Physical function across the lifespan in adults with multiple sclerosis: An application of the Short Physical...

Multiple sclerosis (MS) typically has its onset in early and middle adulthood, but the population is steadily becoming more dominated by older adults. One of the primary consequences of both MS and aging involves declines of lower extremity physical function and mobility. This cross-sectional study compared physical function status based on Short Physical Performance Battery (SPPB) summary and component scores between persons with MS and healthy controls across 6 age groups. We further examined associations between SPPB summary scores and component scores as well as associations between summary scores and measures of physical and cognitive function for identifying the strongest correlates of SPPB summary scores.

The study involved secondary analysis of cross-sectional data from multiple studies. Ambulatory adults with MS who were relapse-free for the last 30 days were recruited, and controls were recruited based on similar criteria to adults with MS except without the diagnosis of MS or relapses. The sample of 345 persons with MS and 174 controls completed questionnaires regarding demographic and clinical information and underwent assessments of physical and cognitive function including the SPPB, 6-Minute Walk, Timed 25-Foot Walk, Symbol Digit Modalities Test, California Verbal Learning Test-Second Edition, and Brief Visuospatial Memory Test-Revised.

The two-way ANOVA indicated a main effect of MS status (F(5,500)=34.74, p<.01, η²=0.065), a main effect of age (F(1,500)=3.88, p<.01, η²=0.037), and no MS status by age interaction (F(5,500)=1.20, p=.31, η²=0.012) on SPPB scores. The bivariate correlation analysis indicated that summary SPPB scores were associated with component SPPB scores in the overall samples of persons with MS (r_s=0.71 to 0.83) and controls (r_s=0.42 to 0.91) as well as within most age groups of MS (r_s=0.63 to 0.91) and controls (r_s=0.34 to 1.00). The associations between SPPB scores and physical function outcomes were larger in the sample of persons with MS (r_s=-0.72 to 0.76) than controls (r_s=-0.47 to 0.48). SPPB scores were further significantly associated with scores on cognitive outcomes in persons with MS (r_s=0.31 to 0.43), whereas these associations were weaker in controls (r_s=0.09 to 0.32). Overall, the associations between SPPB scores and physical function outcomes were stronger than the associations between SPPB scores and cognitive function outcomes.

Overall, MS status and aging have additive effects on physical function, and the summary SPPB score may be driven by a specific component within each age group. SPPB scores may be driven more by mobility rather than cognition, and are consistent with cognitive-motor coupling in MS. The novelty of this study provides evidence of worsening physical function based on the application of the SPPB and its scores across the lifespan in persons with MS and controls, and this has important implications particularly given the increasing prevalence of older adults with MS.