Postural control strategy during standing is altered in patients with multiple sclerosis

Disturbances in balance are one of the first reported symptoms of Multiple Sclerosis (MS), yet limited research has been performed to classify the postural control deficits in this population. This study investigated the variability present in the sway patterns during quiet standing in patients with MS (PwMS) and healthy controls. Subjects were assessed (eyes open, closed) standing on a force platform. Variability of the sway patterns was quantified using a measure of amount of variability (root mean square; RMS) and two measures of temporal structure of variability (Lyapunov Exponent - LyE; Approximate Entropy - ApEn). RMS results revealed significantly higher amount of variability in the sway patterns of PwMS. PwMS also exhibit increased regularity (decreased ApEn) and decreased divergence (decreased LyE) during standing compared to healthy controls. Removing vision resulted in significantly decreased divergence (decreased LyE) in the MS subject group. These changes in the temporal structure correspond well with the theoretical model of the optimal movement variability hypothesis and the results support using variability measures to understand the mechanisms that underline postural control in PwMS and possibly other neurodegenerative disease pathologies.