Asbestosis, pleural plaques and diffuse pleural thickening: three distinct benign responses to asbestos exposure

Our plain-English summary of Asbestosis, pleural plaques and diffuse pleural thickening: three distinct benign responses to asbestos exposure, by P.A. Gevenois, V. de Maertelaer, A. Madani, et al (The European Respiratory Journal, 1998).

The study

• Authors: P.A. Gevenois, V. de Maertelaer, A. Madani, C. Winant, G. Sergent, P. De Vuyst
• Journal: The European Respiratory Journal
• Published: 1998;11(5):1021-7
• Cited by: 94 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The aim of this study was to investigate by computed tomography (CT) whether asbestosis, diffuse pleural thickening and/or pleural plaques are statistically associated. We also tried to find criteria to differentiate between diffuse and circumscribed pleural thickening. From 231 exposed workers, only those subjects whose radiograph showed neither bilateral calcified pleural plaques nor small pulmonary opacities higher than 1/1 grade according to the 1980 International Labour Office (ILO) Classification were considered. Scans were assessed for the presence of subpleural curvilinear lines, septal and intralobular lines, parenchymal bands, honeycombing, rounded atelectasis, pleural plaques and diffuse pleural thickening. CT scans revealed pleural and/or lung abnormalities in 99 workers. Pleural plaques were unilateral in one-third of cases with plaques. Diffuse pleural thickening, parenchymal bands and rounded atelectasis were unilateral in, respectively, 62 and 69 and 75% of cases with the abnormality. Septal and intralobular lines, and honeycombing were always bilateral. CT signs could be grouped into three patterns: 1) septal and intralobular lines, and honeycombing corresponding to pulmonary fibrosis; 2) pleural plaques corresponding to parietal pleural fibrosis; and 3) diffuse pleural thickening, rounded atelectasis and parenchymal bands corresponding to visceral pleural fibrosis. In these workers with a normal or near-normal radiograph, three groups of subjects with different responses were distinguished. Crow's feet and rounded atelectasis help to differentiate plaques from diffuse thickening.

In plain English

This Belgian study used computed tomography (CT) to test whether asbestosis (lung fibrosis), pleural plaques and diffuse pleural thickening tend to occur together. It included 231 asbestos-exposed workers (227 men, 4 women) seeking compensation for pneumoconiosis from the Belgian Occupational Diseases Fund, whose chest X-rays were normal or near-normal. CT showed no abnormality in 132 (57%), and the other 99 were analysed. Pleural plaques, seen in 72, were on both sides in 46 (64%). Lung fibrosis signs were always on both sides. Diffuse pleural thickening, parenchymal bands and rounded atelectasis were one-sided in 62%, 69% and 75% of affected workers. For diffuse thickening and rounded atelectasis, this one-sidedness was not statistically significant. A statistical grouping method sorted the signs into three clusters: lung fibrosis, plaques, and diffuse thickening with bands and rounded atelectasis. Plaques alone occurred in 42 workers. Another 27 had plaques and the diffuse-thickening cluster without lung-fibrosis signs, and 1 had all three clusters. The authors concluded these were three distinct benign responses. They noted that including workers with more advanced X-ray findings might not have produced these clusters.

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: Cross-sectional CT study of referred asbestos-exposed workers. Each CT sign was coded by side, tested with a binomial test for being one-sided versus two-sided, and grouped by cluster analysis.
• Who was studied: 231 workers (227 males, 4 females), aged 30 to 72, seeking compensation for pneumoconiosis at the Belgian Occupational Diseases Fund. Their CT scans were requested over a 4-year period. All had at least 10 years since first exposure and chest radiographs without obvious bilateral calcified pleural plaques or small opacities above ILO grade 1/1. Smoking status: 131 current smokers, 32 ex-smokers, 68 lifetime nonsmokers.
• Exposure: Occupational asbestos exposure confirmed by engineers. Duration ranged from 1 to 48 years (mean 19 years, SD 12), and only 25 workers were exposed for less than 5 years. Fiber types and specific jobs were not reported for these workers.
• Main results:
  • CT detected no abnormality in 132 (57%) of the 231 workers, leaving 99 workers with at least one sign for analysis.
  • Among the 72 workers with pleural plaques, plaques were bilateral in 46 (64%) and unilateral in 26 (36%).
  • Septal and intralobular (core) lines (11 workers) and honeycombing (6 workers) were bilateral in every case.
  • Some signs were unilateral in the following numbers: diffuse pleural thickening in 20 (62%) of 32 cases, parenchymal bands in 24 (69%) of 35 cases, and rounded atelectasis in 6 (75%) of 8 cases.
  • In the binomial test (Table 1), the difference between one-sided and two-sided occurrence was p=0.216 for diffuse pleural thickening and p=0.289 for rounded atelectasis, both not statistically significant. It was p=0.043 for parenchymal bands and p=0.025 for pleural plaques.
  • When unilateral, parenchymal bands and rounded atelectasis were on the same side as pleural thickening.
  • Curvilinear subpleural lines were found in only one worker, were not associated with any other sign, and were dropped from further analysis.
  • Cluster analysis grouped the signs into three clusters: (1) septal and intralobular lines with honeycombing; (2) diffuse pleural thickening with parenchymal bands and rounded atelectasis; (3) pleural plaques.
  • Of the 99 workers: 7 had cluster 1 only, 18 had cluster 2 only, and 42 had pleural plaques only. 2 had clusters 1 and 2 only, 2 had clusters 1 and 3 only, 27 had clusters 2 and 3 only, and 1 had all three.
• The authors' conclusion: The authors concluded that CT showed three distinct types of benign response to asbestos exposure: parenchymal (lung) fibrosis, parietal pleural fibrosis (pleural plaques), and visceral pleural fibrosis (diffuse pleural thickening, rounded atelectasis and parenchymal bands). They suggested such lesions are initially located on one target organ only. They also stated that the absence of pleural signs should not be considered a clue against a diagnosis of asbestosis, and that crow's feet and rounded atelectasis help distinguish plaques from diffuse thickening.
• Limitations the authors state:
  • Workers with bilateral calcified pleural plaques visible on the chest radiograph were not referred for CT, so a selection bias existed.
  • Workers with radiograph opacity grades above 1/1 were deliberately excluded. A study including them might not have shown the same clusters and three types of response.
  • A pathological study of heavily exposed workers might show diseases occurring together more often.
  • Exposure to ergoline drugs, which can cause pleural changes, was not systematically checked.

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Plaques, Diffuse Pleural Thickening, Asbestos Exposure, Pleural Thickening, Bilateral, Subpleural Curvilinear Line, Honeycombing, Rounded Atelectasis.

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