MONTREAL—A modified version of the Six-Minute Walk Test (6MWT) may measure walking disability in patients with multiple sclerosis (MS) more precisely than the tests currently used for this purpose, according to research presented at the 25th Annual Meeting of the Consortium of Multiple Sclerosis Centers.
“The 6MWT is feasible and tolerated in subjects with MS, including those in the upper Expanded Disability Status Scale (EDSS) range of 4.0 to 6.5,” said Myla Goldman, MD, of the Department of Neurology at the University of Virginia in Charlottesville. “The 6MWT and the Timed 25-Foot Walk (T25FW) are well-correlated variables, but overall, the 6MWT appears to have increased precision in identifying EDSS subgroups.”
Dr. Goldman and colleagues came to these conclusions by testing the 6MWT, which historically has been used in patients with respiratory or cardiac disease, in a cohort of 96 patients with MS.
In addition to showing greater precision than the T25FW, the 6MWT correlated fairly well with the Multiple Sclerosis Walking Scale-12 (MSWS-12), a subjective measure of MS walking disability.
The Search for an Alternative Measure
The currently accepted measures of MS walking disability all have important limitations, according to Dr. Goldman. Some patients with mild MS may have walking difficulties below the threshold detectible by the T25FW (the ambulatory component of the Multiple Sclerosis Functional Composite) or the EDSS ambulatory component, she said, adding that the EDSS’s compression of data into ordinal variables limits its sensitivity. Because the MSWS-12 depends on subjective reports from patients, she added, it needs to be considered in conjunction with more objective measures.
With these limitations in mind, the researchers turned to the 6MWT, which determines walking capacity by having subjects walk as far as they can in six minutes. The test is administered on an indoor walking course of at least 30 meters, and persons are asked to pivot and continue to walk whenever they reach an end of the course. The primary outcome is total distance walked, but other assessed outcomes can include subjects’ heart rate, dyspnea, fatigue, and oxygen saturation before and after the test; stopping or pausing during the test; and symptoms of angina, dizziness, or pain at the end of the test.
In a 2008 study, Dr. Goldman and colleagues used a modified version of the 6MWT to test 40 patients with MS and 20 healthy controls. The modified version differed from the regular 6MWT in that subjects were told to walk as quickly as possible, were not told that they could rest during the test, and were not offered encouragement during the test.
Among the patients with MS, total 6MWT distance decreased with increasing disability, the 6MWT showed excellent intra-rated and inter-rated reliability, and subjective measures of ambulation and fatigue were more closely correlated with 6MWT results than with EDSS results. The researchers concluded that the modified 6MWT “is a feasible, reproducible, and reliable measure in MS.”
However, only six of that study’s 40 participants with MS had severe disease. “So while this work was valuable, one of its limitations was in determining the feasibility of the 6MWT in a more advanced, ambulatory-impaired MS population,” Dr. Goldman noted.
A 41% Increase in Precision
In the current study, Dr. Goldman and colleagues investigated the modified 6MWT’s utility in a population of 96 participants with confirmed MS, ensuring that their cohort included a high percentage of patients with severe disease. Of the study participants, 30 had mild MS (EDSS scores of 2 to 3.5), 29 had moderate MS (scores of 4 to 5.5), and 37 had severe MS (scores of 6 to 6.5). The subjects were evaluated with the 6MWT, the T25FW, and the MSWS-12.
A majority of participants were female, and an overwhelming majority were white. Their mean duration of MS was 11.8 years, 82% of them had relapsing-remitting MS, and 80% were receiving disease-modifying therapy. All of the subjects walked continuously for the full six minutes of the 6MWT.
Their total distance on the 6MWT was inversely correlated with their EDSS status, the researchers found. Among the total cohort, results on the 6MWT and the T25FW were strongly and significantly correlated, noted Dr. Goldman.
However, the 6MWT was 41% more precise than the T25FW in identifying EDSS subgroups. Although the 6MWT was able to distinguish between all of these subgroups, the T25FW was unable to distinguish between the mild and moderate subgroups.
Both the 6MWT and the T25FW were correlated with the overall cohort’s self-reports on the MSWS-12, but not with those of the mild or severe subgroups. These disparities were driven by the MSWS-12 questions about patients’ use of walking support, according to Dr. Goldman.