Construct Validity of the Four Square Step Test in Multiple Sclerosis

Objective To expand the construct validity of the Four Square Step Test (FSST) in people with multiple sclerosis (PWMS). Design Cross-sectional study. Setting Multiple sclerosis center. Participants PWMS (N=218; 133 women, 85 men; mean age, 43.2±13.5y; mean disease duration, 7.5±7.7y since diagnosis) were enrolled in the study. The Expanded Disability Status Scale score was 3.1±1.3, indicating minimal to moderate neurologic disability. Interventions Not applicable. Main Outcome Measures The FSST, posturography measures, 2-minute walk test, timed Up & Go test, timed 25-foot walk, fall status, Falls Efficacy Scale International, Modified Fatigue Impact Scale, instrumented cognitive assessment, and 12-item Multiple Sclerosis Walking Scale. Results The FSST score of the total sample was 11.0±4.9. Significant differences were observed between the very mild, mild, and moderate disability groups: 8.8±3.4, 11.1±4.9, and 14.1±5.3, respectively. In terms of fall status, the fallers demonstrated a significant slower FSST score than the nonfallers (12.5±5.7 vs 9.0±2.6, respectively). Modest significant correlation scores were found between the FSST and the timed Up & Go test and 2-minute walk test (Pearson ρ=.652 and ρ=−.575, respectively). In terms of posturography, all measures were significantly associated with the FSST scores. A significant positive relation was observed with the visual spatial cognitive domain (Pearson ρ=−.207). Conclusions The current study supports and broadens the construct validity of the FSST in PWMS.