Update for pathologists on idiopathic interstitial pneumonias.

CONTEXT: Idiopathic interstitial pneumonias are a subset of diffuse pulmonary interstitial diseases classified by international consensus in 2002 as idiopathic pulmonary fibrosis, nonspecific interstitial pneumonia, cryptogenic organizing pneumonia, acute interstitial pneumonia, respiratory bronchiolitis interstitial lung disease, desquamative interstitial pneumonia, and lymphoid interstitial pneumonia. Each is associated with a characteristic histopathologic pattern. In 2011, updated consensus guidelines were released for diagnosis and management of idiopathic pulmonary fibrosis. The entire group of idiopathic interstitial pneumonias is currently undergoing refinement, with updates expected in a forthcoming consensus classification. Many of these recent and anticipated changes are relevant to pathologists.

OBJECTIVES: To review international consensus guidelines for diagnosis of idiopathic pulmonary fibrosis and other idiopathic interstitial pneumonias and to discuss recent and expected future classification updates.

DATA SOURCES: Published peer-reviewed literature and personal experience of the authors.

CONCLUSIONS: Diagnosis of idiopathic interstitial pneumonias by multidisciplinary discussion among clinicians, radiologists, and pathologists is now strongly encouraged. Diagnosis of idiopathic pulmonary fibrosis no longer requires surgical lung biopsy; high-resolution computed tomography is an acceptable surrogate. In the context of clinical trials, pathologists are being asked to assign levels of confidence for histologic diagnosis of usual interstitial pneumonia in patients with idiopathic pulmonary fibrosis. Acute exacerbation of idiopathic pulmonary fibrosis is now accepted and should be considered when acute lung injury is superimposed on a background of usual interstitial pneumonia. The updated classification of idiopathic interstitial pneumonias will include a separate category for rare entities, including lymphoid interstitial pneumonia and idiopathic pleuroparenchymal fibroelastosis.