Statement der ExpertInnengruppe „Interstitielle Lungenerkrankungen und Orphan Diseases“ der Österreichischen Gesellschaft für Pneumologie zum Update der internationalen multidisziplinären Klassifikation der interstitiellen Pneumonien 2025

The update of the American Thoracic Society/European Respiratory Society (ATS/ERS) classification of interstitial pneumonias published in 2025 extends the oprior classification system beyond merely idiopathic entities, now also encompassing entities with identifiable triggers [1]. The core component of this update is the terminological reorientation of the classification towards a descriptive, primarily morphologically oriented concept with the aim of a clear differentiation of radiological and histological patterns from clinically defined diseases. Acute interstitial pneumonia (AIP) is now designated as idiopathic diffuse alveolar damage (DAD), and desquamative interstitial pneumonia (DIP) as alveolar macrophage pneumonia (AMP). The pattern of bronchiolocentric interstitial pneumonia (BIP) has been introduced as an independent morphological pattern, reserving the term hypersensitivity pneumonitis (HP) exclusively for multidisciplinary diagnosis in the future. Furthermore, the updated classification provides a biologically founded and clinically applicable categorization system of interstitial and alveolar filling patterns and the prognostically relevant separation into fibrotic and nonfibrotic phenotypes. Also, there is a stronger emphasis on the transparent reporting of the diagnostic confidence by interstitial lung disease (ILD) boards, including the use of "provisional" diagnoses or of the term "unclassifiable ILD" in cases of low and very low diagnostic certainty. The current classification can help to standardize the diagnostic course and to make the decision-making process in the ILD board more transparent. It is to be expected that this update will be the foundation for future research and for new knowledge in the field of ILD. In addition, it should however not be ignored that the new classification has been critisized by some experts with respect to the introduction of the pattern of BIP and the provisional entity of "idiopathic BIP". It is feared that this change in terminology emphasizing the morphological pattern rather than causative factors could lead to reduced attention concerning potential trigger exposures in the diagnostic process.