The human evidence: parenchymal and pleural changes

Our plain-English summary of The human evidence: parenchymal and pleural changes, by G. Hillerdal (The Annals of Occupational Hygiene, 1994).

The study

• Author: G. Hillerdal
• Journal: The Annals of Occupational Hygiene
• Published: 1994;38(4):561-7, 417
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

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.

In plain English

This paper, read at a 1993 workshop on health risks of chrysotile asbestos, was a narrative review of asbestos-caused scarring of the lung (asbestosis) and of the pleura (pleural plaques) as seen on chest X-rays. It presented no new data. The author argued that asbestosis depends strongly on dose, while plaques depend less on dose and appear about 20 to 30 years after exposure. The author noted that only 10-15% of plaques are seen on conventional X-rays. When 'possible' plaques are included, half or more of X-ray-diagnosed plaques are not confirmed at autopsy. Smoking can also produce opacities resembling mild fibrosis. Radiological plaque frequency in the large chrysotile mines of Canada was described as about 2-10%. The author questioned the view that asbestos raises lung cancer risk only when asbestosis is present. In support, the author cited the author's own separate prospective study, which reported a relative risk of 1.4 for lung carcinoma in people with plaques but without asbestosis. The author concluded that strict radiological criteria are essential and that following up people with plaques offers only limited medical gains.

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: Narrative review (workshop paper); no original data presented
• Who was studied: No study population of its own; the paper discussed published reports on asbestos-exposed workers (miners, shipyard and insulation workers, other occupations) and the general population
• Exposure: Asbestos in general, occupational and environmental; the author notes that more than 90% of asbestos used has been chrysotile
• Main results:
  • The author stated that asbestosis is strongly dose-related, whereas for pleural plaques dose is less important and latency is around 20-30 years regardless of exposure
  • The author stated that only 10-15% of plaques are seen with conventional radiography
  • The author stated that when 'possible' or 'suspect' plaques are included, half or more of radiologically diagnosed plaques are not confirmed at autopsy
  • The author stated that smoking alone can cause small irregular opacities indistinguishable from low-grade fibrosis
  • The author described the frequency of radiological pleural plaques in the large chrysotile mines of Canada as about 2-10%
  • Citing the author's own separate 1994 prospective study, the paper reported a relative risk of 1.4 for lung carcinoma in persons with pleural plaques but without asbestosis (no confidence interval given)
• The authors' conclusion: The authors concluded that strict radiological criteria are essential, and that whether to follow up carriers of pleural plaques is an economic and political question from which only limited medical gains are expected
• Limitations the authors state:
  • Diffuse pleural thickening and exudative pleurisy were not analysed in this review

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Chrysotile.

Medical terms in this study, explained in our Lexicon: Parenchyma, Pleura, Pleural Plaques, Dose-response relationship, Carcinoma, Lung Cancer, Mesothelioma.

Related studies

• Pleural and parenchymal fibrosis mainly affecting the upper lung lobes in persons exposed to asbestos — G. Hillerdal (1990)
• Biopersistence of refractory ceramic fiber in human lung tissue and a 20-year follow-up of radiographic pleural changes in workers — J.E. Lockey, V.L. Roggli, et al. (2012)
• Radiographic changes in a group of chrysotile miners and millers exposed to low asbestos dust concentrations — S. Cordier, G. Theriault, et al. (1984)
• Human evidence: lung cancer mortality risk from chrysotile exposure — J.M. Hughes (1994)
• Radiological changes in asbestos cement workers — K. Jakobsson, U. Strömberg, et al. (1995)
• A systematic review of the association between pleural plaques and changes in lung function — L. Kopylev, K.Y. Christensen, et al. (2015)

Browse more research in The Annals of Occupational Hygiene, or return to medical research.