Therapeutic effects of anti-spastic medication on neuromuscular abnormalities in SCI: a system identification approach

Facilitatory effects of anti-spastic medication on robotic locomotor training in people with chronic incomplete spinal cord injury

Background

The objective of this study was to investigate whether an anti-spasticity medication can facilitate the effects of robotic locomotor treadmill training (LTT) to improve gait function in people with incomplete spinal cord injury (SCI).

Methods

Individuals with chronic incomplete SCI were recruited and carried out a 4 week intervention of either locomotor treadmill training (LTT) alone (n = 26) or LTT combined with Tizanidine (TizLTT), an anti-spasticity medication (n = 22). Gait function was evaluated using clinical outcome measures of gait, speed and endurance. To better understand the underlying mechanisms of the therapeutic effects, maximal strength, active range of motion (AROM) and peak velocity (Vp) of ankle dorsi- and planter-flexor muscles were also measured. Differences were assessed using two-way mixed design analysis of variance. The number of subjects that achieved the minimal important difference (MID) for clinical scores was also measured for each group, and the results of those that did attain the MID were compared with those that did not.

Results

Both LTT and TizLTT resulted in significant improvements in walking speed and dorsiflexion maximum strength, with no significant differences between them, using group-averaging analysis. However, using the MID analysis, a higher proportion of subjects in the TizLTT group achieved the MID for walking speed (40%) compared with LTT alone (13%). Those that achieved the MID for walking speed were significantly higher functioning at baseline than those that did not in the TizLTT group, and the change in walking speed was associated with the change in dorsiflexion peak velocity (R² = 0.40; P < 0.05).

Conclusion

Tizanidine appears to facilitate the effects of LTT on gait function in individuals with chronic SCI that are higher functioning at baseline. We speculate that this may be due to restoration of inhibitory mechanisms by Tizanidine, resulting in greater stretch in the planterflexor muscles during the LTT.

Comparison between the therapeutic effects of robotic-assisted locomotor training and an anti-spastic medication on spasticity

We studied the effects of robotic-assisted locomotor (LOKOMAT) training or an anti-spastic medication (tizanidine) on neuromuscular abnormality associated with spasticity in persons with incomplete Spinal Cord Injury (SCI). Subjects were randomly divided to three groups: Lok, Tiz, and Cont. LOKOMAT training was performed 3 days/week for 4 weeks, with up to 45 minutes of training per session. Tizanidine (2mg) was administered (4\day), for 4 weeks. Subjects in Cont group received no intervention. The participants were evaluated before and after 4 weeks of training, and the effects of training on the intrinsic (muscular) and reflexive components of the neuromuscular properties were quantified over the ankle range-of-motion. A parallel-cascade system identification technique was used to determine the reflex and intrinsic stiffness of the ankle joint as a function of ankle position at each time point. The intercept and slope of the stiffness vs. joint angle curve were then calculated and tracked over the four-week period. The number of subjects that achieved the minimally important difference (MID) for the intercepts and slopes, and levels of changes were compared. Both Lokomat and tizanidine resulted in significant reduction in both intercept and slope of reflex and intrinsic stiffness. However, a higher proportion of subjects in Lok group achieved the MID for the reflex (>90%) and intrinsic (65-78%) parameters compared with Tiz group (up to 63% and 25% for reflex and intrinsic parameters, respectively). The levels of reduction were also higher in the Lok than the Tiz group. No one in the Cont group achieved the MID. Our findings demonstrate that LOKOMAT training can be more efficient in modifying neuromuscular abnormalities associated with spasticity than tizanidine.