Patterns of lung fibrosis in patients with interstitial pneumonia with autoimmune features and connective tissue diseases-associated interstitial lung disease-a narrative review.

Interstitial pneumonia with autoimmune features (IPAF) was defined in 2015 as a research statement of European Respiratory Society and American Thoracic Society. Connective tissue diseases (CTDs) manifest in the respiratory tract, the main manifestation being interstitial lung disease, which contributes to morbidity and mortality. This poses numerous clinical challenges and is a substantial burden on healthcare systems around the world. The objective of this narrative review was to provide readers with a comprehensive and extensive overview of such manifestations in the respiratory system, analysis of prevalence of specific manifestations in the lung and to characterize population of patients with IPAF. We reviewed the current state of knowledge on radiological findings in interstitial lung diseases in course of convective tissue diseases and IPAF, a narrative review of PubMed database using Advanced Search Builder was performed. The search was conducted from 15.07.2021 to 03.04.2022. A total of 655 articles in English were reviewed. Similarities and differences between interstitial pneumonia in course of well-established CTDs and IPAF are discussed with special emphasis on required future research areas. Manifestations of CTDs in the respiratory system are overviewed, with the emphasis on interstitial lung disease, as despite clinical similarities of various connective tissue diseases, there is variability in their presentation in the respiratory system, radiological patterns and clinical outcomes. We would also like to draw readers' attention to clinical significance of interstitial lung abnormality both in the context of CTDs and lack of underlying autoimmune disorders. There is need for prospective cohort studies regarding the natural course of IPAF, its clinical stability and its manifestations in the respiratory system. Prospective studies are also required to evaluate diagnostic and prognostic factors of IPAF. Interstitial lung disease associated with CTDs (CTD-ILD) is a significant factor impacting clinical outcomes and patient prognosis, therefore its diagnostic work-up is best performed by an experienced multidisciplinary team and with use of procedures of high diagnostic yield.