Objective To explore the multidimensionality of apathy in ALS, To validate the Dimensional Apathy Scale (DAS) in ALS patients and their carers.

Method This was a Scotland- wide questionnaire based study where 83 ALS patients, 75 of their informants and 83 gender-age-education level matched controls were recruited. Control, patient and carer participants completed a standard apathy scale-the Apathy Evaluation scale (AES), the Geriatric Depression Scale-Short form (GDS-15) and the DAS, which is composed of 3 subscales assessing Executive, Emotional and Initiation apathy subtypes. The ALS Functional Rating Scale-Revised (ALSFRS-R) scores were acquired to measure disease related disability.

Results ALS patient (self rated) and carer rated comparison on the DAS showed no significant difference on each of the subscales. There was a significant between-subscale dissociation for both the patients and their carers, F(2,296)=160.30, p<.001. ALS patient (self rated) and control responses to the DAS subscales were found to be significantly different, F(2,328)=13.86, p<.001. Further post-hoc t-tests showed that patients (M=12.5, SD=5.1), compared to controls (M=10.2, SD=4.3), were significantly more impaired on the Initiation subscale, t(64)=3.22, p<.01. Additionally, controls were slightly more Emotionally apathetic (M=8.9, SD=3.2) compared to patients (M=7.7, SD=3.3), t(164)=2.28, p<.05. The psychometrics of the DAS were found to be favourable. The Cronbach's standardized alpha values were high, with the carer (0.90) being slightly higher than the patient (0.86). DAS subscales correlated more highly with the AES compared to the GDS-15, again with that of the carers being slightly higher and better discriminating Emotional apathy against depression. The ALSFRS-R was not significantly correlated with any of the DAS subscales.

Conclusion Using a multidimensional approach to apathy assessment, our study determined that ALS patients showed an apathy profile, characterised by difficulties in initiation of behaviour and cognition. The DAS was found to be a valid and reliable measurement of the dimensions of apathy, independent of disease related disability. Future research will investigate the relationship of these apathy dimensions and cognitive functioning in ALS and further validate the DAS in other neurodegenerative populations.