Validity Of MCID Values For The Multiple Sclerosis Walking Scale-12

Background: The Multiple Sclerosis Walking Scale-12 (MSWS-12) has increasingly been included in research involving multiple sclerosis (MS) patients based on the strength of its psychometric evidence as a measure of walking impairment. To that end, researchers have developed minimal clinically important difference (MCID) values of between 4 and 6 points for interpreting meaningful change in MSWS-12 scores. The MCID values have yet to be validated with changes in walking and gait outcomes in prospective, observational research.

Objectives: This study examined the validity of existing MCID values for the MSWS-12 based on capturing corresponding changes in performance, gait, and free-living measures of walking over a six-month period in persons with MS.

Methods: On two occasions separated by six months, 82 persons with MS completed the MSWS-12 along with the timed 25-foot walk (T25FW), 6-minute walk (6MW), four walking trials on an electronic walkway as an assessment of gait, and wore an accelerometer on a belt around the waist over a 7-day period. We generated change scores for the MSWS-12, and then formed groups of stable (e.g., change within ± 4 points), worsened (e.g., change ≥ + 4 points), and improved (e.g., change ≥ − 4 points) perceived walking impairment based on 4 and 6 point changes in MSWS-12 scores. The groups were then compared for changes in other outcome measures over time using mixed model ANOVA.

Results: The intraclass correlation coefficient (ICC) for MSWS-12 scores (ICC = .93) and results of a paired samples t-test (p = .53) indicated group-level stability of scores over the 6-month period. Nevertheless, there were 34 persons who worsened, 29 who improved, and 19 who were stable over the 6-month period based on an MCID of 4. There were 24 persons who worsened, 24 who improved, and 34 who were stable over the 6-month period based on an MCID of 6. The mixed model ANOVA did not identify statistically significant group by time interactions for T25FW (p’s = .98 & .67, respectively), 6MW (p’s = .89 & .72, respectively), gait (p’s = .54 & .21, respectively), or free-living accelerometry (p’s = .40 & .68, respectively) with either the 4 or 6 point changes in MSWS-12 scores.  

Conclusions: Such results did not confirm the MCID values of between 4 and 6 points for the MSWS-12 as capturing corresponding changes in performance, gait, and free-living assessments of walking in MS.