Use of 6-minute walk distance to predict lung transplant-free survival in fibrosing non-IPF interstitial lung diseases.

BACKGROUND AND OBJECTIVE: The identification of progression in patients with fibrosing non-idiopathic pulmonary fibrosis (IPF) interstitial lung diseases (ILDs) represents an ongoing clinical challenge. Lung function decline alone may have significant limitations in the detection of clinically significant progression. We hypothesized that longitudinal changes of 6-min walk distance (6MWD) from baseline, simultaneously considered with measures of lung function, may independently predict survival and identifying clinically significant progression of disease. METHODS: Forced vital capacity (FVC), diffusing lung capacity (DLCO) and 6MWD were considered both at baseline and at 1 year in a discovery cohort (n = 105) and in a validation cohort (n = 138) from different centres. The primary endpoint was lung transplant (LTx)-free survival. RESULTS: Average follow-up was 3 years in both cohorts. Combined incidence of deaths and LTx was 29% and 21%, respectively. No collinearity and no strong correlations were observed among FVC, DLCO and 6MWD longitudinal changes. While age, gender and BMI were not significant, 6MWD decline ≥24 m predicted LTx-free-survival significantly and independently from FVC and DLCO declines, with high sensitivity and specificity, in both the discovery and the validation cohorts. Although FVC and DLCO declines remained significant predictors of LTx-free survival, 6MWD decline was more accurate than the proposed ATS/ERS/JRS/ALAT functional criteria. Results were confirmed after stratifying patients by baseline FVC. CONCLUSION: Longitudinal declines of 6MWD are associated with poor survival in fibrosing ILDs across a wide range of baseline severity, with high accuracy. 6MWD longitudinal decline is largely independent from lung function decline and may be integrated into the routine assessment of progression.

Percent Predicted vs. Absolute Six-Minute Walk Distance as Predictors of Lung Transplant-Free Survival in Fibrosing Interstitial Lung Diseases.

INTRODUCTION: Fibrosing interstitial lung diseases (ILDs) often progress despite treatment and become life-threatening, with lung transplant (LTx) remaining the only curative option. Six-minute walk distance (6MWD) is increasingly recognized as reliable predictor of clinical course, especially when longitudinally considered. The use of reference equations to express 6MWD as percent predicted (6MWD%) has not been previously studied in fibrosing ILDs. We sought to investigate whether the prognostic power of 6MWD% is superior to that of 6MWD expressed in meters (6MWD-m). METHODS: A retrospective, multicenter cohort analysis was conducted on both idiopathic pulmonary (IPF) and non-IPF fibrosing ILD patients. Patients were divided into a discovery (n = 211) and a validation (n = 260) cohort. Longitudinal changes of 6MWD% and lung function parameters were simultaneously considered. LTx-free survival at 3 years from baseline was the endpoint. Competing risks of death and LTx were considered. RESULTS: Baseline 6MWD% and its longitudinal changes were significant predictors of LTx-free survival and independent from lung function variables. In both cohorts, on multivariate cox proportional hazard regression analysis, receiver operating characteristics analysis and Kaplan-Meier estimates, 6MWD% was consistently, but only slightly superior to 6MWD-m as a predictor of LTx-free survival. CONCLUSION: 6MWD% has only a slight, yet detectable advantage over 6MWD-m as a predictor of survival in fibrosing ILDs. Utilizing 6MWD% may aid in risk stratification, treatment monitoring, and LTx timing optimization. However, available reference equations do have predicting limitations. Refined predictive equations and standardizing reporting practices are therefore needed to further enhance the clinical utility of 6MWD% in fibrosing ILDs.