Reproducibility and Utility of the 6-minute Walk Test in Systemic Sclerosis

Objective. To assess the reproducibility and the utility of the 6-minute walk test (6MWT) in systemic sclerosis (SSc). Methods. All patients with SSc who underwent at least two 6MWT within a minimum 3-month interval plus simultaneous routine clinical, biological, and functional evaluations were consecutively enrolled in this observational study over 6 years. Following American Thoracic Society guidelines, each 6MWT was repeated twice to assess the 6-minute walk distance (6MWD) reproducibility, with the highest value being reported for subsequent analysis. Results. Among 56 (38 female) included patients aged 46 +/- SD 12.7 years, with 17 +/- 10 modified Rodnan skin score (mRSS) and 1 +/- 0.8 Scleroderma Health Assessment Questionnaire (SHAQ) at first referral, 277 6MWT evaluations (5 +/- 3.9 6MWT per patient) were performed over 23 +/- 225 months followup. Meanwhile, 8 deaths (87.5% SSc-related) occurred. The mean 6MWD absolute value was 457 +/- 117 m with a 4 +/- 2.2 mean Borg dyspnea score. The 6MWD intraclass correlation coefficient was 0.996 (95% CI 0.995-0.999, p < 0.0001). In multivariate linear regression analysis, these factors were independently associated with a lower 6MWD: sex (R-2 = 0.47, p < 0.0001), mRSS (R-2 = 0.47, p = 0.008), tendon friction rub (R-2 = 0.47, p = 0.003), SHAQ (R-2 = 0.47, p = 0.02), muscle disability score (R-2 = 0.47, p = 0.03), DLCO% (R-2 = 0.47, p = 0.0008), and left ventricular ejection fraction (R-2 = 0.47, p = 0.006). The 6MWD at first referral was an independent predictor for the overall mortality (IIR 0.99, 95% CI 0.988-0.999) and the SSc-related mortality (HR 0.99, 95% CI 0.988-0.999). Conclusion. We show strong reproducibility for the 6MWD and confirm the 6MWT utility to assess the overall prognosis of patients with SSc.