Clinical and histologic spectrum of bronchiolitis obliterans, including bronchiolitis obliterans organizing pneumonia

'Bronchiolitis obliterans' is a term that has been used to describe clinical syndromes as well as histologic lesions. In many instances its usage is confusing, particularly when it is applied to localized lesions. The term 'bronchiolitis obliterans' should only be used in well-defined contexts, and it should be stated whether it is being used in a clinical or a histologic sense. When used histologically, an attempt should be made to separate proliferative bronchiolitis obliterans, a common nonspecific reparative reaction, from constrictive bronchiolitis, a lesion that is associated with clinical evidence of airflow obstruction. The term 'BOOP' or idiopathic BOOP should be reserved for a distinct clinicopathologic entity that has a characteristic, but not specific, histologic appearance; because of confusion with these terms we recommend consideration of using the designation cryptogenic organizing pneumonitis.