Seminars in respiratory infections
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Bronchiolitis obliterans organizing pneumonia (BOOP) is increasingly recognized as an important cause of diffuse infiltrative lung disease. It is a diagnostic consideration in patients with a febrile flu-like illness of a few weeks' duration and a roentgenogram showing bilateral patchy infiltrates that are not responsive to a typical course of antibiotics. It is defined as granulated tissue plugs within lumens of small airways that extend into alveolar ducts and alveoli. ⋯ This type of therapy is often effective in patients with associated systemic disorders or in other clinical settings, but there may be limited or no response in patients with dermatomyositis, immunosuppression, or interstitial opacities at the lung bases. Respiratory failure leading to death may occur in 5% of patients. It is important to add BOOP to the differential diagnosis of febrile, noninfectious illnesses that are mimics of pneumonia.
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Hypersensitivity pneumonitis or extrinsic allergic alveolitis is an immunologically mediated lung disease caused by repeated inhalations of organic antigens. The basic histological lesion consists of a diffuse mononuclear cell infiltration of alveolar wall, alveoli, terminal bronchioles, and neighboring interstitium. The inflammation is often followed by granulomas, which then may progress to fibrosis. ⋯ Once the diagnosis is suspected, the presence of serum precipitating antibodies (immunoglobulin [lg] G), suppressor cytotoxic lymphocytosis in bronchoalveolar lavage (BAL) fluid, and granulomatous alveolitis in lung biopsy specimens is extremely helpful in confirming the diagnosis. For patients in whom the diagnosis is confirmed, avoidance of the causative antigen is the best therapy, although corticosteroids are used to suppress inflammation. Once the fibrosis has developed, the patient may gradually develop respiratory failure or cor pulmonale, possibly resulting in death.