Cryptogenic organizing pneumonia (COP), a form of idiopathic interstitial pneumonia, 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 an illness that resembled community-acquired pneumonia (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 of cryptogenic organizing pneumonia 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. 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 dilation. 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 second to forced vital capacity [FEV1/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 erythrocyte sedimentation rate (ESR) often is elevated.
Lung biopsy (surgical or bronchoscopic) 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 chronic eosinophilic pneumonia.
Clinical recovery follows treatment of cryptogenic organizing pneumonia with corticosteroids in most patients, often within 2 weeks.
Cryptogenic organizing pneumonia 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 months. 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.