Usual Interstitial Pneumonia

Abstract

Idiopathic pulmonary fibrosis (IPF), the most common and severe among idiopathic interstitial pneumonias, has now been definitively recognized as a distinct clinical entity, defined in the American Thoracic Society/European Respiratory Society (ATS/ERS) consensus statement as a specific form of chronic fibrosing interstitial pneumonia limited to the lung and associated with the histologic appearance of usual interstitial pneumonia (UIP) in surgical lung biopsy material.1, 2, 3 Thus, the precise definition of the “UIP” pattern is crucial for the diagnosis of IPF when histology is available and also for the understanding of the specific changes characterizing this devastating disease. The morphologic criteria for defining the UIP pattern have been progressively refined, from the seminal studies of Liebow to the recent ATS/ERS classification. It is worth noting that the different morphologic patterns that characterize the idiopathic interstitial pneumonias—UIP, nonspecific interstitial pneumonia (NSIP), acute interstitial pneumonia (AIP), cryptogenic organizing pneumonia (COP), lymphocytic interstitial pneumonia (LIP), desquamative interstitial pneumonia (DIP), and respiratory bronchiolitis-combined interstitial lung disease (RB-ILD)—have been progressively defined following a process of matching the clinical, radiologic, and morphologic features, using varying terms and criteria, in the absence of a precise knowledge of the etiology and pathogenesis of the different diseases.