The human evidence: parenchymal and pleural changes

Asbestos inhalation can cause fibrotic reactions both in the lung parenchyma and in the pleura. The incidence and relative proportions of these lesions in any cohort will be dependent on: (1) the time factor: both asbestosis and pleural plaques are progressive diseases and the longer the time from exposure, the more the changes; (2) the dose-response: the more intense the exposure, the earlier and the more advanced is the asbestosis. However, pleural plaques are only moderately dependent on the exposure level and will occur after approximately 30 years in most persons who develop them, even after fairly low exposure; (3) the early lesions are difficult to diagnose radiologically and are prone to overdiagnosis. Considerable caution is necessary when evaluating results if only such lesions are reported. It is generally accepted that the occurrence of radiological asbestosis is a risk factor, particularly for bronchial carcinoma. However, pleural plaques have been considered to be relatively harmless. Recent data have indicated, however, that they can be indicators of sufficient exposure to increase the risk of other asbestos-related diseases, including lung cancer and mesothelioma.