Classification and Nomenclature of Interstitial Lung Disease

Abstract

Idiopathic pulmonary fibrosis (IPF) was first used in the mid-twentieth century as a term that referred to a seemingly unique lung disease entity characterized by diffuse interstitial changes on chest roentgenograms accompanied by both radiologic and histopathologic evidence of tissue fibrosis. However, as clinicians, radiologists, and pathologists evaluated patients and correlated clinical presentation with radiologic imaging and lung tissue specimens over the following decades, it became clear, especially to pathologists, that there were significant differences among cases of interstitial lung disease (ILD) that had been labeled with the diagnosis of IPF. Intense investigation over recent decades detected similarities and differences among various forms of ILD that led to an evolving nomenclature and classification system for these diverse entities, and the term IPF was retained for a specific entity characterized by a usual interstitial pneumonia (UIP) histopathologic pattern that is not explained by the presence of lung involvement due to a connective tissue disorder (CTD), a non-IPF form of idiopathic interstitial pneumonia (IIP), or other causes of interstitial pneumonia such as inhaled organic or inorganic environmental agents or an adverse reaction to a pharmacologic therapy.