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Idiopathic interstitial pneumonias: the role of environmental triggers.

Idiopathic--or cryptogenic--fibrosing alveolitis is defined by a cluster of clinical, radiological, functional, and pathological features as well as by the exclusion of a recognized "cause.'' The processes by which clinicians assign causes to nonspecific diseases are complex and often subjective. Furthermore, the disease is comparatively rare and is generally diagnosed only after the use of specialized techniques. As a result, the study of its etiological factors is difficult and has been largely unrewarding. The distribution of the disease, so far as it is understood, favors the elderly and, to a lesser extent, males. In some countries mortality has been rising, although it is not clear whether this can be attributed to a diagnostic shift. Studies of occupational classifications among patients dying with the disease offer no striking etiological leads. Four potential etiologies have been formally studied: occupational dust exposures, cigarette smoking, prescription drug use, and viral infections. Three studies have indicated a role for wood and metal dust exposures; methodological issues, however, leave room for remaining doubt and these studies require verification in other populations. There is little epidemiological evidence that cigarette smoking contributes to the disease, or that therapeutic drug use plays an important part. The role of viral infections, particularly those related to Epstein-Barr virus (EBV), is intriguing but remains largely unsubstantiated.