Effect of Fatigue on Sensory Impairment in Multiple Sclerosis

Background: Fatigue and sensory impairment are common findings in persons with Multiple Sclerosis (pwMS). MS fatigue is known to worsen with exertion, and previous studies have shown that both worsening fatigue and sensory loss can affect gait aswell as other mobility tasks. Anecdotally, MS patients have noted that symptoms of sensory impairment worsen with fatigue as well, but this has not been examined. 

Objectives: The purpose of this  study is to examine whether worsening MS fatigue affects  sensory impairment in pwMS. We hypothesize that as fatigue worsens in pwMS, sensation will also worsen. This may in part account for the worsening of gait and balance that is seen in pwMS as they become more fatigued. If our hypothesis is correct, it will suggest that sensation testing for persons with MS should be done in both a fatigued and unfatigued state.

Methods: A randomized crossover design was used. Ambulatory subjects with a definitive diagnosis of MS were recruited from local MS practices. Following obtaining consent and subject characteristics, subjects were randomized into walking (W) and resting (R) groups. All subjects received sensory testing using a biothesiometer on 6 key (B) lower extremity points. Subjects in the (W) group then performed a 6-minute walk (6MW) to induce fatigue, while subjects in the (R) group lay supine for 6 minutes to minimize fatigue. Fatigue was assessed using the Visual Analog Scale of Fatigue (VAS-F). Immediately following either 6-minute condition biothesiometer testing 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 mild to moderate MS disability and fatigue (mean EDSS=3.45, mean FSS 4.41), completed the study. Mean biothesiometer readings increased significantly  from pretest (x̅ =22.0 microns, SD=12.9) to posttest (x̅=25.6 microns, SD=13.7) in the (W)fatigued condition, p=. 001. There was no significant pre- to post- difference in sensation for the (R) unfatigued state. Subjects VAS-F scores increased significantly  following the  6-minute walk (x̄=33.8,SD=29.1,p=.0028).), and slightly decreased (x̄=-2.43,SD=9.6) during the 6 minute supine rest, indicating that subjects in the (W) condition were truly fatigued and those in the (R) condition were not.

Conclusions: Our results indicate that increasing fatigue in pwMS can result in worsening of sensation. This may in part explain the worsening of gait seen in fatigued MS patients. This finding may also explain the worsening of performance in other mobility tasks such as balance that have been shown to worsen with fatigue in pwMS. Clinically, our findings suggest that sensation testing in pwMS should be performed in both a fatigued and unfatgued state to get a more accurate picture of the extent of the effects of fatigue on sensory impairment.