Local Dynamic Stability of Gait in People With Early Multiple Sclerosis and No-to-Mild Neurological Impairment

Poor dynamic balance, such as poor walking stability, is a hallmark of multiple sclerosis. Instrumental measures of local dynamic stability (LDS, e.g. short-term Lyapunov's exponents, sLyEs) are genuine measures of walking stability and increasingly used as dynamic balance indicators. The current work aims to investigate if people with multiple sclerosis (PWMS) with no clinical evidence of gait impairment suffer poor LDS of gait. Eighty PWMS with minimal impairment (EDSS <= 2.5) and twenty controls completed the Six-Minute Walk Test (6MWT) at their maximum speed, wearing inertial sensors. sLyEs were calculated from trunk vertical, mediolateral and anteroposterior (sLyE(AP)) acceleration. PWMS also completed a full clinical assessment including gait, balance and fatigue. Gait speed was lower in PWMS than controls (-15%), while sLyEs were larger in PWMS (+12%), even when adjusting for the different gait speed. High sLyE(AP) was associated with low gait speed, high impact of disease (including high fatigue) and poor balance, the three variables returned by a principal component analysis of the dataset of clinical measures. PWMS suffer poor LDS of gait, as indicated by large sLyEs. The association between high sLyE(AP) and poor balance supports the validity of sLyE(AP) as a dynamic balance measure. The inverse relationship between sLyE(AP) and gait speed is in line with the view that good balance is decisive for high gait speed. Finally, these findings are in line with the vicious circle linking poor balance and fatigue in PWMS, with fatigue worsening balance and poor balance leading to fatigue.