Understanding how people with MS get tired while walking
Author(s): S. Piérard , R. Phan-Ba, M. Van Droogenbroeck
(Abstract release date: Sep 23, 2015) ECTRIMS Online Library. Piérard S. Oct 9, 2015; 116085
Background: Walking impairment is frequent, appears early in the disease course of MS patients (MSP), and is perceived as the most disabling symptom. When walking, patients get tired more and differently than healthy people (HP) [Phan-Ba et al PLOS 2012]. This limits their walking perimeter. Understanding this phenomenon is thus important to suggest adequate therapies at the right time.
Objective: Our aim is to understand how MSP get tired while walking compared to HP. Two groups of MSP are considered: those with a low disability level (MSPL) and those with a high one (MSPH). We consider two criteria to measure the disability: the EDSS and the deceleration index (DI) [Phan-Ba et al PLOS 2012]. The limit between the groups is set at DI=0.8 and EDSS=3 (inclusive for MSPL).
Methods: Many gait characteristics (GC) have been measured with the system GAIMS along a 500m path walked as fast as possible. The dataset gathers 464 visits of HP and 70 of MSP. Some people have been assessed several times. There are 33 visits in the group MSPL with the EDSS criterion, and 25 with the DI criterion. Statistical tests (Welch) were performed on the differences and relative differences of the GC measured during the first and last 100m of the test to detect differences between HP and MSPL, and between MSPL and MSPH, as in [ECTRIMS 2012 P755].
Results: Both criteria for defining the groups lead to similar conclusions. For many GC, the distributions of the variations are significantly different between MSPL and MSPH. The largest difference is for the relative difference of speed (p=0.000119 for EDSS and p=0.000021 for DI). In contrast, only the variation of the average lateral distance between the feet, which is related to the size of the base of support (and thus to the balance) shows a very significant difference between HP and MSPL (p=0.000116 for EDSS and p=0.000120 for DI). The balance does not seem to change much from MSPL to MSPH. Besides, we note that the variance decreases slightly from HP to MSPL and increases a lot from MSPL to MSPH.
Conclusions: Statistically, from the motor fatigue point of view, it seems that the course of the MS disease is divided in two different stages. In the first one, MSP get more tired than HP because of a deterioration of the balance. Then, in the second one, their fatigue becomes related to a faster decrease of the walking speed. This suggests that physical therapy exercises focused on the balance could be given to MSP in the early stage of the disease.
Disclosure: The authors have nothing to disclose. We thank the Walloon region of Belgium for partly funding the project GAIMS.
I am not saying that this work provides us with the definitive answer on the mechanics of fatigue in MS, however, it does provide an interesting angle which should be explored further.
The authors studied the walking characteristics along a 500m walked as fast as possible between controls, MSers with a low disability levels, and MSers with a high disability level. They argue that MSers get more tired more and differently from healthy people, and use the assessment to determine what characteristics in the walking lead to this.
They found a difference on how MSers get tired whilst walking can be used to divide the MS disease into two stages. In stage 1 (EDSS <3; moderate disability but still fully ambulatory) MSers got more tired than those without MS purely due to a deterioration in balance. In stage 2 (EDSS <4; able to walk without aid for 500m) the fatigue is related to a faster decrease in walking speed. The later finding is obvious, we already know/suspected that the reduction in walking ability is the largest contributor to fatigue in MSers who have walking difficulties. What we didn’t know was that poor balance does the same thing in early MS in those without clear indicators of a problem with walking.
Therefore, at least in the early MS, interventions focused on improving balance may be a treatment option for improving fatigue levels.