Clinical Impact of Progressive Pulmonary Fibrosis in Systemic Sclerosis-associated Interstitial Lung Disease

<bold>Background:</bold> Progressive pulmonary fibrosis (PPF) includes various fibrotic interstitial lung diseases (ILDs) that worsen despite standard treatment. We aimed to investigate the prevalence, clinical characteristics, and survival of PPF in Korean patients with systemic sclerosis (SSc) associated ILD patients. <bold>Methods:</bold> Clinical data from patients with SSc-ILD were retrospectively collected. The PPF was defined according to the criteria proposed by the American Thoracic Society, European Respiratory Society, Japanese Respiratory Society, and Latin American Thoracic Association. <bold>Results:</bold> Among a total of 101 patients, the mean age was 52.6 years, 80.2% were female and 26.7% were identified as having PPF. At baseline, the PPF group had a lower minimum oxygen saturation (SpO2) during the six-minute walking test (6MWT) (88.0 vs. 92.7 %, P=0.015) than the no-PPF group. However, at one year follow-up, the PPF group had significantly greater changes in FVC (−5.4 vs. 3.5 % predicted, P<0.001) and DLCO (−8.2 vs. 2.3 % predicted, P<0.001) than the no-PPF group. Multivariate logistic regression analysis showed that minimum SpO2 during 6MWT was independently associated with PPF (odds ratio, 0.930; 95% confidence interval [CI], 0.868-0.996, P=0.038). Kaplan-Meier analysis showed worse survival in the PPF group (median: 210 months vs. not reached, P=0.014). Multivariable Cox regression adjusting for age, sex, body mass index, lung function, and minimum SpO2 during 6MWT showed that PPF was independently associated with mortality (hazard ratio, 3.942; 95% CI, 1.601-9.709, P=0.003). <bold>Conclusion:</bold> Our data suggest that around a quarter of SSc-ILD patients had PPF and have a poor survival outcome.