NORD gratefully acknowledges O'Neil Green, MD, Critical Care Medicine and Pulmonology, Baystate Wing Hospital, for assistance in the preparation of this report.
Bronchiolitis obliterans organizing pneumonia (BOOP) is a rare inflammatory lung disorder which was first described in the 1980’s as a unique disease entity composed of clinical symptoms such as flu-like illness in many individuals as well as cough and shortness of breath with exertional activities. Wheezing and hemoptysis are rare. The term bronchiolitis obliterans refers to swirls or plugs of fibrous, granulation tissue filling the small bronchiole airways. Organizing pneumonia refers to organized swirls of inflammatory tissue filling the small spherical units of the lungs referred to as alveoli and the alveolar ducts. Individuals with BOOP experience inflammation of the bronchioles and alveolar lung spherical units simultaneously, which distinguishes it from other similar inflammatory lung disorders. Though the term pneumonia is used, BOOP is not an infection.
Although several different known causes of BOOP have been identified, most cases occur for no known reason (idiopathic). Idiopathic BOOP may also be called cryptogenic organizing pneumonia. Some researchers prefer the use of COP to avoid confusion with other lung disorders with similar names. The term cryptogenic denotes that the cause of the disorder is unknown. Others prefer the term BOOP because it the most recognized term for the disorder, and others refer to it as Epler’s pneumonia.
Symptoms of BOOP vary from person to person depending upon the specific type. For example, people with idiopathic BOOP have a flu-like illness, while people with BOOP associated with an underlying connective-tissue disorder have cough or shortness of breath. Some individuals with BOOP such as focal BOOP may have no apparent symptoms, while others may have severe respiratory distress as in acute, rapidly-progressive BOOP.
Symptoms usually develop slowly over a few weeks or months. The most common symptom is a persistent, nonproductive cough. Some affected individuals develop a flu-like illness characterized by a sore throat, a general feeling of ill health (malaise), weight loss, and fatigue. Eventually, shortness of breath especially from exertional activities may develop. The shortness of breath and cough may become progressively worse.
Individuals with BOOP may develop small crackling or rattling sounds in the lung (crackles or rales) that are apparent upon physical examination. In rare cases affected individuals may experience chest pain, joint pain (arthralgia), night sweats or coughing up blood (hemoptysis).
A rapidly progressive form of BOOP exists that can progress from symptom onset to acute respiratory failure in only a few days. This form of BOOP may be associated with an underlying fibrotic process.
In most cases, the cause of BOOP is unknown and is referred to as idiopathic BOOP. Causes of BOOP include radiation therapy; exposure to certain fumes or chemicals, exposure to birds, post respiratory infections, after organ transplantation; and from more than 35 medications. Systemic disorders associated with BOOP include the connective-tissue diseases, immunological disorders, and inflammatory bowel disease. BOOP has also been seen in association with lung abscess, lung cancer, and lymphoma. Importantly, the BOOP lesion is seen in individuals with idiopathic pulmonary fibrosis, or IPF, and in these situations, the primary lung disease is the IPF and the secondary process is BOOP.
BOOP affects males and females in equal numbers. It develops in individuals between 40-60 years old, but the disorder may affect individuals of any age. BOOP is estimated to account for 5 to 10% of the chronic infiltrative lung disease in the United States. BOOP has been reported throughout the world.
A diagnosis of BOOP may be made based upon a clinical evaluation, a detailed patient history, identification of characteristic findings, and specialized tests such as x-ray studies, especially a high-resolution chest computed tomography or HRCT, pulmonary function studies that includes a diffusing capacity test, and often a lung biopsy for microscopic tissue analysis. Lung biopsy may be via conventional transbronchial biopsy which frequently captures the diagnosis, transbronchial cryobiopsy which is newer and recovers a larger bit of tissue or in selected cases, open lung biopsy. The HRCT scan shows “ground glass” densities that are often triangular in shape with the base of the triangle along the chest wall and the airways can often be seen in the ground-glass opacities.
In some patients, the symptoms of BOOP may resolve without treatment especially the post breast radiation-type. In some mild cases such as individuals without symptoms or who have non-progressive disease, the process can be monitored and treated later if necessary. Most individuals with BOOP require treatment with the anti-inflammatory, corticosteroid medication, usually in the form of prednisone. This therapy often results in dramatic improvement with resolution of symptoms within days or weeks. In some situations, the BOOP may recur as the dose is decreased, but the BOOP will respond to an additional course of treatment.
The rapidly progressive form of BOOP is treated with intravenous corticosteroid medication and sometimes with Cytoxan. Individuals wit. secondary BOOP may improve after treating the underlying condition. Additional treatment is symptomatic and supportive.
For individuals who do not respond to steroid therapy, other agents have been used including cyclophosphamide, erythromycin in the form of azithromycin, and Mycophenolate Mofetil (CellCept). These agents have been beneficial to individuals with BOOP on a case-by-case basis reported in the medical literature (anecdotally). However, research is needed to determine the long-term safety and effectiveness of these potential treatment options for individuals with BOOP.
In rare cases, lung transplantation may be necessary for individuals with BOOP who do not respond to standard treatment options.
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