Cryptogenic organizing pneumonia, a form of idiopathic interstitial pneumonia Overview of Idiopathic Interstitial Pneumonias Idiopathic interstitial pneumonias (IIPs) are interstitial lung diseases of unknown etiology that share similar clinical and radiologic features and are distinguished primarily by the histopathologic... read more , 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 Community-Acquired Pneumonia Community-acquired pneumonia is defined as pneumonia that is acquired outside the hospital. The most commonly identified pathogens are Streptococcus pneumoniae, Haemophilus influenzae... read more 
(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
High-resolution CT (HRCT)
Sometimes lung biopsy
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 Chronic Eosinophilic Pneumonia Chronic eosinophilic pneumonia (CEP) is a disorder of unknown etiology characterized by an abnormal, chronic accumulation of eosinophils in the lung. (See also Overview of Eosinophilic Pulmonary... read more 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 Overview of Tests of Pulmonary Function Pulmonary function tests provide measures of airflow, lung volumes, gas exchange, response to bronchodilators, and respiratory muscle function. Basic pulmonary function tests available in the... read more 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 Overview of Lymphoma Lymphomas are a heterogeneous group of tumors arising in the reticuloendothelial and lymphatic systems. The major types are Hodgkin lymphoma Non-Hodgkin lymphoma See table Comparison of Hodgkin... read more , and other interstitial lung diseases such as idiopathic pulmonary fibrosis Idiopathic Pulmonary Fibrosis Idiopathic pulmonary fibrosis (IPF), the most common form of idiopathic interstitial pneumonia, causes progressive pulmonary fibrosis. Symptoms and signs develop over months to years and include... read more 
, nonspecific interstitial pneumonia Nonspecific Interstitial Pneumonia Nonspecific interstitial pneumonia is an idiopathic interstitial pneumonia that occurs mainly in women, nonsmokers, and patients < 50 years. Patients have cough and dyspnea, which may be... read more 
, connective tissue-related interstitial lung disease, drug-induced pulmonary disease Drug-Induced Pulmonary Disease Drug-induced pulmonary disease is not a single disorder, but rather a common clinical problem in which a patient without previous pulmonary disease develops respiratory symptoms, chest x-ray... read more , hypersensitivity pneumonitis Hypersensitivity Pneumonitis Hypersensitivity pneumonitis is a syndrome of cough, dyspnea, and fatigue caused by sensitization and subsequent hypersensitivity to environmental (frequently occupational or domestic) antigens... read more 
, and chronic eosinophilic pneumonia Chronic Eosinophilic Pneumonia Chronic eosinophilic pneumonia (CEP) is a disorder of unknown etiology characterized by an abnormal, chronic accumulation of eosinophils in the lung. (See also Overview of Eosinophilic Pulmonary... read more .
Treatment of Cryptogenic Organizing Pneumonia
Corticosteroids
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 cryptogenic organizing pneumonia appears on HRCT as parenchymal consolidation, ground-glass opacity, or nodules. In contrast, recovery is less common when cryptogenic organizing pneumonia appears on HRCT as linear and reticular opacities.
