Effect of Spasticity on Fatigue in Multiple Sclerosis

Background: Fatigue is one of the most common findings in persons with Multiple Sclerosis (pwMS). It has been shown to worsen with exertion over time, and can significantly impact mobility. The specific manner and mechanisms by which fatigue impacts mobility tasks such as gait and balance are not known. There is some evidence that specific MS impairments are worsened by fatigue and that this may account for worsening  mobility in pwMS as fatigue increases.Spasticity is a common MS impairment that can impact gait, but there is only anectdotal evicence that it worsens with fatigue.

Objectives: The purpose of this study is to examine the effects of fatigue on spasticity in pwMS. We hypothesize that as fatigue increases, spasticity will also increase in pwMS. If our hypothesis is correct, it will suggest that part of the fatigue related worsening of MS gait seen in MS is due to worsening of spasticity ,and that therefore treatment of one may result in effects on the other.

Methods: A randomized controlled crossover design was used. Ambulatory subjects with a definitive diagnosis of MS were recruited from local MS practices. Following obtaining informed consent and subject characteristics, subjects were randomized into walking (W) and resting (R) groups. Spasticity was tested using the Modified Ashworth Scale (MAS) and the impact of spasticty was measured using the Multiple Sclerosis Spastiity Scale-88 (MSSS-88). The overall impact of fatigue was measured using the Fatigue Severity Scale. (FSS). After spasticity testing the (W) group performed a 6-minute walk  (6MW) to induce fatigue while the (R) group lay supine for 6 minutes to minimize fatigue. The fatiguing effects of the 6-minute walk was measured using the Visual Analog Scale of Faitgue (VAS-F). Immediately following either 6-minute condition the MAS was repeated. This was repeated for three trials in one week, followed by a 2-week detraining period. Subjects then crossed over, performing whatever type of testing they did not participate in initially.

Results:  17 subjects with MS (EDSS=3.45) and with self-identified impact of spasticity(MSSS-88=160.7), and fatigue (FSS=4.41) completed the study. In the fatigued condition, MAS scores decreased non-significantly from pretest (x̅ .84, SD=. 48) to posttest (x̅ = .76, SD=. 47), p= .07.In the unfatigued condition, MAS scores also decreased non-significantly from pretest (x̅ = .79, SD=.53) to posttest (x̅ = .73, SD=.45), p=.185. VAS-F scores indicated that subjects found the walking condition  significantly more fatiguing than the resting condition (p=.0028).

Conclusions:  Results in this study do not show an increase in spasticity due to fatigue. This is in contrast to the findings that other MS symptoms do increase with fatigue.The finding in this study suggest that the worsening of gait due to fatigue in pwMS are due to factors other than spasticity.This may however reflect limitations with the spasticity testing method.