Rapid Foot Tapping Ability Distinguishes between Multiple Sclerosis Sub-Types and Is Associated with Mobility Function

Background: Timed-up-and-go (TUG) and 25-foot walk test (25FWT) are common clinical measurements that require ambulation and are used to assess mobility in people with multiple sclerosis (MS). However, not all people with MS are ambulatory, and preliminary work from our laboratory (unpublished) suggests that while TUG and 25FWT can distinguish individuals with MS from non-MS controls (CON), they cannot distinguish between non-progressive (MS-NP) and progressive (MS-P) MS sub-types. Therefore, there is a critical need to identify a sensitive and non-ambulatory task that can distinguish MS sub-types.

Objectives: To determine whether rapid foot tapping ability can distinguish MS from controls and between the MS sub-types.

Methods: 30 participants with MS-NP, 30 participants with MS-P, and 17 age-and sex-matched controls participated in this study. Each wore inertial sensors (APDM, Inc., Portland, OR) on the foot that measured angular velocity and acceleration while tapping their foot as fast as possible for 10 s. Participants performed 3 trials on each foot while seated with self-selected knee and ankle angle. Sensor data was analyzed using a custom MATLAB program which identified taps as acceleration peaks that occurred after every other zero-crossing of angular velocity. TUG and 25FWT were administered to compare mobility to rapid foot tapping. ANOVA was used to analyze main effects of group followed by pairwise comparisons between groups.  Associations between foot tap count and mobility measures in MS groups were evaluated using Spearman’s rho. Significance was established as p<0.05. 95% confidence intervals for differences between means are reported.

Results: There was a main effect of group for foot tap count (p <0.001), such that tap count differed between CON and MS-NP (p=0.007, CI=[2.3, 13.7]) and MS-P (p<0.001, CI=[9.0, 18.4]); as well as between MS-NP and MS-P (p=0.040, CI=[0.3, 11.2]). Foot tap count was negatively correlated with both 25FWT (p=0.002, r_s=-0.459) and TUG (p=0.009, r_s=-0.403), indicating an association between the slowing of both tapping speed and mobility measures. 

Conclusions: Our results show that the number of rapid foot taps in 10 s differentiates between controls and MS, as well as among MS sub-types. In addition, the associations between foot tap speed and mobility measures such as the TUG and 25FWT suggest that rapid foot-tapping may be a useful marker for tracking or predicting progression of mobility dysfunction in people with MS, regardless of their ability to ambulate.