Background: Connective tissue disease associated interstitial lung disease (CTD-ILD) may progress. Understanding risk of progression is important for prognosis, treatment and planning of clinical trials.

Objective: Assess ILD progression across CTD subtypes.

Methods: CTD-ILD patients (N=504) from a Norwegian and Swiss cohort were included. ILD progression was assessed over 12 months on standard of care treatment and defined as absolute FVC decline?10% and according to progressive pulmonary fibrosis (PPF) criteria. Prediction of progression across CTD-ILD subtypes was assessed by logistic regression adjusted for risk factors and treatment.

Results: Overall, 57 (13.7%) had an FVC decline?10% and 47 (12%) met PPF criteria. Absolute FVC decline varied by CTD-ILD subtype. PPF occurred most frequently in SSc and pSS, and FVC decline?10% was most frequent in MCTD and SSc (Figure). There was no difference in occurrence of PPF (OR1.00, 95%CI 0.54-1.86, p=0.995) in patients treated vs not treated with immunosuppressives. However, we observed less FVC decline?10% (OR 0.51, 95%CI 0.28-0.90, p=0.02) in treated patients. The CTD subtypes had different treatment patterns, with the majority of RA and ASS patients being treated.

Conclusion: ILD progression varied between CTD subtypes. This may have implications for prognosis and treatment of individual patients and inclusion of CTD-ILD patients in clinical trials.