LAUSR

BACKGROUND Rapid tapping tests have been shown to be reliable measures of upper motor neuron disease, and effectively examine motor function differences between multiple sclerosis (MS) and non-MS controls (CON), and between relapsing-remitting and progressive MS subtypes. To successfully perform rapid repetitive movements such as tapping, a person must be able to consistently turn on and off motor units to switch between the up and down movement phases. However, it is not clear which specific movement phase that occurs during tapping is different between MS subtypes. The objective of this study was to quantify and characterize performance differences during rapid hand- and foot-tapping tests between relapsing-remitting (RRMS) and progressive (PMS) forms of MS, as well as how both subtypes differ from non-MS controls. METHODS Participants in this study included 30 non-MS controls, 32 RRMS, and 31 PMS. Participants wore inertial sensors on all hands and feet and were instructed to tap as fast as possible for 10 s. Angular velocity from the gyroscope was used to quantify inter-tap interval (ms), coefficient of variation of inter-tap interval (COV), and up- and down-movement characteristics (duration (ms), COV, peak angular velocity (rad/s)). Differences between groups were examined with ANOVA and independent t-tests. Inter-tap interval was examined for its ability to distinguish between RRMS and PMS by a binary logistic regression analysis. Up-down movement characteristics were further evaluated for within-group directional differences (up- vs. down-phase movement components) with paired-sample t-tests. RESULTS Inter-tap interval for both hand- and foot-tapping differed between controls and MS, but only foot tapping was different between RRMS and PMS (RRMS = 286.7 ± 83.0 ms; PMS = 379.5 ± 170.9 ms; mean difference (d) = -92.8 ms). Logistic regression analysis showed foot-tap interval but not hand-tap interval has the potential to distinguish between RRMS and PMS (Area under the ROC = 0.71). Both up- and down-movement duration differences were consistent with the results for inter-tap interval, but up-movement duration showed larger mean group differences than down-movement differences. No significant group differences in overall inter-tap interval COV were detected for either hand- or foot-tapping; however, up-movement foot-tapping variation (CON = 18.7 ± 6.1; RRMS = 25.5 ± 11.2; PMS = 23.3 ± 8.6; CON vs RRMS d = -6.8; CON vs PMS d = -4.7), but not down-movement variation was different between controls and MS. Up- and down-peak angular velocity during foot-tapping were different between controls and PMS (CON Up = 1.4 ± 0.5 rad/s; PMS Up = 1.0 ± 0.4 rad/s; Up d = 0.4 rad/s; CON Down= 1.5 ± 0.6 rad/s; PMS Down = 1.2 ± 0.5 rad/s; Down d = 0.3 rad/s), and up-movement peak angular velocity differences showed larger mean group differences than the down-movement peak angular velocity between controls and PMS. CONCLUSION Foot-tapping differs between MS disease subtypes and has greater potential than hand-tapping to distinguish between subtypes. Performance in the up-movement showed larger group differences than the down-movement, suggesting that the anti-gravity up-movement during tapping may be more important diagnostically. Future studies should be conducted on the nature of the physiological mechanisms underlying impairments in anti-gravity movements in people with MS.