In a European Respiratory Journal (ERS) article, Christopher J. Ryerson, MD, and colleagues propose an update to the classification of interstitial pneumonias.1 This update builds on the previous American Thoracic Society/ERS statement from 2013 with the inclusion of both idiopathic and nonidiopathic/secondary interstitial pneumonias, the introduction of new terminology, the subclassification of interstitial and alveolar filling processes, and the recommendation to use confidence level in diagnosis to guide further evaluation and management.
This consensus statement required more than 70% agreement among the interstitial lung disease (ILD) experts selected for the committee—who considered the current literature and expert consensus in making recommendations—but it did not require a systematic review.
One of the major recommendations is the introduction of the term “bronchiolocentric interstitial pneumonia” (BIP) to describe an airway-centric process of interstitial pneumonia or fibrosis and also includes the radiologic and histologic features that can be seen in hypersensitivity pneumonitis (HP). The authors propose BIP as an overarching term that encompasses HP and other conditions with similar histological and radiological features, such as systemic autoimmune rheumatic disease-associated ILD (SARD-ILD), aspiration, and medication exposures. In addition, because a proportion of HP cases may lack an identifiable antigen yet exhibit typical radiologic features of HP, the authors propose using HP in these situations only if there is multidisciplinary diagnosis consensus or histologic features, such as granulomatous inflammation in an airway-centric distribution, suggesting HP. The authors suggest making this distinction because in patients with chronic aspiration, SARD-ILD, or medication exposures, there can be an airway-centric process, but not necessarily be HP.
However, because there is no clear implication for prognosis, evaluation, or management associated with the term, the relevance of switching to the BIP terminology remains unclear. In fact, there was dissent within the committee: Four members did not include themselves as coauthors due to disagreement on this topic.
Similarly, the authors also introduce the term “alveolar macrophage pneumonia” as a substitute for desquamative interstitial pneumonia to describe diffuse alveolar macrophage accumulation within alveoli, as seen mostly in people who smoke but also less commonly in SARD, occupational exposures, or surfactant metabolism disorders.
The authors recommended replacing acute interstitial pneumonia (AIP) with diffuse alveolar damage (DAD) because AIP is not always an acute process. In addition, this can represent an acute exacerbation of an underlying ILD and can be characterized as DAD on histopathology.
The article also describes the histopathologic and radiologic features that characterize the various ILD patterns, classifying them based on the involvement of the interstitial and alveolar spaces, although most conditions involve both to some extent.
In addition, the committee has raised research questions for each of these topics that require further work. However, the utility of this classification for diagnosis, evaluation, and management, as well as its impact on prognostication, remains unclear. It remains to be seen whether this updated terminology will affect current clinical care or research.
References
1. Ryerson CJ, Adegunsoye A, Piciucchi S, et al. Update of the international multidisciplinary classification of the interstitial pneumonias: an ERS/ATS statement. Eur Respir J. 2025;66(6). doi:10.1183/13993003.00158-2025
