Proposed new classification of idiopathic interstitial pneumonias

Abstract

This presentation reviews the histopathology of the IIPs since the 2002 ATS/ERS classification of IIPs in the light of the 2013 update. The seven histological patterns proposed in 2002 remain, with diagnostic criteria refined but overall unchanged. A multidisciplinary approach is now established as best practice. NSIP is now recognised as a distinct clinicopathological entity. Respiratory bronchiolitis-interstitial lung disease (RB-ILD) is now commonly diagnosed without the need for surgical biopsy. A diagnostic algorithm has been proposed for the correlation of surgical biopsies with imaging in relation to patients with suspected idiopathic pulmonary fibrosis (IPF). Acute exacerbation of IIPs is now well-defined. Some IIP patients remain hard to classify, often due to overlap of patterns, and a classification based on observed disease behaviour is proposed for such patients. Pleuroparenchymal fibroelastosis is included as a rare but distincty clinincopathological entity. Acute fibrinous organising pneumonia and bronchiolocentric interstitial pneumonia are proposed as histologic patterns that may be of benefit in biopsy classification prior to multidisciplinary review, but are not sufficiently characterized to be recognised as distinct clinical entities.