Assessing the mobility of patients suffering from multiple sclerosis with mild neurological disability: reliability and responsiveness of the 2-minute walk test and the timed up-and-go test

Introduction: Limitations of mobility are frequent and disabling in persons with multiple sclerosis (pwMS), even when neurological disability is ‘mild’ (Expanded Disability Status Score (EDSS) ≤4). It is noteworthy to use high-quality measurement tools to monitor disease progression, to guide its management and monitor the efficacy of treatments. The timed up-and-go test (TUG) and the 2-minute walk test (2MWT) are valid to assess functional mobility and walking capacity, respectively, and widely used among pwMS. However, among those with mild disability, their reliability and responsiveness are unknown. Purpose: To determine the immediate and middle-term reliability and minimal detectable change (MDC95), as an index of responsiveness, of TUG and 2MWT in pwMS with mild neurological disability. Method: Thirty-six ambulatory pwMS (mean age:46; median EDSS:2.5; 30 women) performed consecutively two trials of 2MWT and of TUG. Twenty-five of these patients were assessed a second time, two weeks later, to assess middle-term reliability. Results were compared to normative values. Intraclass correlation coefficients (ICC, two-way random model, absolute agreement) were used to assess reliability. Bland-Altman method was used to explore agreement between measures. MDC95 at two weeks was calculated. Results: Mobility was impaired, in comparison to normative values (2MWT: -7.5% from normative distance; TUG: +30% from normative time). The immediate reliability was excellent for the 2MWT (ICC=0.98) and TUG (ICC=0.96). The difference between the second and the first trial of the 2MWT, performed 5 minutes apart, was correlated with the EDSS score (ρ=-0.41, p=0.01). Reliability at 2 weeks was excellent for 2MWT (ICC=0.93) and very good for TUG (ICC=0.82). MDC95 were respectively 22m (2MWT) and 1.79s (TUG). Conclusions: 2MWT is highly reliable and responsive in assessing the walking capacity of pwMS, while TUG has acceptable properties to assess functional mobility among these patients. These tools can be broadly used in clinical practice and research while evaluating so-called mildly disabled pwMS