People with Amyotrophic Lateral Sclerosis (pwALS) have to make important decisions throughout their illness. Mental capacity is a legal term referring to the person’s ability to make a specific decision at a specific time. This comprises the ability to understand and retain information, weigh up pros and cons (reasoning), and communicate a decision. ALS is a spectrum disorder with an overlap with frontotemporal dementia (ALS-FTD), where up to 50% of pwALS experience changes in cognition and behaviour, and around 15% develop ALS-FTD. This includes impairments in executive functions, language, social cognition, and apathy. However, it is currently unknown whether these changes have an impact on pwALS’s mental capacity to consent to medical treatments. This study aimed to explore if mental capacity to consent to medical treatments (gastrostomy/feeding tube) is affected in pwALS and to investigate the relationship to specific cognitive and behavioural impairments in ALS.

14 pwALS and 14 controls, matched in age, gender, and level of education, completed an adapted version of the MacArthur Competence Assessment Tool for Treatment (MacCAT-T) for assessing mental capacity to consent to a gastrostomy and the Edinburgh Cognitive and Behavioural ALS Screen (ECAS). The ECAS is a brief assessment of executive functions, language, verbal fluency, memory and visuospatial skills that has been validated in ALS and FTD. 11 relatives/friends of pwALS completed the ECAS semi-structured interview to assess behaviour abnormalities found in FTD.

PwALS scored significantly worse than controls in mental capacity (MacCAT-T total score), particularly in the understanding and retaining information component and in ECAS total score. PwALS also presented a significant difference in the amount and type of abnormal behaviours. 4/14 pwALS had cognitive impairment, 6/11 had behavioural impairment and 2/11 had both. In relation to scores in the MacCAT-T, 5/14 had difficulties understanding and retaining information, 6/14 struggled weighing up pros and cons and 2/14 had difficulties with both, which resulted in 9/14 pwALS with impaired mental capacity for the gastrostomy decision. All participants with impaired mental capacity also had impairments in either cognition (4/14), behaviour (4/11) or both (1/11). ECAS total score (β=0.56, p=<0.05), language (β=0.53, p=0.05) and memory (β=0.68, p=<0.01) were the only significant variables predicting mental capacity (MacCAT-T total score). ECAS total score (β=0.70, p=<0.01), executive functions (β=0.63, p=<0.05), language (β=0.58, p=<0.05) and memory (β=0.71, p=<0.01) predicted the reasoning component of mental capacity. None of the variables tested predicted the understanding component of the mental capacity assessment.

These preliminary findings suggest that some pwALS (64% of our sample) may lack the capacity to make specific treatment decisions, with the ability to understand and retain information being the most impaired. Some pwALS may also present difficulties weighing up pros and cons. The results also suggest that cognitive impairment, particularly in executive functions, language, and memory, may be more associated with impaired mental capacity than with behavioural impairment. Mental capacity assessments should be considered when discussing treatment options with pwALS and support should be provided to facilitate understanding and weighing up complex information about treatments.