Development, radiological zone patterns, and importance of diffuse pleural thickening in relation to occupational exposure to asbestos

Our plain-English summary of Development, radiological zone patterns, and importance of diffuse pleural thickening in relation to occupational exposure to asbestos, by H. Bohlig, A. Calavrezos (British Journal of Industrial Medicine, 1987).

The study

• Authors: H. Bohlig, A. Calavrezos
• Journal: British Journal of Industrial Medicine
• Published: 1987;44(10):673-81
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000345).

Abstract

The radiographic appearance of the lateral pleura was divided into an upper, a middle, and a lower zone. Bilateral changes of the pulmonary layer of the pleura (diffuse pleural thickening) within the upper pleural zones were found in 863 (71%) of 1204 workers exposed to asbestos and in 249 (40%) of 622 non-exposed controls. Downwards along the chest wall this ratio of 7:4 increased progressively up to 10:1 at the lower parts of the pleura. Bilateral diffuse pleural thickening in at least two adjacent zones on each side was found in 652 (54%) of exposed and in only 86 (14%) of unexposed subjects. The difference was even more striking when comparing bilateral involvement of all three zones (28% and 3% respectively). Unilateral change was rare (4.8% and 7.8% respectively) and often due to causes other than exposure to asbestos. Pleural findings were the earliest radiographic features detectable associated with former exposure to asbestos. Bilateral diffuse thickening in at least two adjacent zones on each side seems to be a striking feature and an early indication of former occupational asbestos damage. Modifications of the International Labour Organisation 1980 classification are proposed.

In plain English

In this retrospective, non-blind study, the authors compared chest X-rays of 1204 workers in Germany, examined in 1982, who had at least one year of occupational exposure to asbestos in the asbestos processing and handling industry, including construction, with X-rays of 622 controls with no known occupational exposure to asbestos. One reader, who was not blinded to exposure, reread all films and recorded diffuse pleural thickening by upper, middle and lower chest zones. Bilateral upper-zone thickening was found in 863 (71%) exposed workers and 249 (40%) controls. Bilateral thickening in at least two adjacent zones on each side was found in 652 (54%) exposed workers and 86 (14%) controls, and in all three zones in 28% and 3%. Unilateral thickening was rare in both groups. In exposed workers, bilateral lower-zone thickening appeared later than thickening of the upper or middle zones, in median 10 years later. The authors concluded that diffuse pleural thickening separates exposed from unexposed groups statistically but not individuals. They identified bilateral involvement of at least two adjacent zones as the main distinguishing feature and proposed changes to the ILO 1980 classification. They noted that data on occupational conditions were vague.

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: Retrospective, non-blind comparison of chest radiographs of asbestos-exposed workers with those of unexposed controls
• Who was studied: Group A: 1204 workers in the Federal Republic of Germany (1093 men, 111 women) undergoing medical examination in 1982, each with at least one year of occupational asbestos exposure. Group B: 622 controls with no known occupational exposure to asbestos. Of these, 202 were first films of workers entering the asbestos industry, and 420 were radiographs randomly selected from the archives of two community hospitals (Hamburg and Luedenscheid).
• Exposure: Nearly all types of asbestos dust in the German asbestos processing and handling industry, including construction industries. There were no shipyard workers. Working conditions, duration and dust concentrations could not be assessed.
• Main results:
  • Bilateral diffuse pleural thickening in the upper zones was found in 863 (71%) of 1204 exposed workers and in 249 (40%) of 622 non-exposed controls. One quarter of controls had isolated bilateral upper-zone involvement.
  • Bilateral thickening in at least two adjacent zones on each side was found in 652 (54%) of exposed workers and 86 (14%) of unexposed controls.
  • Bilateral involvement of all three zones was found in 28% of exposed workers and 3% of controls.
  • The ratio of exposed (group A) to control (group B) prevalence was roughly 7:4 for the upper zones and 10:1 for the lower zones.
  • Unilateral pleural thickening was rare: 58 of 1204 exposed workers and 49 of 622 controls, a difference that was not significant. It was often associated with other causes such as trauma.
  • Pleural plaques (215 exposed vs 4 controls) and small opacities of profusion 1/0 or more (167 exposed vs 7 controls) differed significantly between groups (p less than 0.001).
  • After 25 years since first exposure, exposed workers had an estimated 50% risk of bilateral thickening involving all three zones (upper, middle and lower).
  • In exposed workers, bilateral lower-zone thickening developed later than thickening in other zones, in median 10 years later.
  • The figure 2 legend states that, in exposed workers, lower-zone thickening appeared in median between 7 and 12 years later than thickening of the upper or middle zones.
  • In exposed workers, the risk of bilateral pleural thickening increased with older age at first exposure, including after adjustment for time since first exposure.
  • In the exposed group, every case with lung (parenchymal) involvement also had diffuse pleural thickening.
• The authors' conclusion: The authors concluded that diffuse pleural thickening distinguishes exposed from unexposed populations statistically but not individuals, and that bilateral involvement of at least two adjacent zones is the main distinguishing feature. They proposed modifying the ILO 1980 classification to record pleural thickening by zones.
• Limitations the authors state:
  • The reader was not blind to asbestos exposure, so the authors say bias cannot be excluded with certainty.
  • The authors list no blind reading, a limited number of controls, and vague data on occupational conditions, in addition to the retrospective design.
  • Working conditions, duration of exposure and dust concentrations could not be assessed.
  • Because of the retrospective design, the films varied in quality, exposure time and positioning.
  • No time measure comparable to time since first exposure was available for controls, so age at examination was used as a substitute.

Topics

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

Medical terms in this study, explained in our Lexicon: Diffuse Pleural Thickening, Occupational Exposure, Pleura, Bilateral.

Related studies

• A retrospective study on radiological findings of diffuse pleural thickening with benign asbestos pleural effusion in Japanese cases — T. Kishimoto, K. Kato, et al. (2022)
• Development of radiological and clinical evidence of parenchymal fibrosis in men with non-malignant asbestos-related pleural lesions — G.H. McMillan, C.E. Rossiter (1982)
• Radiological features of diffuse mesothelioma — A. Solomon (1970)
• The presentation and natural history of asbestos-induced diffuse pleural thickening — V. Jeebun, S.C. Stenton (2012)
• Asbestos-related diffuse pleural thickening — N. Fujimoto, K. Kato, et al. (2014)
• US prevalence of occupational pleural thickening. A look at chest X-rays from the first National Health and Nutrition Examination Survey — W.J. Rogan, B.C. Gladen, et al. (1987)

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