Associations between 6-minute walk distance and physiologic measures and clinical outcomes in myositis-associated interstitial lung disease

OBJECTIVE: The 6-min walk test (6MWT) is a simple test widely used to assess sub-maximal exercise capacity in chronic respiratory diseases. We explored the relationship of 6-min walk distance (6MWD) with measurements of physiological, clinical, radiographic measures in patients with myositis-associated interstitial lung disease (MA-ILD). METHOD: We analysed data from the Abatacept in Myositis Associated Interstitial Lung Disease (Attack My-ILD) study, a 48-week multicentre randomized trial of patients with anti-synthetase antibodies and active MA-ILD. 6MWD, forced vital capacity (FVC), diffusing capacity (DLCO), high-resolution CT and various physician-/patient-reported outcome measures were obtained during the trial. Spearman's correlations and repeated-measures analysis with linear mixed-effects models were used to estimate the associations between 6MWD and various physiologic, clinical and radiographic parameters both cross-sectionally and longitudinally. RESULTS: Twenty participants with a median age of 57 years, 55% male and 85% white were analysed. Baseline 6MWD did not associate with baseline pulmonary function tests. Repeated-measures analysis showed 6MWD over time associated with FVC over time, but not with DLCO. 6MWD over time also correlated with University of California San Diego Shortness of Breath questionnaire dyspnoea score, Borg scores, as well as global disease activity and muscle strength over time. Emotional role functioning, vitality, general health and physical functioning scores by Short Form 36 also correlated with 6MWD over time. CONCLUSIONS: Exploratory work in a small cohort of MA-ILD demonstrated 6MWD over time associated with parallel changes in FVC and patient-reported outcomes of dyspnoea, but not with DLCO. Larger studies are needed to validate the reliability, responsiveness and utility of the 6MWT in MA-ILD. TRIAL REGISTRATION: ClinicalTrials.gov, http://clinicaltrials.gov, NCT03215927.