Exploring the Benefits of FES on Gait for Patients with Multiple Sclerosis

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By Phil Stevens, MEd, CPO, FAAOP

Today's functional electrical stimulation (FES) devices for the management of foot drop include single-channel, surface-electrode systems such as the Innovative Neurotronics WalkAide, the Odstock Dropped Foot Stimulator (ODFS), and the Bioness NESS L300. There is quite a bit of available research on the use of FES systems, the majority of which is focused on its use in the management of patients following cerebral vascular accident (CVA) and its effect on gait.1 Clinical experience, however, suggests that patients with multiple sclerosis (MS)-related foot drop are more likely to research solutions and pursue this technology. While CVA-based literature provides some insights into the possible benefits of FES, there are important differences between patients attempting to recover from a non-progressive CVA and patients confronting the progressive declines associated with MS. Fortunately, there are several studies that provide insights on the effects of FES in the MS population, particularly on those patients who have been diagnosed with the more aggressive secondary progressive form of the disease. The observations made in those clinical trials can help practitioners to have more productive conversations with current and prospective FES patients who have MS.

Early Observations

A 2008 study by Paul et al. details the experience of 12 patients with secondary progressive MS as they completed a five-minute walk test (5MWT) around an elliptical track with and without their ODFS FES intervention.2 With the FES intervention, the authors reported a 15 percent average improvement in walking velocity and a 12 percent decrease in physiological cost.2 While these results are impressive, a couple of important variables must be taken into account. First, the study subjects had been using FES for an average of three-and-a-half years at the time of the evaluation; the subjects' experience ranged from seven months to almost six years. Thus, for this cohort, rather than describing the increase in walking velocity with FES, it might be more accurate to point out the 12 percent decrease in walking velocity that occurred in the absence of FES since the use of the ODFS was their baseline experience. Second, the effects of FES on walking velocity were quite variable. While no subjects walked faster without the FES, the improvements in walking velocity with the ODFS ranged from 0-44 percent. This is consistent with the clinically observed variability in MS presentations and underscores the frustrating reality that what works for some patients may not work as well for others.

Despite these limitations, the observed improvements in velocity are consistent with another study published in 1999 in which 21 patients with MS experienced a 14 percent improvement in walking velocity following 18 weeks of FES use.3 Taken together, these trials serve as a starting point for documenting the potential benefits of FES among this patient population.

Dissecting the Effects

An additional limitation of the 2008 study is that it only reports on a moment in time, rather than on the changes that occur as patients transition into the device and how these changes might compare with those seen in the natural history of this population. Given the progressive nature of MS, the effectiveness of FES over time becomes an important consideration. These considerations were taken into account in a 2009 randomized controlled trial in which a cohort of 20 patients with secondary progressive MS was assigned to the FES intervention, and a second, comparable cohort was assigned to a home exercise program. Both groups were followed for several weeks.4 In an attempt to assess the effect of FES on both short-distance walking velocity and walking endurance, the authors reported the performance values on both the ten-meter and three-minute walk tests. Repeated evaluations of the FES group with and without use of the FES device during the assessment help describe the individual orthotic and therapeutic effects associated with this modality in this population. The orthotic effect is that which is immediately attributable to the stimulation at the time of testing. The therapeutic effect is that which is observed over time when patients are using the FES intervention but are tested without it. The combined effects are those seen over time with the use of FES at the time of assessment.

In this clinical trial, the average immediate orthotic effect on walking endurance was not measured, as the authors only conducted a single baseline assessment and this was without stimulation. However, the beneficial effects of FES became apparent with time. A therapeutic effect on walking endurance was seen in the threeminute walk performances in the FES cohort without stimulation. Mean scores increased by 13 percent, from 99 meters to 112 meters, between the initial assessment and a six-week follow-up.4 This effect was maintained at 12- and 18-week follow-ups. A comparable therapeutic effect was also seen in the control group that underwent a home exercise program. A combined effect was seen in the FES group when the tests were performed with stimulation. In this condition, researchers observed a mean increase of 23 percent at the sixweek follow-up relative to the no stimulation baseline condition. This combined effect improved to 26 percent by the 18-week follow- up (Table 1).4

Table 1: Mean three-minute walk test performance in meters for the control group (home exercise program) and FES group with and without stimulation. Adapted from Barret et al., 2009.4

In contrast to the effects on walking endurance, the effects of FES on short-distance walking speeds were fairly nominal. With the exception of a single outlier condition observed at week 18 in the FES without stimulation group, short-distance walking speeds stayed within 5 percent of the baseline assessment.4

Activities of Daily Living

A later paper written by the same research team as the 2009 study, and presumably reporting on many of the same patients, went beyond the observations of walking speed and endurance, looking at the effects of FES on activities of daily living (ADL) and fall rates. The authors used the Canadian Occupational Performance Measure (COPM) to assess the effects of the ODFS.5

The COPM is an individualized outcome measure in which subjects ultimately define the tasks on which they will be rated as well as their performance on and satisfaction with their ability to accomplish those tasks. In a semi-structured interview, subjects identify their individual performance challenges encountered during a typical day. The subject then rates the importance of each activity, and the top five activities are selected for further evaluation. The subjects then rate their ability to perform each activity on a scale from one to ten, and their satisfaction with their performance on a one to ten scale, with higher scores indicating greater levels of ability and satisfaction.

Fifty-three subjects were followed in this trial. The subjects identified 265 different activities, the vast majority of which were related to walking and mobility. The most commonly cited performance challenges are listed in Table 2.

Table 2: Daily performance challenges identified by subjects with secondary progressive multiple sclerosis using the COPM and the relative prevalence with which they were identified. Adapted from Esnouf et al., 2010.5

As with the previous study, subjects were randomly assigned to either an FES cohort or a home exercise cohort. Following 18 weeks in their respective cohort, subjects reevaluated their performance and satisfaction scores on the top five activities that they had earlier identified using the COPM. Several differences were observed between the two cohorts. The home exercise cohort perceived a level of improvement at the conclusion of the trial. These subjects showed an increased score of two points or more in both performance and satisfaction on 17 percent of the problems they had identified.5 The median score for these activities increased by three points in performance and four points in satisfaction. The FES contingent perceived an even more striking level of improvement. In this cohort, subjects reported an increased score of two points or more, with median improvements in these scores reported at four points for performance and five points for satisfaction on 35 percent of the COPM activities they had initially identified. In short, relative to their peers assigned to the home exercise cohort, the FES group experienced greater improvement in their perceived ability to perform those challenging ADLs that were most important to them.

The greatest improvements in satisfaction scores for both cohorts were observed in the task of being unable to walk a distance due to fatigue. These ratings improved by an average of three points for subjects in the home exercise group who emphasized this task. For subjects in the FES group who identified this task, satisfaction ratings improved by an average of five-and-a-half points. Interestingly, the elevated satisfaction scores were accompanied by fairly nominal mean improvements in perceived performance scores.5

Tripping was the most commonly reported problem. Members of the FES group who identified tripping as one of their five most important ADL challenges reported a median improvement of three-and-a-half performance points and four-and-ahalf satisfaction points for that task. In contrast, members of the home exercise group who identified tripping as one of their five most important ADL challenges reported a median response of no change in both performance and satisfaction for this task.5

These observations are consistent with the second component of this trial in which study subjects kept a fall journal for the 18-week observation period. The median number of reported falls in the FES group was five. By contrast, the median number of falls experienced by the home exercise cohort was 18.5 Hence, the use of FES was associated with comparatively reduced fall rates over the 18-week trial.

These collective findings are consistent with conference proceedings published in 2004 in which 285 FES users (43 of whom had MS) were asked to select from a list of 14 possible reasons why they chose to use the device.6

The most commonly cited reasons included the following:

  • Reduced effort while walking (88 percent)
  • Reduced risk of tripping (88 percent)
  • Increased confidence while walking (78 percent)
  • Increased walking distance (75 percent)

Longer-Term Effects

The last study differs from the previously mentioned studies in that it followed two broad categories of patients after their introduction to the WalkAide FES: a "nonprogressive" cohort made up predominantly of patients with CVA, and a "progressive" cohort made up almost exclusively of patients with secondary progressive MS. In addition to comparisons between the two groups, subjects were followed for a longer period of time, with the final assessments reported at 11 months post intervention.7

Drawing upon these observations, the authors concluded that the increases in walking speed observed after three months of FES use were similar for both groups at roughly 15-20 percent improvement in both short- and longer-distance walking events. At three months, the authors began to see a divergence. While the nonprogressive group continued to experience gains in gait speed both with and without stimulation (orthotic and therapeutic effects), the patients with MS experienced a plateau in walking speed and endurance at about three months, followed by a slight decline in performance at the remaining assessments.7 The authors suggest that this decline in endurance and speed is likely a result of the progressive nature of MS along with possible weakening of other muscle groups outside of the dorsiflexors that were not being stimulated during the trial. In short, for patients with MS, the therapeutic effects achieved through the use of FES appear to be eroded to some extent by the progressive nature of the disease.7

Summary

As with other populations who use FES for the management of foot drop, appropriately selected patients with MS also experience increased walking speeds with FES use. These improvements are more readily observed in sustained walking activities than in short-distance trials. Furthermore, these improvements in walking speed appear to be a combination of immediate orthotic effects and longer-term therapeutic effects. However, unlike their peers with nonprogressive disorders such as CVA, patients with MS are dealing with a progressive disease process that appears to offset some of the gains in endurance and velocity. Importantly, many of the benefits of FES in this population appear to be experienced outside of level-ground walking, with preliminary evidence suggesting that the intervention may assist with the performance of many important ADLs, with reduced tripping and fall rates being the most striking observations in this domain. An awareness of these findings will help clinicians guide the expectations of current and potential FES users who have MS.

Phil Stevens, MEd, CPO, FAAOP, is in clinical practice with Hanger Clinic, Salt Lake City, Utah. He can be reached at

References

  1. Stevens, P. M., and R. B. Hunsaker. 2010. Recent findings regarding the efficacy of functional electrical stimulation in patients with chronic hemiplegia and multiple sclerosis: A narrative literature review. Journal of Prosthetics and Orthotics 22(3):166-71.
  2. Paul, L., D. Rafferty, S. Young, L. Miller, P. Mattison, and A. McFadyen. 2008. The effect of functional electrical stimulation on the physiological cost of gait in people with multiple sclerosis. Multiple Sclerosis Journal 14(7):954-61.
  3. Taylor, P. N., J. H. Burridge, A. L. Dunkerley, D. E. Wood, J. A. Norton, C. Singleton, and I. D. Swain. 1999. Clinical use of the Odstock dropped foot stimulator: Its effect on the speed and effort of walking. Archives of Physical Medicine and Rehabilitation 80(12):1577-83.
  4. Barrett, C. L., G. E. Mann, P. N. Taylor, and P. Strike. 2009. A randomized trial to investigate the effects of functional electrical stimulation and therapeutic exercise on walking performance for people with multiple sclerosis. Multiple Sclerosis Journal 15(4):493-504.
  5. Esnouf, J. E., P. N. Taylor, G. E. Mann, and C. L. Barrett. 2010. Impact on activities of daily living using a functional electrical stimulation device to improve dropped foot in people with multiple sclerosis, measured by the Canadian Occupational Performance Measure. Multiple Sclerosis Journal 16(9):1141-7.
  6. Taylor, P. N., M. Johnson, G. E. Mann, I. D. Swain. 2004. Patterns of use and users' perceptions of the Odstock Dropped Foot Stimulator following stroke and multiple sclerosis. 9th Annual Conference of the International FES Society and 2nd FESnet Conference, Bournemoth, United Kingdom, (ISBN 1-85899-191-9) 296-8.
  7. Stein, R.B., D. G. Everaert, A. K. Thompson, S. L. Chong, M. Whittaker, J. Robertson, and G. Kuether. 2010. Long-term therapeutic and orthotic effects of a foot drop stimulator on walking performance in progressive and nonprogressive neurological disorders. Neurorehabilitation & Neural Repair 24(2):152-67.