Pleural plaque

Involvement of the pleura, i.e. formation of pleural plaques (fibrotic masses on the pleura) may accompany asbestosis or occur independently, that is, as lesions with no obvious causal relationship (Whitwell, 1978). Pleural plaques only occasionally cause symptoms, as when they restrict the motion of the lung by thickening the membrane (pleura) around the lung or disrupting tissue viability by calcifying. 

Another and also quite common observation is the occurrence of pleural plaques. When it is bilateral, the occurrence has been cited as evidence of... 

Hillerdal, G. (1980). Pleural plaques occurrence, exposure to asbestos and clinical implications. Acta Universitatis Upsceliensis 363 1-277. 

Toxicology. Asbestos causes chronic fibrotic lung disease (asbestosis), pleural plaques and thickening, and cancers of the lungs, pleura, and peritoneum. 

Effects on breathing from pleural plaques alone are usually not serious. There is conflicting evidence as to whether their presence in a person accurately predicts more serious disease development in the future. 

Another tissue that may be affected in humans exposed to asbestos in air is the pleura. The most common effect is the formation of thickened fibrous areas called plaques, but diffuse thickening and fibrosis may also occur, as may areas of pleural effusions. An increased incidence of pleural plaques has been noted at relatively low cumulative exposures (approximately 0.12 f-5T/mL). Localized pleural plaques are not thought to be of significant health concern, although diffuse pleural thickening and circumscribed pleural plaques are associated with impairment of respiratory function. This may also be due to subclinical alveolitis or interstitial fibrosis not detected by routine chest radiograms. These plaques are normally very mild, but may be severe in a few cases probably associated with high exposures. 

Overview of Health Effects. Studies in humans and animals indicate that inhalation of asbestos fibers may lead to fibrotic lung disease (asbestosis), pleural plaques and thickening, and cancer of the lung, the pleura, and the peritoneum. It may also increase the risk of cancer at other sites, but the evidence is not strong. Significant effects on other tissues have not been detected. A number of researchers have found that the occurrence of asbestosis and lung cancer correlates with cumulative exposure (that is, the product of concentration [PCM fibers/mL] multiplied by years of exposure). Therefore, human exposures are expressed below as PCM f-yr/mL. Animal data are provided in terms of exposure level (PCM f/mL) and duration, and the cumulative exposure can be found simply by calculating the product. However, due to differences in clearance rates and lifespan as well as other differences, cumulative doses in animals are not expected to be directly comparable to cumulative doses in humans. Studies that provide reliable dose-... 

As discussed in Section 3.2 and Chapter 2, numerous studies of occupationally-exposed adult workers identify respiratory effects including interstitial fibrosis, lung cancer, and pleural and/or peritoneal mesotheliomas, as critical health effects, of concern from exposure to airborne asbestos. T ically, these health effects follow chronic exposures and exhibit latencies of 10-40 years, although some cases of asbestosis and pleural plaques have been reported following subchronic exposure. 

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