Cognitive processing speed has minimal influence on the construct validity of Multiple Sclerosis Walking Scale-12 scores

Abstract

BackgroundThe Multiple Sclerosis Walking Scale-12 (MSWS-12) has been a commonly used patient reported outcome for measuring walking impairment in research involving multiple sclerosis (MS). ObjectiveWe examined the possibility that cognitive processing speed (CPS) influences the association between MSWS-12 scores and other measures of ambulation (i.e., construct validity). Methods96 MS patients completed the MSWS-12, underwent a neurological examination for generating an Expanded Disability Status Scale (EDSS) score, and completed the Symbol Digit Modalities Test (SDMT), Timed 25-Foot Walk (T25FW), 4 trials on the GAITRite™ for generating the functional ambulatory profile (FAP) score, and Six-minute Walk (6MW). ResultsThe SDMT was significantly correlated with MSWS-12 scores (r=−.428) and T25FW (r=−.459), 6MW (r=.512), FAP (r=.275), and EDSS (r=−.404) scores. There were statistically significant correlations between MSWS-12 and T25FW (r=.568), 6MW (r=−.680), FAP (r=−.595), and EDSS (r=.737) scores. Lastly, four separate hierarchical linear regression analyses indicated that, after controlling for age, gender, disease duration, and clinical course, T25FW, 6MW, FAP, and EDSS scores individually were significant correlates of MSWS-12 scores, and the associations (i.e., standardized beta-coefficients) were still statistically significant with minimal attenuation when controlling for SDMT scores. ConclusionThere was minimal evidence that CPS influenced the construct validity of MSWS-12 scores.