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Cryptogenic Organizing Pneumonia
(Bronchiolitis Obliterans Organizing Pneumonia)
Cryptogenic organizing pneumonia (COP) is an idiopathic condition in which granulation tissue obstructs alveolar ducts and alveolar spaces with chronic inflammation occurring in adjacent alveoli.
COP, a form of idiopathic interstitial pneumonia (see Overview of Idiopathic Interstitial Pneumonias), affects men and women equally, usually in their 40s or 50s. Cigarette smoking does not seem to be a risk factor.
About one half of patients recall having a community-acquired pneumonia-like syndrome (ie, a nonresolving flu-like illness characterized by cough, fever, malaise, fatigue, and weight loss) at the onset of the illness. Progressive cough and exertional dyspnea are what usually prompt the patient to seek medical attention. Chest examination demonstrates fine, dry, inspiratory crackles (Velcro crackles).
Diagnosis requires imaging tests and, if the diagnosis is not otherwise clear, surgical lung biopsy. Chest x-ray shows bilateral, diffuse, peripherally distributed alveolar opacities with normal lung volumes; a peripheral distribution similar to chronic eosinophilic pneumonia may occur (see Chronic Eosinophilic Pneumonia). Rarely, alveolar opacities are unilateral. Recurrent and migratory pulmonary opacities are common. Rarely, irregular linear or nodular interstitial opacities or honeycombing are visible at presentation. HRCT of the lung shows patchy airspace consolidation (present in 90% of patients), ground-glass opacities, small nodular opacities, and bronchial wall thickening and dilatation. The patchy opacities are more common in the periphery of the lung, often in the lower lung zone. HRCT may show much more extensive disease than is expected from review of the chest x-ray.
Pulmonary function tests usually show a restrictive defect, although an obstructive defect (ratio of forced expiratory volume in 1 sec to forced vital capacity [FEV 1 /FVC] < 70%) is found in 21% of patients, and pulmonary function is occasionally normal.
Routine laboratory test results are nonspecific. Leukocytosis without an increase in eosinophils occurs in about one half of patients. The initial ESR often is elevated.
Lung biopsy shows excessive proliferation of granulation tissue within small airways and alveolar ducts, with chronic inflammation in the surrounding alveoli. Foci of organizing pneumonia are nonspecific and can occur secondary to other pathologic processes, including infections, vasculitis, lymphoma, and other interstitial lung diseases such as idiopathic pulmonary fibrosis, nonspecific interstitial pneumonia, connective tissue-related interstitial lung disease, drug induced pulmonary disease, hypersensitivity pneumonitis, and eosinophilic pneumonia.
Clinical recovery follows treatment with corticosteroids in most patients, often within 2 wk. COP recurs occur in up to 50% of patients. Recurrences appear related to the duration of treatment, so treatment should usually be given for 6 to 12 mo. Recurrent disease is generally responsive to additional courses of corticosteroids. Recovery after treatment is common when COP appears on HRCT as parenchymal consolidation, ground-glass opacity, or nodules. In contrast, recovery is less common when COP appears on HRCT as linear and reticular opacities.
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