The interstitial lung diseases are a group of chronic disorders that involve the entire lung parenchyma as well as the alveolar interstitium. Although fibrosis of the alveolar interstitium is a process common to all, the interstitial lung diseases are also distinguished by the presence of a chronic alveolitis that produces a derangement of the alveolar structures and ultimately leads to loss of functional gas exchange units ("end stage lung"). Studies of the cellular constituents of the alveolitis obtained by bronchoalveolar lavage strongly suggest that they may be categorized on the basis of the cell type relevant to the pathologic process involved. The central pathogenetic mechanisms operative in these diseases are those that relate to a maintenance of this alveolitis. The alveolitis in these disorders appears to be maintained by the local production of specific cell-derived chemotactic factors that recruit inflammatory cells from the blood into the alveolar interstitium with resultant disordering of the lung's connective tissue skeleton ("fibrosis") and injury of the parenchymal cell populations. Although examination of tissue obtained by open lung biopsy provides a definitive means of assessing the alveolitis, this approach cannot be employed serially during the course of the disease. However, recovery of alveolar cells and relevant proteins by bronchoalveolar lavage and 67gallium scintigraphy provide a safe, reliable means to monitor the activity and character of the alveolitis underlying these interstitial lung diseases. Analysis of lavage cells provides an accurate reflection of the inflammatory and immune cells populating the alveolar structure, and can provide the serial information necessary to determine the prognosis and to gauge the effects of therapy. 67Gallium scintigraphy complements lavage cell analysis in that it is sensitive and specific for the alveolitis and may also be employed serially to assess disease activity. Although definitive therapy of the interstitial lung diseases awaits description of the precise etiologic factors involved, corticosteroid and cytotoxic therapy directed at the potentially reversible alveolitis promise more effective clinical control of these diseases when the results can be monitored by bronchoalveolar lavage and 67gallium scanning in conjunction with conventional roentgenographic and physiologic studies.
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