Rationale: Different definitions to assess interstitial lung disease (ILD) progression in systemic sclerosis (SSc) have been proposed but not applied and compared in SSc-ILD yet.

Objective: To identify variables predicting SSc-ILD progression using three different definitions of progressive disease.

Methods: We included all SSc-ILD patients from the Oslo and Zurich cohorts. ILD progression was defined as (A) PPF ATS guideline criteria; (B) PF-ILD INBUILD criteria and (C) FVC decline >5%. Variables for ILD progression chosen by expert opinion were tested in multivariable logistic models adjusted for age, sex and treatment and models were tested using area under curve (AUC) with an AUC of 0.7 defined as acceptable.

Results: Of 231 included SSc-ILD patients 19% fulfilled the PPF, 39% the PF-ILD definitions and 31% showed FVC decline >5%. Multivariable logistic models for ILD progression defined as FVC>5% decline included baseline FVC, respiratory symptoms and the presence of anti-topoisomerase I antibody (ATA) and was considered as acceptable (AUC=0.70). The model for PF-ILD included diffuse cutaneous SSc (dcSSc), baseline FVC, respiratory symptoms and six-minute walking distance and had an acceptable AUC of 0.73. PPF was only predicted by reduced six minute walking distance, and the model was not acceptable (AUC=0.64).  

Conclusion: Progression is common in SSc-ILD, regardless of definition, but the PPF guideline criteria identified fewer progressors. We identified different variables predicting progression but could not identify a model with acceptable performance for PPF. This raises concerns about which definition to use in clinical practice and future studies.