Bronchiolitis obliterans organizing pneumonia

Editor(s)-in-Chief: C. Michael Gibson, M.S., M.D. [mailto:mgibson@perfuse.org] Phone:617-632-7753; Philip Marcus, M.D., M.P.H.[mailto:pmarcus192@aol.com]

Overview
Bronchiolitis obliterans organizing pneumonia (BOOP) is an inflammation of the bronchioles and surrounding tissue in the lungs. BOOP is often caused by a pre-existing chronic inflammatory disease like rheumatoid arthritis. In cases where no cause is found, the disease is called cryptogenic organizing pneumonia.

The clinical features and radiological imaging resemble infectious pneumonia. However, diagnosis is suspected after there is no response to multiple antibiotics, and blood and sputum cultures are negative for organisms.

Symptoms

 * Cough
 * Dyspnea
 * Influenza-like symptoms
 * febrile illness
 * widespread crackles
 * mild resting hypoxemia

On examination, crackles are common, but clubbing is not. Laboratory findings are nonspecific. Plain chest radiography shows normal lung volumes, with characteristic patchy unilateral or bilateral consolidation. Small nodular opacities occur in up to 50% of patients and large nodules in 15%. On HRCT, airspace consolidation with air bronchograms is present in more than 90% of patients, often with a lower zone predominance A subpleural or peribronchiolar distribution is noted in up to 50% of patients. Ground glass or hazy opacities associated with the consolidation are detected in most patients. Pulmonary physiology is restrictive with a reduced DLCO. Airflow limitation is uncommon; gas exchange is usually abnormal and mild hypoxemia is common. Bronchoscopy with BAL reveals up to 40% lymphocytes, along with more subtle increases in neutrophils and eosinophils. In patients with typical clinical and radiographic features, a transbronchial biopsy that shows the pathologic pattern of organizing pneumonia and lacks features of an alternative diagnosis is adequate to make a tentative diagnosis and start therapy. On surgical lung biopsy, the histopathologic pattern is organizing pneumonia with preserved lung architecture; this pattern is not exclusive to BOOP and must be interpreted in the clinical context. Most patients recover with corticosteroid therapy. A standardized approach to dosing starting at 0.75 mg/kg and weaning over 24 weeks has been shown to reduce total corticosteroid exposure without affecting outcome.