Background: Progressive pulmonary fibrosis (PPF) is possible among patients with connective tissue disease (CTD) related interstitial lung disease (ILD). We aimed to compare the prevalence and clinical characteristics of patients with CTD-ILD, with and without PPF, according to the different diagnostic criteria currently used in practice.

Methods: This retrospective study included patients diagnosed with CTD-ILD, with a ?1-year follow-up of their lung function, at a single tertiary hospital in South Korea. Diagnostic criteria from three clinical trials and from a recently updated guideline were applied.

Results: Of the 110 patients included, the prevalence of CTD-ILD with PPF for the different diagnostic criteria was as follows: RELIFE, 25.2%; INBUILD, 23.6%; TRAIL1, 22.4%; and ATS/ERS/JRS/ALAT, 38.3%. A previous history of pulmonary tuberculosis and less positivity for antinuclear antibodies were identified in the PPF group. The radiologic pattern of ILD did not differ between patients with and without PPF, with a usual interstitial pneumonia pattern identified in 34.6% of the patients, independent of the diagnostic criteria used. Systemic steroids and immunomodulatory agents were used in about 80% of patients with PPF and 50% without PPF, irrespective of the diagnostic criteria used. Antifibrotic therapy was used in a limited number of patients in both groups.

Conclusions: The proportion of patients with CTD-ILD and PPF was higher for the recent guideline criteria, without a between-group difference in clinical characteristics.