Bronchiolitis obliterans organizing pneumonia
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Overview of Bronchiolitis Obliterans Organizing Pneumonia (BOOP)
Bronchiolitis obliterans organizing pneumonia (BOOP), also known as organizing pneumonia, is an inflammatory lung disease that affects both the small airways (bronchioles) and the surrounding alveoli. It is considered a parenchymal disorder and is distinct from other bronchiolar diseases due to its simultaneous involvement of terminal bronchioles and alveoli, leading to patchy areas of inflammation and fibrosis 12.
Clinical Presentation and Symptoms of BOOP
Patients with BOOP typically present with a subacute onset of symptoms, including cough, fever, flu-like illness, and shortness of breath (dyspnea). These symptoms often persist for several weeks, usually ranging from 4 to 10 weeks 23568. Additional symptoms such as pleuritic chest pain and hemoptysis (coughing up blood) can also occur, though these are less common . On physical examination, crackles are frequently heard in the lungs 25.
Radiological and Pathological Features
Chest imaging in BOOP commonly reveals bilateral patchy infiltrates, often with a "ground glass" appearance or areas of air-space consolidation. These findings are usually patchy and can be migratory or solitary 234678. Computed tomography (CT) scans provide a more accurate assessment of the distribution and extent of the disease compared to plain radiographs, showing features such as small nodular opacities, irregular linear opacities, and sometimes pleural effusions .
Histologically, BOOP is characterized by polypoid masses of granulation tissue (fibromyxoid connective tissue plugs) within the lumens of small airways, alveolar ducts, and alveoli. The fibrosis is typically uniform in age, indicating a simultaneous onset of repair, and the background lung architecture is preserved 29.
Etiology and Associated Conditions
BOOP is most often idiopathic (cryptogenic), but it can also occur secondary to various causes, including infections (such as viral or mycoplasma pneumonia), connective tissue diseases, certain drugs, bone marrow or lung transplantation, radiation therapy, and immunological disorders 5810. It has also been reported in association with common variable immunodeficiency syndrome (CVID), suggesting an immunologic basis in some cases .
Pulmonary Function and Laboratory Findings
Pulmonary function tests in BOOP usually show a restrictive pattern with decreased vital capacity and impaired diffusing capacity. Obstructive patterns are generally limited to smokers 257. Bronchoalveolar lavage fluid (BALF) often reveals increased lymphocytes, neutrophils, and eosinophils, with a decreased CD4+/CD8+ ratio in many patients 37.
Treatment and Prognosis
Corticosteroid therapy is the mainstay of treatment for BOOP and is effective in achieving complete clinical and physiological recovery in the majority of patients (65–85%) 235678. Some patients may recover spontaneously or after surgical resection of a focal lesion 78. Relapses can occur, especially if corticosteroid therapy is tapered too quickly . The overall prognosis is generally good, with a small percentage of patients experiencing respiratory failure leading to death (about 5%) 358.
Differential Diagnosis
BOOP can be confused with other interstitial lung diseases, particularly idiopathic pulmonary fibrosis, due to overlapping clinical and radiological features. However, the benign course and favorable response to corticosteroids in BOOP make histological distinction important for appropriate management 257.
Conclusion
Bronchiolitis obliterans organizing pneumonia is an important and treatable cause of diffuse infiltrative lung disease. It should be considered in patients with persistent flu-like symptoms, patchy lung infiltrates unresponsive to antibiotics, and characteristic histological findings. Early recognition and corticosteroid therapy usually result in a favorable outcome, although relapses and rare fatalities can occur 23578.
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