Abstract
Apathy and impulsive behaviour co-occur in Huntington's disease (HD), but these debilitating behavioural syndromes are multidimensional constructs, raising the question of which specific dimensions drive this relationship and the stability of the co-occurring dimensions across time. People with HD and controls completed multidimensional apathy and impulsive behaviour scales at baseline and 1-year follow-up. A principal component analysis was performed on pooled data (n = 109) to identify components and factor loadings of subscales. Linear mixed models were used to examine differences in components between groups and timepoints. Three meaningful components emerged. Component 1 comprised positive loading for dimensions of apathy and impulsive behaviour pertaining to goal-directedness, namely attention, planning, initiation, and perseverance. In contrast, other dimensions of apathy and impulsive behaviour loaded onto components two and three in opposite directions. People with HD only scored worse than controls on the goal-directedness component. All components remained stable over time and closely resembled factors from the five-factor personality model. Component 1 mapped onto the factor conscientiousness, component 2 to extraversion, and component 3 to neuroticism. The clinical overlap between apathy and impulsive behaviour in HD relates to goal-directedness, whilst other dimensions of these constructs did not overlap.