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 recognising 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 versus 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.