Examining the Influence of Processing Speed on the Relation between Backward Walking and Falls in Persons with Multiple Sclerosis

Background: Backward walking (BW) is a complex motor task that requires increased cognitive demands. In persons with multiple sclerosis (MS), our laboratory has demonstrated BW velocity as a marker of fall risk and cognitive correlate of information processing speed (IPS) and visuospatial memory. However, the extent to which the relation between BW and falls is dependent upon core cognitive function, like IPS and visuospatial memory is unknown.

Objectives: The objective of our study was to examine the discrete influences of IPS and visuospatial memory on the relation between BW and falls in persons with MS. Based on published preliminary data, we hypothesized that the relation between BW and number of falls is conditional upon IPS and visuospatial memory.

Methods: In a single session, spatiotemporal measures of forward and backward walking, IPS as measured by the symbol digit modalities test (SDMT), visuospatial memory as measured by the BVMT-R and self-reported retrospective fall history were collected. Using hierarchical regression modeling, moderation was tested in a second step including an interaction term predicting number of falls. Co-variates for all analyses included age and disease severity (Patient Determined Disease Steps [PDDS]).

Results: Thirty-eight individuals with relapsing-remitting MS were included in the moderation analyses. BW, IPS and co-variates significantly predicted the number of falls (R² = 0.301, p = 0.016), but IPS did not change the relation to BW (ΔR² = 0.013, p > 0.1). In a separate model, BW, visuospatial memory and co-variates also significantly predicted the number of falls (R² = 0.332, p = 0.008), but visuospatial memory did not change the relation to BW (ΔR² = 0.001, p > 0.1). The forward walking models generated comparable results.

Conclusions: There was no statistical evidence to suggest IPS or visuospatial memory as moderators of the relation between BW and falls in our small sample of individuals with MS. Larger scale studies examining additional cognitive domains impacted by MS (i.e., executive function and attention) are needed to establish a cognitive framework aimed at characterizing neurobiological processes relevant to BW and its clinical application in the assessment of fall risk.