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

Our plain-English summary of Benign and malignant pleural effusions in former Wittenoom crocidolite millers and miners, by W.O. Cookson, N.H. De Klerk, A.W. Musk, et al (Australian and New Zealand Journal of Medicine, 1985).

The study

• Authors: W.O. Cookson, N.H. De Klerk, A.W. Musk, J.J. Glancy, B.K. Armstrong, M.S. Hobbs
• Journal: Australian and New Zealand Journal of Medicine
• Published: 1985;15(6):731-7
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001219).

Abstract

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)

In plain English

The authors reviewed chest X-rays taken between 1943 and 1982 for 280 compensation claimants for asbestosis and 32 for malignant pleural mesothelioma. All had been exposed to crocidolite (blue asbestos) at the Wittenoom mine and mill in Western Australia. Two readers looked for effusion caused by mesothelioma and for benign asbestos pleural effusion: fluid that appeared and cleared within two years, with no other cause found and at least three years of follow-up afterward. Reader 1 found 15 benign effusions and 18 caused by mesothelioma. Reader 2 found 24 and 20. The time from starting work to the effusion was much shorter for benign effusion than for mesothelioma, but the ranges overlapped. The longest time for a benign effusion was 22 years and the shortest for mesothelioma was 12 years (reader 2). A longer time and work in the mill were associated with mesothelioma as the cause. Asbestosis claimants with a benign effusion were more likely to have more severe diffuse pleural thickening later. The authors noted that the overlap limits diagnostic use and that selecting subjects by compensation claim limits their conclusions.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Review of serial plain chest radiographs of compensation claimants, read separately by two observers, with regression analyses of latent period. Benign asbestos pleural effusion (BAPE) was not diagnosed if follow-up after the effusion resolved was less than three years.
• Who was studied: Former Wittenoom (Western Australia) asbestos workers who claimed compensation: radiographs were retrieved for 280 asbestosis claimants and 32 malignant pleural mesothelioma claimants
• Exposure: Crocidolite (blue asbestos) at the Wittenoom mine and mill, which operated from 1943 to 1966. Cumulative exposure in fibres per cc-years was estimated from employment history and 1966 fibre counts.
• Main results:
  • Reader 1 found 15 cases of BAPE, 18 effusions due to malignant pleural mesothelioma (MPME) and four due to other causes. Reader 2 found 24 BAPE, 20 MPME and eight other effusions.
  • Agreement between readers (Cohen's kappa) was 0.69 for benign effusion and 0.89 for malignant effusion.
  • The latent period from starting work to the first radiograph showing effusion was much shorter for BAPE than for MPME, with considerable overlap. The longest BAPE latent period was 22 years (reader 2; 20 for reader 1). The shortest MPME latent period was 12 years (reader 2; 13 for reader 1).
  • For BAPE (reader 1), only log total exposure was significantly related to latent period: higher exposure went with a shorter latent period (b = -34.75, standard error 9.34, p = 0.001).
  • For MPME, working in the mill was linked to a shorter latent period (b = -67.8, standard error 22.4, p = 0.0007). Total exposure and age at starting work were not related to latent period. Reader 2's results were similar.
  • In logistic regression (reader 1), a longer latent period was associated with MPME rather than BAPE (b = 0.0337, standard error 0.0098, p = 0.001). For mill working, the article printed a standard error of 1.050 and p = 0.06.
  • Among asbestosis claimants, the proportion with a preceding BAPE rose roughly ten-fold from no diffuse pleural thickening to thickening of 1 cm or more. The chi-square for trend was 13.6 (p less than 0.001) for reader 1 and 21.8 (p less than 0.0001) for reader 2.
  • BAPE appeared to resolve rapidly: the median time to the next chest radiograph without effusion was 12 months.
  • Diffuse pleural thickening preceded the effusion in two of the ten MPME cases with prior films seen by reader 1, and in three of the 12 seen by reader 2.
• The authors' conclusion: The authors concluded that two features were significant indicators of a malignant origin for pleural effusion: a long latent period between first exposure to crocidolite and onset of effusion, and a history of working in the mill. They also concluded that the results suggest BAPE is a risk factor for diffuse pleural thickening.
• Limitations the authors state:
  • The substantial overlap between the latent periods of BAPE and MPME limits the value of latent period for diagnosis.
  • Subjects were selected by compensation claim, so the data probably reflect all cases of MPME better than all cases of BAPE.
  • Follow-up of the cohort was cut short: many ex-employees remain alive, and cases of MPM are yet to be diagnosed.
  • There was no organised radiographic surveillance after employment ended, so the latent period to onset of effusion was hard to determine precisely.
  • Total exposure estimates are likely to be conservative.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Crocidolite, Mesothelioma, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Pleural Effusion, Wittenoom, Crocidolite, Chest X-Ray, Pleural Mesothelioma, Diffuse Pleural Thickening, Benign Asbestos Pleural Effusion, Cumulative Exposure.

Related studies

• Prevalence of radiographic asbestosis in crocidolite miners and millers at Wittenoom, Western Australia — W.O. Cookson, N.H. De Klerk, et al. (1986)
• Mortality of former crocidolite (blue asbestos) miners and millers at Wittenoom — A.W. Musk, N.H. de Klerk, et al. (2008)
• Malignant pleural and peritoneal mesotheliomas in former miners and millers of crocidolite at Wittenoom, Western Australia — G. Berry, N.H. de Klerk, et al. (2004)
• Malignant mesotheliomas in former miners and millers of crocidolite at Wittenoom (Western Australia) after more than 50 years follow-up — G. Berry, A. Reid, et al. (2012)
• The natural history of asbestosis in former crocidolite workers of Wittenoom Gorge — W. Cookson, N. De Klerk, et al. (1986)
• Predictions of future cases of asbestos-related disease among former miners and millers of crocidolite in Western Australia — N.H. de Klerk, B.K. Armstrong, et al. (1989)

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