Cryptogenic organizing pneumonia (COP), formerly known as bronchiolitis obliterans organizing pneumonia, is a subacute pulmonary illness characterized by buds of granulation tissue in the bronchioles and alveolar ducts with extension of organization to the alveoli.1-2 It is an exceptionally rare extraintestinal manifestation of Crohn's disease (CD). The shared antigen theory may account for inflammation of both organ systems: decreased IgA secretion from mononuclear cells causes increased permeability to antigens such as bacteria, digestive enzymes and dietary antigens. The common embryonic origin of the Gl tract and the bronchial tree from the primitive foregut results in susceptibility of both systems to these antigen.We evaluated a 64 year old man with a history of CD maintained on mesalamine for ten years with dyspnea and productive cough for one month. Physical exam was significant for inspiratory crackles on both lung fields. Laboratory data showed leukocytosis with normal eosinophil count. A computed tomography (CT) scan of the chest revealed diffuse ground glass and nodular, opacities in bilateral perihilar and lower lung regions (Fig. 1A). Blood, urine, and bronchial cultures were all negative. Mesalamine was held due to concern for drug-induced lung disease. A transbronchial lung biopsy showed elongated "tongues" of loose organizing connective tissue within alveolar ducts typical of COP (Fig. 1B-C). The patient was started on prednisone with complete resolution of symptoms in three weeks. A follow-up CT scan one month after starting prednisone showed almost complete resolution of ground glass opacities in the lungs (Fig. 1D). Mesalamine was restarted without recurrence of pulmonary symptoms.
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