The Six-Spot Step Test Versus the EDSS: Measuring Ability Rather Than Disability in People With MS

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By Phil Stevens, MEd, CPO, FAAOP
foot with AFO

I've noticed a rather discouraging trend in the lower-limb orthotic management of patients with multiple sclerosis (MS). While exceptions abound, it's frustrating to observe that many of the individuals who come in with a diagnosis of MS probably should have been in to see me or one of my colleagues five to ten years earlier. By the time they get to an orthotist, they often report having dealt with gait challenges for years that could have been reasonably managed much sooner. I've often wondered why the MS medical community doesn't get these folks to us sooner so we can enable improved safety and function in a more timely manner.

The reasons are likely multifactorial. They probably include the gradual onset of MS-related disability, the continued emphasis on pharmaceutical treatment options, and that treating physicians frequently have backgrounds in neurology rather than physical medicine. However, another aspect that is almost certainly working against earlier orthotic management in this population is its gold standard of assessment and classification, the Expanded Disability Status Scale (EDSS). This grading paradigm categorizes lower-limb orthoses, along with crutches and walkers, as markers of disability rather than enablers of increased ability and societal engagement.

When orthosis use is tied directly to the assignment of an increased level of disability, it's not surprising that treating physicians tend to be slower to prescribe them as a treatment option-within the structure of the EDSS, doing so acknowledges progression of the patient's disability that the physician is trying to forestall.

In any battle, a wise army seeks and claims the high ground. In the orthotic management of MS, as long as our interventions are seen as markers of disability, we hold the low ground. This article introduces the fundamental limitations of the EDSS and suggests other outcome measures that could be used to claim higher ground, allowing the profession to demonstrate the patient's improved physical performance with orthosis usage.

EDSS

hand gripping crutch

The EDSS was originally described by John F. Kurtzke, MD, in 1983.1 It is a non-continuous scale that ranges from 0 (normal neurologic exam) to 10 (death due to MS). Its completion is a rather tedious affair to all but trained neurologists, relying in large part upon an individual's Functional Systems Scores (FSS). These are graded ratings of the patient's visual, brain stem, pyramidal, cerebellar, sensory, bladder, and mental functional systems that are beyond the scope and intent of this article. Importantly, grades 0-4.5 are described as "fully ambulatory," defined by differences in an individual's FSS. However, in practice, ambulatory differences appear to be present even in these lower EDSS scores.

Beginning at 4.5, the EDSS begins to more fully consider mobility.1 The portions of those descriptions pertaining to mobility are as follows:

4.5: Fully ambulatory without aid, up and about much of the day, able to work a full day...able to walk without aid or rest for [about] 300 meters

5.0: Ambulatory without aid or rest for about 200 meters; disability severe enough to impair full daily activities (e.g., to work a full day without special provisions)

5.5: Ambulatory without aid or rest for about 100 meters; disability severe enough to preclude full daily activities

6.0: Intermittent or unilateral constant assistance (cane, crutch, brace) required to walk about 100 meters with or without resting

6.5: Constant bilateral assistance (canes, crutches, braces) required to walk about 20 meters without resting

7.0: Unable to walk [more than] approximately 5 meters even with aid, essentially restricted to wheelchair; wheels self in standard wheelchair and transfers alone; up and about in wheelchair some 12 hours a day




The narratives of higher levels of disability within the EDSS are beyond the scope of this article but include increased dependence within a wheelchair, a compromised ability to communicate, and becoming bedridden.

In reviewing the associated narratives of the EDSS, there are several factors that may be problematic for the orthotic community to absorb within its usual intervention protocols. First of all, it's challenging to discern where most of our patients might fit into this structure. If a patient who benefits from an orthosis is able to compensate for his or her gait deficits without a device to walk 200 meters, does the patient reach the status of a 5.0? If so, why would the test require him or her to do so? How does the classification system treat someone who is ambulatory throughout the day with the benefit of one or two AFOs? A patient like this certainly ambulates more than 100 or 200 meters, or in some cases even more than 300 meters, but does brace usage categorize him or her at the same level as someone who struggles to walk 20 meters? Can an active patient's EDSS rating jump from 5.0 to 6.0 simply because he or she chooses to use an AFO for foot drop?

hand gripping crutch

The EDSS is the benchmark for classifying disability in the MS population, and covers the broadest conceivable range of function, but it doesn't appear to be sensitive enough to distinguish nuanced performance among patients who may visit an orthotist. Frustratingly, the application of an orthosis to enable greater functional mobility would actually result in greater disability on the EDSS. In short, the rating system fails to appreciate any functional benefits associated with the use of an AFO.

What Matters Most?

A series of articles published earlier this year explores other ways to measure and characterize functional mobility more discretely than the EDSS and without defined penalization for the use of a lower-limb orthosis. Stellmann et al. studied the ecological validity of three standards of walking tests: the ten-meter walk test (10MWT), the two-minute walk test (2MWT), and the six-minute walk test (6MWT).2 They did so by having 28 patients with MS perform each test, and then having the patients wear an accelerometer for seven days to determine a) how often do the patients ambulate the distance they demonstrated in the initial test or for those amounts of time on a daily basis, and b) when they do so, are they moving at their test speeds.

The answers were, unsurprisingly, a) not very often, and b) not really. The subjects presented with a median EDSS score of 3.2 with 50 percent of them scoring between 2.5 and 4.1. Thus, by definition, these subjects were largely seen as fully ambulatory. However, they only walked for six uninterrupted minutes an average of once every three days. Before we get too critical, ask yourself and answer honestly, how often do you walk for six uninterrupted minutes? Designed as a stress test for heart patients, it's not too surprising to observe a reluctance to engage in an unsolicited 6MWT with great regularity.

However, the cohort was an active one, covering, on average, over 4,000 meters per day and taking well over 5,500 steps. They just did so in short bursts. Two minutes of uninterrupted walking was observed with greater frequency, approaching, on average, three instances per day, and 30 seconds of uninterrupted walking approached a dozen occurrences per day.

silhouette of man with crutches over his head

The speeds selected for daily ambulation were much slower than those demonstrated in the clinical tests, but this appears to be a product of the tests themselves. Short distance walking tests are often conducted at either self-selected or fast walking speeds. In Stellman et al.'s work, the instructions given to the patients were to walk "at fastest but safe speed."2 There is, therefore, little wonder that for uninterrupted walking sequences of at least 50 steps, the average recorded walking speed was about 20 percent slower than that measured during a 10MWT. Again, ask yourself and be honest, how often do you walk at your fastest possible speed?

The take-home messages from Stellman et al.'s work are twofold. First, if you want to test endurance, the 2MWT appears to be more representative of the sustained walking events the population with MS will experience. Second, having patients walk at self-selected walking speeds is likely more ecologically valid than having them walk as fast as possible. However, this latter point becomes less relevant among individuals with greater disability as the differences between their self-selected and fast walking speeds become less and less.

What Trends Should Be Watched For?

The next article under consideration is the work of Preiningerova et al., wherein they asked 284 patients with MS to walk across a GAITRite mat at both their self-selected and fast-as- possible gait speeds. The cohort spanned the gamut of ambulatory patients within the EDSS (0-6.5) with reasonable sample sizes at all levels. The researchers observed a number of insightful trends. First, even though EDSS scores from 1.0-4.5 are described as "fully ambulatory," average gait speeds decreased with increasing levels of disability across the spectrum of EDSS scores (Table 1).

Table 1
leg with AFO

As discussed earlier, the ability of patients with MS to increase their gait speeds from their self-selected walking speeds declines with increasing disability (Table 1). Other patterns of decline were also evident. Step length, for example, decreased with each higher range of EDSS scores, beginning with mild EDSS scores and continuing until it plateaued at EDSS level 6.0. Time spent in double support also increased with higher levels of disability, with the increases reaching statistical significance at EDSS scores from 3.0-3.5 and continuing to increase until EDSS score 6.5. Thus, a progressive pattern of decline is seen even at minimal and modest levels of disability as velocity slows, step length decreases, and the time spent in double support increases.2 This data suggests that ambulatory compromises begin sooner than the EDSS is able to appreciate them. If successful rehabilitation of MS is viewed in terms of restoring gait speed and step length, lower-limb orthoses are more likely to be viewed as an assistive modality than a marker of progressive disability.

Is There a Better Standard?

Summarizing to this point, the EDSS represents a broad classification approach that fails to capture nuanced gait changes associated with MS. Straight-line timed walking tests like the 10MWT and 2MWT appear to be more sensitive to MS-related disability but have been criticized due to their apparent lack of ecological validity. Is there a better standard that could be used to assess gait function in patients with MS that is sensitive to differences in presentation but better captures the day-to-day challenges experienced by patients?

One candidate for such a test can be found in the Six-Spot Step Test (SSST), described in Figure 1.4-5 It has demonstrated strong correlation with both the 25-foot walk test (25FWT) and the EDSS and has good test-retest reliability.4 More recently, Sandroff et al. examined the validity of the measure relative to other performance measures used for patients with MS as well as its predictive capacity. Using a cohort of 96 patients with MS, the authors performed the SSST along with the 25FWT, Timed Up and Go (TUG) test, and 6MWT. Expectedly, the correlations between the SSST and these more established measures were very high.

Figure 1

More importantly, performance on the SSST was observed to be 27 percent more precise than the 25FWT and 9 percent more precise than the TUG test in discriminating between mild (EDSS scores 2.0-3.5), moderate (EDSS scores 4.0-5.5), and severe (EDSS scores 6.0-6.5) MS. It was also 22 percent more precise than the 25FWT and 33 percent more precise than the TUG test at discriminating between patients with MS who had a high versus low fall risk. If you want a nuanced look at ambulatory ability in patients with MS and its relationship to disability and fall risk, the SSST appears to be quite informative.

What's more, it appears to be sensitive to differences in presentation. For example, the average SSST time for those at elevated fall risk (Activities-specific Balance Confidence (ABC) Scale scores below 69) was 14 seconds, while for those who were not at a fall risk, the average time was about 9 seconds. Similarly, average SSST times of 7, 9.5, and 15 seconds were associated with mild, moderate, and severe MS (Table 2).

Table 2

This suggests an instrument that could be used to demonstrate the value of a lower-limb orthosis irrespective of its direct impact on EDSS classification. For example, a patient who presents with an SSST time of 14 seconds would be seen as severely disabled with a high fall risk. If that patient then receives an AFO that allows him or her to reduce the timed performance on the SSST to 9 seconds, his or her performance would now be viewed as moderately disabled with a low fall risk. Within this paradigm, the AFO could be viewed by the medical community as an asset rather than a liability.

Busting the Disability Myth

In our current healthcare climate, each profession has to demonstrate its value. This is precluded when the modality is defined as a marker of disability. It is enabled when measures exist that predict things like disability and fall risk and have the potential of being positively influenced by the intervention used. The SSST appears to be a possible avenue for helping the MS medical community appreciate the value of lower-limb orthoses in reducing, rather than defining, disability.

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

References

  1. Kurtzke, J. F. 1983. Rating neurologic impairment in multiple sclerosis: An expanded disability status scale (EDSS). Neurology 33 (11):1444-52.
  2. Stellmann, J. P., A. Neuhaus, N. Götze, S. Briken, C. Lederer, M. Schimpl, C. Heesen, and M. Daumer. 2015. Ecological validity of walking capacity tests in multiple sclerosis. PLoS ONE 10 (4):e0123822. Doi:10.1371/journal.pone.0123822.
  3. Preiningerova, J. L., K. Novotna, J. Rusz, L. Sucha, E. Ruzicka, and E. Havrdova. 2015. Spatial and temporal characteristics of gait as outcome measurements in multiple sclerosis (EDSS 0 to 6.5). Journal of NeuroEngineering and Rehabilitation 12:14. Doi 10.1186/s12984-015-0001-0.
  4. Niewenhuis, M. M., H. Van Tongeren, P. S. Sørensen, and M. Ravnborg. 2006. The six spot step test: A new measurement for walking ability in multiple sclerosis. Multiple Sclerosis 12 (4):495-500.
  5. Sandroff, B. M., R. W. Motl, J. J. Sosnoff, J. H. Pula. 2015. Further validation of the Six-Spot Step Test as a measure of ambulation in multiple sclerosis. Gait & Posture 41 (1):222-7.