A comparison of upper limb function in subjects with multiple sclerosis and healthy controls using an inertial measurement unit

Upper limbs (UL) dysfunction is frequent in people with Multiple Sclerosis (PwMS). Several objective measures of UL function are proposed; however, their use is mostly confined to assess subjects with mild-to-moderate disability and requires fine motor skills, often impaired in high disability level subjects. Thus, a tool to score UL function in the advanced disease stage is lacking. The aim of the study is to analyse and compare UL unilateral and bilateral movements of healthy control (HC) and PwMS, at different disability levels, using an instrumented version (Inertial Measurement Unit, IMU) of the 15-seconds finger-to-nose test (FNT). Each movement cycle was segmented in going/adjusting/returning phases. The inter-hand interval (IHI) allowed assessing bilateral coordination (i.e. synchrony) in each phase. The larger IHI, the more severe the bilateral coordination impairment is. After stratifying PwMS for disability level (PwMSLOW, Expanded Disability Status Scale, EDSS <= 5.5 and PwMSHIGH, EDSS >= 6), the ANOVA on IHI showed significant differences between PwMS and HC (p<0.001) in all phases. However, only the going phase IHI showed significantly higher asynchrony in PwMSHIGH than PwMSLOW and HC (p<0.001) and no differences between PwMSLOW and HC. The going phase IHI seems to be a clinical marker specific for high disability level PwMS. These findings suggest inertial sensors during FNT could be an easy-to-use method for a more detailed quantitative characterization of UL function in PwMS also in subjects with EDSS greater than 6.