Limitations of 6-minute Walk Test Reference Values for Spinal Muscular Atrophy
The 6-minute walk test (6MWT) is frequently used to assess the ambulatory function in those with spinal muscular atrophy (SMA). With the trajectory of the disease showing improvements in gait patterns as treatments have become more effective, it is important that we are using appropriate healthy reference range values for the 6MWT to adequately assess progression in this population. This article aims to determine an appropriate healthy reference range to use for individuals with SMA.
Nine articles were chosen for the systematic review after the inclusion and exclusion process. Of the 9 articles chosen, 3 viewed a healthy pediatric population (age range 3-19) and 6 viewed a healthy adult population (age range 20-81).
The researchers performed a systematic review of articles attempting to determine normative values for the 6MWT on healthy adults and/or children. The studies chosen for the review were selected from PubMed and Scopus databases using the following keywords: “6MWT”, “six minute walk test”, “healthy”, “reference”. Studies were required to follow the American Thoracic Society protocol for the 6MWT as well as provide a reference value equation. Each study was also required to analyze both sexes and have a healthy adult and/or children population included. In order to apply the SMA data to the studies chosen for the systematic review, 6MWT data for individuals diagnosed with SMA was obtained from a retrospective chart review (2008-2017) at Columbia University Irving Medical Center Neuromuscular Clinic in New York.
Reference equation for 6-minute walk distance and corresponding predictor variables (age, gender, height, weight, etc.)
The studies chosen for the systematic review produced variant calculations of predicted 6-minute walk distances in both pediatric and adult populations. Thus, at this time there is still not a specific reference equation to be considered when evaluating the function of SMA patients.
Consistency in 6MWT protocol for selected articles
Representation of both sexes and all age participants in populations selected
Articles included in the systematic review were only in English.
Small sample size of clinical SMA Data
Race/Ethnicity not available in SMA data
The systematic review performed in this study was not able to determine an appropriate reference value for the 6MWT in individuals with a diagnosis of SMA. Further evaluation is required to determine an appropriate 6MWT reference value for SMA. Typical predictive variables for the 6MWT in healthy adults/children may not be appropriate for this population such as the use of height and weight due to changes related to the disease. Future studies should consider a more extensive list of variables that can be applied to this population.