Update of the International Multidisciplinary Classification of the Interstitial Pneumonias: An ERS/ATS Statement

Background: The 2013 American Thoracic Society/European Respiratory Society Statement on the classification of the idiopathic interstitial pneumonias described 6 major and 2 rare subtypes of idiopathic interstitial pneumonia, as well as recognizing unclassifiable disease. Objective: The objective of this statement is to update the 2013 classification of interstitial pneumonia. Methods: Five co-chairs identified a committee of 32 experts in the field as well as two individuals with lived experience. Creation of the document was supported by a series of video meetings, first including the full committee and then subgroups assigned to draft specific sections of the document. The classification scheme was developed by consensus. Results: The multidisciplinary committee of experts identified four major advances to the classification of interstitial pneumonia: (1) expansion beyond idiopathic interstitial pneumonias to also include secondary causes; (2) identification of new subcategories and updated terms, including addition of bronchiolocentric interstitial pneumonia as a major pattern as well as changing from acute interstitial pneumonia to idiopathic diffuse alveolar damage and desquamative interstitial pneumonia to alveolar macrophage pneumonia; (3) subclassification of interstitial and alveolar filling disorders, with interstitial disorders further subclassified as fibrotic vs non-fibrotic; and (4) consideration of diagnostic confidence in patient evaluation and management. The committee also provided a comprehensive update on the status of potential molecular tools and identified future research priorities. Conclusions: This update builds upon the previous classification approach by describing major advances in the classification of interstitial pneumonia over the last decade.