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

Abstract

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.

Keywords: Huntington's disease; apathy subtypes; dimensional apathy scale.

FIG. 1

Self‐ and observer‐rated apathy on the AES and DAS across pre‐manifest HD and manifest‐HD groups. (A) Self‐ and observer‐rated apathy measured on the Dimensional Apathy Scale (DAS) ⁺ Indicates significant main effect between pre‐manifest and manifest groups. *Indicates significant interaction between Disease Stage and DAS Subscales. (B) Self‐ and observer‐rated apathy measured on the Apathy Evaluation Scale (AES). *Indicates significant main effect of Disease Stage. Error bars represent standard error.

FIG. 2

Self‐reported apathy on the AES and DAS across control, pre‐manifest HD and manifest‐HD groups. Top row (A and B) denotes self‐reported apathy on the AES and DAS across control and, pre‐manifest and manifest HD groups. (A) Control, pre‐manifest (pre‐HD) and manifest HD self‐reported apathy on the Apathy Evaluation Scale (AES). (B) Control, pre‐manifest (pre‐HD) and manifest HD self‐reported apathy scores on the Executive, Initiation and Emotional subscales of the Dimensional Apathy Scale (DAS). Bottom row (C and D) denotes the proportion of respondents with clinically high apathy across controls and, pre‐manifest and manifest HD groups. (C) Clinically relevant apathy defined as a DAS total score of ≥38. (D) Clinically relevant apathy on the DAS subscales defined as a score of ≥13 on Executive, ≥16 on Initiation, and ≥ 16 on Emotional, subscales. * P < 0.001. Error bars represent standard error.