Histopathology
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The concept of fibrosis with emphysema is confused by the existence of two very different clinical/pathological scenarios: first, cases in which a diffuse fibrosing interstitial pneumonia, most commonly usual interstitial pneumonia (UIP), occurs in a patient with emphysema. This combination is largely of clinical interest because of its effects on pulmonary function and pulmonary hypertension, but can produce unusual appearances in surgical lung biopsies when the fibrotic areas are wrapped around emphysematous spaces. However, the underlying morphology of emphysema and UIP or other interstitial lung disease remains unchanged. ⋯ These lesions have been called 'respiratory bronchiolitis' (RB), 'respiratory bronchiolitis-interstitial lung disease' (RB-ILD), 'airspace enlargement with fibrosis', 'RB-ILD with fibrosis' and 'clinically occult interstitial fibrosis in smokers', but are probably all the same entity. Such changes are associated only rarely with the physiological or radiological features of an interstitial lung disease. Care should be taken when describing these lesions in biopsies so as not to give the impression that a diffuse interstitial lung disease is present.
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An acute exacerbation is the development of acute lung injury, usually resulting in acute respiratory distress syndrome, in a patient with a pre-existing fibrosing interstitial pneumonia. By definition, acute exacerbations are not caused by infection, heart failure, aspiration or drug reaction. Most patients with acute exacerbations have underlying usual interstitial pneumonia, either idiopathic or in association with a connective tissue disease, but the same process has been reported in patients with fibrotic non-specific interstitial pneumonia, fibrotic hypersensitivity pneumonitis, desquamative interstitial pneumonia and asbestosis. ⋯ Biopsies may be extremely confusing, because the acute injury pattern can completely obscure the underlying disease; a useful clue is that diffuse alveolar damage and organizing pneumonia should not be associated with old dense fibrosis and peripheral honeycomb change. Consultation with radiology can also be extremely helpful, because the fibrosing disease may be evident on old or concurrent computed tomography scans. The aetiology of acute exacerbations is unknown, and the prognosis is poor; however, some patients survive with high-dose steroid therapy.