The classification, natural history and radiological/histological appearance of idiopathic pulmonary fibrosis and the other idiopathic interstitial pneumonias

The idiopathic interstitial pneumonias (IIPs) are a heterogeneous group of rare interstitial lung diseases (ILDs) or diffuse parenchymal lung diseases, which, as their name implies, are of unknown aetiology. The past 10 yrs have seen important advances in the classification of the IIPs into idiopathic pulmonary fibrosis (IPF) and its corresponding histopathological pattern of usual interstitial pneumonia (UIP), plus six non-IPF IIP subtypes. The present article will look at the current classification of IIPs, arising from the Consensus Statement of the American Thoracic Society and European Respiratory Society, and discusses the importance of differential diagnosis of IPF from the non-IPF IIP subtypes, especially nonspecific interstitial pneumonia. Diagnosis of IIPs is a dynamic process involving close collaboration between pulmonologists, radiologists and pathologists. Increasingly accurate diagnosis of IPF has been made possible by the use of high-resolution computed tomography (HRCT) and refinements in surgical lung biopsy. In IPF, a lung HRCT will typically reveal irregular reticular opacities, traction bronchiestasis and, most importantly, peripheral honeycombing. In contrast, histological examination shows evidence of UIP manifesting as typically subpleural and paraseptal established fibrosis, often with honeycomb changes, associated with mild chronic inflammation and varying numbers of fibroblastic foci in continuity with the edges of areas of established fibrosis. Despite these advances, obtaining a consistent and uniform diagnosis of idiopathic interstitial pneumonias is difficult, with studies showing significant disagreement in the diagnosis of interstitial lung diseases between academic centres of expertise and community-based clinicians. Greater interaction between academic and community clinicians, together with improved education, is needed to bridge this gap.