Reliability, Validity, and Responsiveness of the Patient-Specific Functional Scale for Measuring Mobility-Related Goals in People With Multiple Sclerosis

Abstract

Background and purpose: This study's purpose was to investigate the reliability, validity, and responsiveness of the Patient-Specific Functional Scale (PSFS) for measuring mobility-related goals in people with multiple sclerosis (MS).

Methods: Data from 32 participants with MS who underwent 8 to 10 weeks of rehabilitation were analyzed (Expanded Disability Status Scale scores 1.0-7.0). For the PSFS, participants identified 3 mobility-related areas where they had difficulty and rated them at baseline, 10 to 14 days later (before starting intervention), and immediately after intervention. Test-retest reliability and response stability of the PSFS were calculated using the intraclass correlation coefficient (ICC 2,1 ) and minimal detectable change (MDC 95 ), respectively. Concurrent validity of the PSFS was determined with the 12-item Multiple Sclerosis Walking Scale (MSWS-12) and the Timed 25-Foot Walk Test (T25FW). PSFS responsiveness was determined using Cohen's d , and minimal clinically important difference (MCID) was calculated based on patient-reported improvements on a Global Rating of Change (GRoC) scale.

Results: The PSFS total score demonstrated moderate reliability (ICC 2,1 = 0.70, 95% CI: 0.46 to 0.84) and the MDC was 2.1 points. At baseline, the PSFS was fairly and significantly correlated with the MSWS-12 ( r = -0.46, P = 0.008) but not with the T25FW. Changes in the PSFS were moderately and significantly correlated with the GRoC scale (ρ = 0.63, P < 0.001), but not with MSWS-12 or T25FW changes. The PSFS was responsive ( d = 1.7), and the MCID was 2.5 points or more to identify patient-perceived improvements based on the GRoC scale (sensitivity = 0.85, specificity = 0.76).

Discussion and conclusions: This study supports the use of the PSFS as an outcome measure in people with MS to assess mobility-related goals.Video Abstract available for more insights from the authors (see the Video, Supplemental Digital Content 1, available at: http://links.lww.com/JNPT/A423 ).

Trial registration: ClinicalTrials.gov NCT04633759 NCT04548154.