The Use of Digital Devices to Monitor Physical Behavior in Motor Neuron Disease: Systematic Review

Background: Motor neuron disease (MND) is a progressive and incurable neurodegenerative disease. The Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R) is the primary clinical tool for assessing disease severity and progression in MND. However, despite its widespread use, it does not adequately capture the extent of physical function decline. There is an urgent need for sensitive measures of disease progression that can be used to robustly evaluate new treatments. Measures of physical function derived from digital devices are beginning to be used to assess disease progression. There is value in establishing a consensus approach to standardizing the use of such devices. Objective: We aimed to explore how digital devices are being used to quantify free-living physical behavior in MND. We evaluated the feasibility and assessed the implications for monitoring physical behavior for future clinical trials and clinical practice. Methods: Systematic searches of 4 databases were performed in October 2023 and June 2024. Peer-reviewed English-language articles (including preprints) that examined how people living with MND used digital devices to assess their free-living physical behavior were included. Study reporting quality was assessed using a 22-item checklist (maximum possible score=44 points). Results: In total, 12 articles met the inclusion criteria for data extraction. All studies were longitudinal and observational in design, but data collection, analysis, and reporting protocols varied. Quality assessment scores ranged between 19 and 40 points. Sample sizes ranged between 10 and 376 people living with MND at baseline, declining over the course of the study. Most studies used an accelerometer device worn on the wrist, chest, hip, or ankle. Participants were typically asked to continuously wear devices for 1 to 8 days at 1- to 4-month intervals, with studies running for 12 weeks to 24 months. Some studies asked participants to wear the device continuously for the full duration. Studies derived traditional end points focusing on duration, intensity, and frequency of physical activity or nontraditional end points focusing on features of an individual’s movement patterns. The correlation coefficients (r) between physical behavior end points and ALSFRS-R ranged from 0.31 to 0.78. Greater monitoring frequencies and improved end point sensitivity were shown to provide smaller sample size requirements and shorter durations for hypothetical clinical trials. People living with MND found using devices acceptable and reported a low burden. Adherence assessed in 8 (67%) studies was good, ranging from approximately 86% to 96%, with differences evident between wear locations. The perspectives of other end users and implications on clinical practice were not explored. Conclusions: Remote monitoring of free-living physical behavior in MND is in its infancy but has the potential to quantify physical function. It is essential to develop a consensus statement, working toward agreed and standardized methods for data collection, analysis, and reporting.