Multidimensional apathy in neurodegenerative disease
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Apathy is characterised by a lack of motivation towards goal directed behaviour and is a symptom of various neurodegenerative diseases. There are various tools that can be used to assess apathy but a caveat of these is that they usually assess it as a unidimensional concept. Apathy has been recognised to have a multidimensional substructure. The Dimensional Apathy Scale is the only comprehensive measure designed to quantify neurobiologically-based subtypes, called Executive, Emotional and Initiation apathy. The first aim of this study was to explore multidimensional apathy, and its associations with demographic variables, in healthy, community dwelling adults. Secondly, multidimensional apathy was explored in neurodegenerative diseases, specifically Amyotrophic lateral sclerosis (ALS), Parkinson’s disease (PD) and Alzheimer’s disease (AD). For each disease group, the validity and reliability of both the self rated and carer rated DAS were also determined. Finally, the association between specific apathy subtype impairments and executive dysfunction was explored in ALS patients. Four hundred healthy community dwelling adults, eighty-three ALS patients (seventy-five carers), thirty-four PD patients (thirty carers) and forty-nine AD patients (eighty-nine carers) were recruited for the questionnaire study. In the healthy community dwelling adults, Executive apathy decreased with age, whereas Emotional increased with age. Gender differences were also shown with higher apathy in males on Emotional apathy. There were also employment differences, in that Executive apathy was higher in unemployed individuals compared to those who were employed. Emotional apathy showed difference in type of employment, where full time employed individuals were significantly more apathetic than those employed part time. These findings were taken into account in selecting the appropriate control samples to match our patient groups. In the patient groups, ALS patients were found to be significantly more impaired on the Initiation subscale when compared to controls. Furthermore, Initiation apathy was found to be the most frequent impairment above abnormality cut-off on the carer rated DAS. PD patients were significantly more impaired on Executive and Initiation apathy when compared to controls. These two subscales were most frequently above abnormality cut-off in the carer rated DAS. Finally, AD patients were significantly more impaired on all subscales when compared to controls and, on the carer rated DAS, global impairment over all subscales was most often reported as above abnormality cut-off. Additionally in AD, there was a significant disparity between carer and patient ratings on Executive and Initiation apathy, indicating patients’ impaired awareness. When comparing patient groups, there was a significant difference between carer rated apathy subtype impairments for each patient group. Validity and reliability of the DAS was found to be robust when compared to standard measures of apathy and depression. In the experimental study, a sample of ALS patients (and their carers) and healthy controls (and their informants) were recruited to complete a battery of neuropsychological tests, the DAS, other apathy and depression measures. ALS patients were impaired on tasks of executive functioning when compared to controls. Furthermore, apathy subtype deficits were associated with executive dysfunction in ALS. In conclusion, apathy is a multidimensional concept that manifests in different subtype profiles dependent on neurodegenerative disease. This has further implications for understanding and assessment of cognitive dysfunction and neuropsychiatric symptoms, such as apathy, in ALS and other neurodegenerative disease patient groups.