Morphology of small-airway lesions in patients with asbestos exposure.

The morphologic changes in the small airways of 15 patients who had been exposed to asbestos and had abnormalities of the respiratory bronchioles and alveolar ducts were examined and compared with changes in the small airways of a matched group of cigarette smokers. Lesions were evaluated using a visual grading scheme to determine pathologic severity of fibrosis, inflammation, and pigmentation in these airways. The membranous bronchioles of both asbestos-exposed and cigarette exposed patients showed the deposition of fibrous tissue and pigment; the lesions were morphologically identical, although more severe in the asbestos group (67 per cent of airways) than in the smoking group (19 per cent of airways). A distinctive lesion, consisting of fibrosis often accompanied by pigment, was found in 74 per cent of the respiratory bronchioles in the asbestos-exposed patients, compared with 6 per cent of respiratory bronchioles in the smokers. Similar changes were found in 49 per cent of alveolar ducts in the asbestos group and 1 per cent of the ducts in smoking group. Asbestos bodies were found in only 11 of 15 cases. The authors conclude that a distinctive lesion of small airways exists in some asbestos workers and that it can be identified by the finding of marked fibrosis in the walls of respiratory bronchioles and alveolar ducts. Because there is no proof that this lesion actually progresses to interstitial fibrosis (asbestosis), the authors suggest that it be termed "asbestos airways disease."