Benign and malignant pleural effusions in former Wittenoom crocidolite millers and miners

Serial plain chest radiographs taken between 1943 and 1982 for 280 claimants for compensation for asbestosis and 32 claimants for malignant pleural mesothelioma from the Wittenoom asbestos industry were reviewed by two observers to identify diffuse pleural thickening and pleural effusion. A pleural effusion which appeared and resolved within two years without radiographic or clinical evidence of underlying malignancy, infection or cardiac failure was seen in 15 cases by reader 1 and 24 cases by reader 2. Eighteen cases of effusion, determined from clinical records to be caused by malignant pleural mesothelioma, were seen by reader 1 and 20 by reader 2. The latent periods between commencing work and the first radiograph showing effusion were much shorter for subjects with benign asbestos pleural effusion than for subjects with effusion due to malignant pleural mesothelioma, although there was considerable overlap in the range. The longest latent period for benign asbestos pleural effusion was 22 years and the shortest period for effusion due to malignant pleural mesothelioma was 12 years. The latent period for benign asbestos pleural effusion was inversely related to total cumulative exposure, whereas that for effusion due to malignant pleural mesothelioma was significantly shorter for subjects who had worked in the mill than for those who had worked in the mine. A long latent period and a history of working in the mill were significant discriminators for a malignant as opposed to a benign basis for an effusion. The appearance of a benign asbestos pleural effusion appeared to be a risk factor for the severity of subsequent diffuse pleural thickening.(ABSTRACT TRUNCATED AT 250 WORDS)