Identifying a Minimally Important Change Threshold for The Multiple Sclerosis Walking Scale-12 (MSWS-12)

Background: The 12-question Multiple Sclerosis (MS) Walking Scale (MSWS-12v1) is a widely-used patient-reported outcome (PRO) measure of walking ability in MS. Objective: To estimate the magnitude of an important change in MSWS-12v1 scores for the interpretation of meaningful subject-level improvements across a 6-month trial of MS patients with walking disability. Methods: MOBILE was a 6-month exploratory study assessing fampridine’s effect on walking ability in 132 people with MS. Three PRO measures assessed walking ability: MSWS-12v1, EuroQol 5-Dimension-5 Level (EQ-5D-5L) mobility question, and a patient global impression of change (PGIC) in overall walking ability. Pre-specified anchor- and distribution-based analyses estimated the MSWS-12v1 change scores representing an important change for participants. Results were triangulated to propose a single best value indicating meaningful improvement. Results: Using Baseline to Week 2 through Week 24 change scores, anchor-based analyses demonstrated mean and median improvements of 5.2-6.6 (PGIC) and 9.7-13.4 (EQ-5D-5L mobility) points on the MSWS-12v1 indicated meaningful improvements. The distribution-based estimate was 6.8 points. Triangulation across the results suggested an 8-point reduction in MSWS-12v1 score represents an important subject-level change in these participants. Conclusion: In similar MS clinical trials, an 8-point improvement on the MSWS-12v1is a reasonable estimate of meaningful improvement in walking ability.