Update on idiopathic interstitial pneumonias

Abstract

The idiopathic interstitial pneumonias (IIPs) comprise a major portion of diffuse infiltrative (interstitial) lung diseases. The classification of IIPs was initially conceived 4 decades ago and has undergone revisions over the intervening years with the most recent version published in 2013. Current classification distinguishes “major” forms of IIPs(idiopathic pulmonary fibrosis, idiopathic nonspecific interstitial pneumonia, respiratory-bronchiolitis-interstitial lung disease, desquamative interstitial pneumonia, cryptogenic organizing pneumonia, and acute interstitial pneumonia) from “rare” forms (idiopathic lymphoid interstitial pneumonia, idiopathic pleuroparenchymal fibroelastosis). In addition, the category of “unclassifiable” IIP is introduced in recognition of IIP cases that remain difficult to classify even with the current scheme. This review describes the historical background for IIPs, current perspectives, and summarizes the clinical-pathologic entities included in the current classification scheme.