Do asbestos-related pleural plaques on HRCT scans cause restrictive impairment in the absence of pulmonary fibrosis?

Our plain-English summary of Do asbestos-related pleural plaques on HRCT scans cause restrictive impairment in the absence of pulmonary fibrosis?, by B. Clin, C. Paris, J. Ameille, et al (Thorax, 2011).

The study

• Authors: B. Clin, C. Paris, J. Ameille, P. Brochard, F. Conso, A. Gislard, F. Laurent, M. Letourneux, A. Luc, E. Schorle, J.C. Pairon
• Journal: Thorax
• Published: 2011;66(11):985-91
• Cited by: 44 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: It is uncertain whether isolated pleural plaques cause functional impairment.

Objective: To analyse the relationship between isolated pleural plaques confirmed by CT scanning and lung function in subjects with occupational exposure to asbestos.

Methods: The study population consisted of 2743 subjects presenting with no parenchymal interstitial abnormalities on the high-resolution CT (HRCT) scan. Asbestos exposure was evaluated by calculation of an individual cumulative exposure index (CEI). Each subject underwent pulmonary function tests (PFTs) and HRCT scanning. Variables were adjusted for age, smoking status, body mass index, CEI to asbestos and the centres in which the pulmonary function tests were conducted.

Results: All functional parameters studied were within normal limits for subjects presenting with isolated pleural plaques and for those presenting with no pleuropulmonary abnormalities. However, isolated parietal and/or diaphragmatic pleural plaques were associated with a significant decrease in total lung capacity (TLC) (98.1% predicted in subjects with pleural plaques vs. 101.2% in subjects free of plaques, p=0.0494), forced vital capacity (FVC) (96.6% vs. 100.4%, p<0.001) and forced expiratory volume in 1 s (FEV(1)) (97.9% vs. 101.9%, p=0.0032). In contrast, no significant relationship was observed between pleural plaques and FEV1/FVC ratio, forced expiratory flow at 25-75% FVC and residual volume. A significant correlation was found between the extent of pleural plaques and the reduction in FVC and TLC, whereas plaque thickness was not related to functional impairment.

Conclusions: The results show a relationship between isolated parietal and/or diaphragmatic pleural plaques and a trend towards a restrictive pattern, although the observed decrease in FVC and TLC is unlikely to be of real clinical relevance for the majority of subjects in this series.

In plain English

This French cross-sectional study asked whether pleural plaques seen on high-resolution CT scans, without scarring of the lung tissue, were linked to reduced lung function. It included 2,743 retired or unemployed volunteers (95.4% men) who had been exposed to asbestos at work, drawn from a surveillance programme in four French regions. Industrial hygienists estimated each person's cumulative asbestos exposure from their job history. People with interstitial abnormalities on CT were excluded. Of the 2,743, 403 had pleural plaques with no other CT abnormality and 1,802 had no abnormality. The analysis adjusted for age, smoking, body mass index, asbestos exposure and testing centre. Compared with the normal-scan group, the plaque-only group had lower total lung capacity (98.1% vs 101.2% of predicted), forced vital capacity (96.6% vs 100.4%) and volume breathed out in one second (97.9% vs 101.9%). All of these values were within normal limits. Larger plaque extent went with lower forced vital capacity and total lung capacity. Plaque thickness did not. The authors concluded this showed a trend towards a restrictive pattern that was unlikely to be clinically relevant for most subjects.

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 study within a medical surveillance programme for people formerly exposed to asbestos at work
• Who was studied: 2,743 retired or unemployed volunteers previously exposed to asbestos at work, from four French regions (Aquitaine, Upper Normandy, Lower Normandy, Rhône-Alpes), in a programme set up in 2001. 95.4% were men and the mean age was 62.9 years. People with interstitial abnormalities on HRCT were excluded. 403 had isolated pleural plaques and 1,802 had no pleuropulmonary abnormalities.
• Exposure: Occupational asbestos exposure (fiber types not specified). Industrial hygienists estimated it from a standardised questionnaire on all jobs held, rating each job on a 4-level scale and multiplying by duration to give a cumulative exposure index in 'exposure units × years'. Mean duration of exposure was 30.7 years.
• Main results:
  • Of 2,743 subjects, 403 (14.7%) had isolated parietal and/or diaphragmatic pleural plaques and 1,802 (65.7%) had no pleuropulmonary abnormalities.
  • After adjustment, subjects with isolated pleural plaques had lower total lung capacity than those with normal CT scans (98.1% vs 101.2% predicted, p = 0.0494). They also had lower forced vital capacity (96.6% vs 100.4%) and FEV1 (97.9% vs 101.9%, p = 0.0032).
  • In the isolated pleural plaque group, no significant relationship was found with the FEV1/FVC ratio, forced expiratory flow at 25 to 75% of FVC, or residual volume.
  • The lung function results were within normal limits. The authors described the changes as modest overall.
  • The share of subjects with total lung capacity below the predicted value was the same (24.1%) in the isolated plaque group and the normal-scan group.
  • The share of subjects with forced vital capacity below the predicted value was higher in the isolated plaque group than in the normal-scan group (9.2% vs 6.0%, p = 0.0222).
  • Among subjects with isolated pleural plaques, total lung capacity and forced vital capacity decreased as the extent of plaques increased.
  • Maximum plaque thickness was not significantly related to any lung function measure analysed.
  • Diffuse pleural thickening (41 subjects) was associated with a significant decrease in all lung function measures compared with subjects with normal scans.
  • Pleural plaques combined with other CT abnormalities (123 subjects) were associated with significant decreases in FVC, FEV1, the FEV1/FVC ratio and FEF25-75.
• The authors' conclusion: The authors concluded that isolated pleural plaques on CT were related to a trend towards a restrictive pattern that increased with plaque extent. They judged the decrease in FVC and TLC unlikely to be of real clinical relevance for most subjects. They also confirmed an association between diffuse pleural thickening and a restrictive pattern.
• Limitations the authors state:
  • Subjects were retired or inactive volunteers, so they do not represent all asbestos-exposed people, some of whom are still working.
  • People already diagnosed with asbestos-related disease, or under surveillance for severe respiratory insufficiency, may not have taken part. This could explain the good lung function results.
  • A healthy worker effect may be present among subjects with extensive exposure.
  • Plaque extent was assessed with a simplified method based on only three reference CT slice levels.
  • The exposure index is semi-quantitative, because there were no air measurements and no detailed information on how often workers were exposed.

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: Pleural Plaques, High-Resolution CT (HRCT), Pulmonary Fibrosis, Occupational Exposure, Interstitial, Asbestos Exposure, Cumulative Exposure, Pulmonary Function Test (PFT).

Related studies

• Does asbestos exposure cause airway obstruction, in the absence of confirmed asbestosis? — J. Ameille, M. Letourneux, et al. (2010)
• Inter-reader agreement in HRCT detection of pleural plaques and asbestosis in participants with previous occupational exposure to asbestos — F. Laurent, C. Paris, et al. (2014)
• Pleural plaques and asbestosis: dose- and time-response relationships based on HRCT data — C. Paris, S. Thierry, et al. (2009)
• Restrictive lung function and asbestos-induced pleural fibrosis. A quantitative approach — D.A. Schwartz, J.R. Galvin, et al. (1993)
• Asbestos-related pleural diseases: dimensional criteria are not appropriate to differentiate diffuse pleural thickening from pleural plaques — J. Ameille, M. Matrat, et al. (2004)
• Pulmonary function, smoking habits, and high resolution computed tomography (HRCT) early abnormalities of lung and pleural fibrosis in shipyard workers exposed to asbestos — S. Neri, P. Boraschi, et al. (1996)

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