Cryptogenic organizing pneumonia (COP), the idiopathic form of organizing pneumonia (formerly called bronchiolitis obliterans organizing pneumonia or BOOP), is a type of diffuse interstitial lung disease that affects the distal bronchioles, respiratory bronchioles, alveolar ducts, and alveolar walls [1-7]. The primary area of injury is within the alveolar wall.
In addition to the cryptogenic form, secondary organizing pneumonia can be seen in association with connective tissue diseases, a variety of drugs, malignancy, and other interstitial pneumonias [2,8].
Cryptogenic organizing pneumonia will be reviewed here. The other idiopathic interstitial pneumonias and an approach to the evaluation and diagnosis of interstitial lung disease in adults are discussed separately. (See "Idiopathic interstitial pneumonias: Clinical manifestations and pathology" and "Approach to the adult with interstitial lung disease: Clinical evaluation" and "Approach to the adult with interstitial lung disease: Diagnostic testing".)
The American Thoracic Society (ATS) and European Respiratory Society (ERS) statement on the classification of idiopathic interstitial pneumonias, as well as other ATS guidelines, can be accessed through the ATS web site at www.thoracic.org/statements.
The exact incidence and prevalence of COP are unknown. A cumulative incidence of six to seven cases per 100,000 hospital admissions was found at a major teaching hospital in the United States , while in a 20 year review of national statistics for Iceland, the mean annual incidence was 1.1 per 100,000 . In separate reports, approximately 56 to 68 percent of OP cases have been deemed cryptogenic rather than secondary [10,11].