Validity of minimal clinically important difference values for the multiple sclerosis walking scale-12?

Background and Objective: Minimal clinically important difference (MCID) values of 4 and 6 points have been proposed for interpreting meaningful change in Multiple Sclerosis Walking Scale-12 (MSWS-12) scores. This study examined the validity of those MCID values based on capturing corresponding changes in other walking outcomes in persons with multiple sclerosis (MS). Methods: On 2 occasions separated by 6 months, 82 persons with MS completed the MSWS-12, timed 25-ft walk (T25FW), 6-min walk (6MW), and gait analysis, and then wore an accelerometer over a 7-day period. We generated change scores for the MSWS-12 and formed groups of stable, worsened, and improved perceived walking based on both 4- and 6-point changes. The groups were compared for corresponding changes in other walking measures over time using mixed-model ANOVAs. Results: The mixed-model ANOVAs did not identify statistically significant group-by-time interactions on the T25FW (p = 0.98 and p = 0.67), the 6MW (p = 0.89 and p = 0.72), gait (p = 0.54 and p = 0.21), or accelerometry (p = 0.40 and p = 0.68) for MCID values of 4- or 6-point changes in MSWS-12 scores. Conclusions: We did not confirm that MCID values of 4 and 6 points for the MSWS-12 correspond with changes in performance, gait, and free-living assessments of walking in MS.