In patients with systemic sclerosis (SSc), the 6-minute walk distance (6MWD) has demonstrated strong reproducibility and the 6 minute walk test (6MWT) has shown utility as a valid tool for assessing overall prognosis and functional capacity of patients with SSc, according to the results of a prospective, observational cohort study published in The Journal of Rheumatology.
Over a 6-year period, patients with SSc who underwent ≥2 6MWT evaluations within a minimum 3-month interval, along with simultaneous routine clinical, biologic, and functional evaluations, were enrolled consecutively in the study. Each 6MWT evaluation was repeated 2 times to assess the reproducibility of the 6MWD, with the highest value reported for the analysis.
A total of 56 participants were included in the study, 38 of whom were women. The mean patient age was 46±12.7 years. The modified Rodnan skin score was 17±10 and the Scleroderma Health Assessment Questionnaire was 1±0.8 at first referral. Overall, 277 6MWT assessments (5±3.9 6MWTs per patient) were conducted over 23±22.5 months of follow-up.
The mean 6MWD absolute value was 457±117 m, with a mean Borg dyspnea score of 4±2.2. The 6MWD intraclass correlation coefficient was 0.996 (95% CI, 0.995-0.999; P <.0001), which demonstrated strong reproducibility. According to multivariate linear regression analysis, the following factors were independently associated with a lower 6MWD: sex (P <.0001), mRSS (P =.008), tendon friction rub (P =.003), SHAQ (P =.02), muscle disability score (P =.03), diffusing capacity of carbon monoxide (P =.0008), and left ventricular ejection fraction (P =.006).
At first referral, the 6MWD was an independent predictor for overall mortality (hazard ratio [HR], 0.99; 95% CI, 0.988-0.999) and for SSc-related mortality (HR, 0.99; 95% CI, 0.988-0.999).
The investigators noted that patients with very advanced disease are unable to perform the 6MWT because of muscle weakness, joint pain, or foot calcinosis. They added that although the 6MWD reproducibility was strong in the study population, the 6MWT does not cover the entire range of patients with SSc.
Pugnet G, Marjanovic Z, Deligny C, et al. Reproducibility and utility of the 6-minute walk test in systemic sclerosis [published online July 1, 2018]. J Rheumatol. doi: 10.3899/jrheum.170994