Diagnostic delay of associated interstitial lung disease increases mortality in rheumatoid arthritis: Spanish RA-ILD cohort

Introduction: Rheumatoid arthritis (RA) is a systemic autoimmune disease whose main extra-articular organ affected is the lung, sometimes in the form of diffuse interstitial lung disease (ILD) and conditions the prognosis. Methods: A multicenter, observational, descriptive and cross-sectional study of consecutive patients diagnosed with RA-ILD between 2013 and 2018. Demographic, analytical, respiratory functional and evolution characteristics were analyzed to evaluate the predictors of progression and mortality. Results: 106 patients were included. The mean age was 70.2±19.8 years and 51.9% of the patients presented UIP pattern. In the multivariate Cox analysis the age (HR 1.33, 95% CI 1.09-1.62, p=0.0045), the DLCO (%) (HR 0.85, 95% CI 0.73-0.98, p=0.0246), and the final SatO2 (%) in the 6MWT (HR 0.62, 95% CI 0.39-0.99, p=0.0465) were independent predictor variables of mortality, as well as the GAP index (HR 4.65, 95% CI 1.59 - 13.54, p=0.0051) and the CPI index (HR 1.12, 95% CI 1.03 - 1.22, p=0.0092). Also highlight that the diagnostic delay was an independent predictor of mortality (HR 1.11, CI 1.01-1.23, p = 0.035). Conclusions: This is the first study where it is objectified that the diagnostic delay in RA-ILD is associated with an increased mortality just like happens in IPF.