Some Observations on the Epidemiology of Benign Pleural Disease

Abstract

The results from radiographic and respiratory function surveys in Quebec chrysotile miners and millers, Montana vermiculite workers and villagers from the Metsovo region of north-west Greece are compared. Large differ ences are seen in the prevalence and extent of pleural calcification, diffuse pleural thickening and small parenchymal opacities, with confirmatory evi dence from pulmonary function and respiratory symptoms. These findings together with analyses of mortality point to fibrous tremolite as the main cause of mesothelioma and excess lung cancer in these populations and, with chryso tile in the Quebec workers, of pulmonary and pleural fibrosis. Were fibrous tremolite also to have been the cause of the extremely high rates of extensive pleural calcification in the Greek villages, this would surely have been accom panied by high levels of pulmonary fibrosis, lung cancer and mesothelioma. The first was certainly lacking, and indications of excess malignant disease quite uncertain. It is suggested that some, as yet unidentified, agent such as non-fibrous tremolite, often closely associated geologically with asbestiform fibre deposits, may be responsible for calcified pleural plaques.