: In this first study of the DAS in HD, manifest-HD participants were more apathetic than pre-manifest and control participants across all apathy subtypes. The DAS may be a useful tool for measuring different aspects of apathy in people with HD.