Substituting bronchiolocentric interstitial pneumonia for hypersensitivity pneumonitis: a word of caution

Extract The 2025 update to the 2013 classification of interstitial pneumonias (IPs) introduces bronchiolocentric IP (BIP) as a major pattern and idiopathic BIP as a provisional entity that replaces a multidisciplinary discussion (MDD) diagnosis of hypersensitivity pneumonitis (HP), as defined by previously published diagnostic criteria in patients without an identified exposure [1]. Other proposed changes include extending the classification of IP to entities of known aetiology, replacing desquamative IP (DIP) and acute IP (AIP) with the terms alveolar macrophage pneumonia (AMP) and idiopathic diffuse alveolar damage (DAD), respectively, grouping AMP and organising pneumonia with other alveolar filling patterns (eosinophilic pneumonia, pulmonary alveolar proteinosis, lipoid pneumonia), subcategorising interstitial and alveolar filling patterns into nonfibrotic and fibrotic subgroups, and formalising consideration of diagnostic confidence in patient evaluation and management. The 2025 update, like its predecessors, was developed by consensus among experts to offer standardised terminology and diagnostic criteria supported by evidence of variable quality. In this context, consensus is a process in which differences of opinion are resolved through iterative discussion and voting. It differs from a simple democratic process in that it carries an expectation that any differences of opinion that remain are sufficiently narrow that all participants will advocate for the recommendations. As actively engaged project participants from start to finish, we endorsed the process by which competing opinions were addressed followed by peer review from qualified experts. While commentary to address the most significant of these changes may provide more clarity for the application of principles and terminology to a broader group of predominantly diffuse and occasionally localised disorders, we withdrew as authors of the published manuscript, not because of differences in opinion but rather our inability to authentically advocate for: 1) introduction of BIP as a “major” pattern, and 2) idiopathic BIP as a provisional clinical entity. As co-authors of diagnostic HP guidelines, we believe that introducing idiopathic BIP while replacing HP with “BIP pattern” to report radiological and biopsy findings may diminish motivation to relentlessly pursue a potential cause in some HP patients [2, 3].