Systematic review of pleural plaques and lung function

Our plain-English summary of Systematic review of pleural plaques and lung function, by L.E. Kerper, H.N. Lynch, K. Zu, et al (Inhalation Toxicology, 2015).

The study

• Authors: L.E. Kerper, H.N. Lynch, K. Zu, G. Tao, M.J. Utell, J.E. Goodman
• Journal: Inhalation Toxicology
• Published: 2015;27(1):15-44
• Type of article: Systematic review
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Context: US EPA proposed a Reference Concentration for Libby amphibole asbestos based on the premise that pleural plaques are adverse and cause lung function deficits.

Objective: We conducted a systematic review to evaluate whether there is an association between pleural plaques and lung function and ascertain whether results were dependent on the method used to identify plaques.

Methods: Using the PubMed database, we identified studies that evaluated pleural plaques and lung function. We assessed each study for quality, then integrated evidence and assessed associations based on the Bradford Hill guidelines. We also compared the results of HRCT studies to those of X-ray studies.

Results: We identified 16 HRCT and 36 X-ray studies. We rated six HRCT and 16 X-ray studies as higher quality based on a risk-of-bias analysis. Half of the higher quality studies reported small but statistically significant mean lung function decrements associated with plaques. None of the differences were clinically significant. Many studies had limitations, such as inappropriate controls and/or insufficient adjustment for confounders. There was little consistency in the direction of effect for the most commonly reported measurements. X-ray results were more variable than HRCT results. Pleural plaques were not associated with changes in lung function over time in longitudinal studies.

Conclusion: The weight of evidence indicates that pleural plaques do not impact lung function. Observed associations are most likely due to unidentified abnormalities or other factors.

In plain English

In this systematic review, the authors searched PubMed through May 2014 for studies of pleural plaques and lung function in adults. The 52 included studies (16 using high-resolution CT, or HRCT, and 36 chest X-ray) either compared people with plaques alone against a reference group or used regression analyses adjusting for other abnormalities. They rated six HRCT and 16 X-ray studies as higher quality. Three of the six higher quality HRCT studies reported statistically significant but very small (3–7%) average lung function decreases; three did not. Seven of 14 higher quality X-ray studies reporting spirometry found statistically significant differences, and X-ray results varied more than HRCT results. Three of four higher quality X-ray studies that classified individuals reported significantly more restriction among people with plaques. None of six longitudinal studies found a significantly greater loss of lung function over time with plaques. Noting the studies could show only associations, the authors concluded the weight of evidence indicates pleural plaques do not cause lung function decrements and are not adverse. They said they could not overcome the individual studies' limitations.

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: Systematic review with study-quality (risk-of-bias) rating and a weight-of-evidence evaluation using the Bradford Hill guidelines. No meta-analysis was done.
• Who was studied: Fifty-two published observational studies of adults, found in PubMed through May 2014: 16 HRCT studies (31 to 2743 participants) and 36 X-ray studies (23 to 6476 participants). Included studies either had subjects with pleural plaques alone (no other abnormalities) compared with a reference group, or used a regression analysis for pleural plaques that adjusted for other abnormalities.
• Exposure: Pleural plaques, identified by HRCT or X-ray, in populations exposed to different types of asbestos, including Libby amphibole asbestos. The outcome was lung function tests.
• Main results:
  • 52 studies were included: 16 HRCT and 36 X-ray. Of these, 6 HRCT and 16 X-ray studies were rated higher quality.
  • Higher quality HRCT studies: 3 of 6 reported statistically significant but very small (3–7%) mean decrements; 3 did not.
  • X-ray studies: 17 of 33 reporting spirometry found a statistically significant decrement in one or more measures in people with pleural plaques. Among 14 higher quality X-ray studies, 7 reported statistically significant differences.
  • Higher quality X-ray studies that classified individual participants: 3 of 4 reported a significant increase in restriction among people with pleural plaques, and 1 reported an increase in mixed restriction/obstruction.
  • The range of lung function differences was much smaller in HRCT studies than in X-ray studies. The authors took this to mean X-ray studies are less reliable for this question.
  • Six longitudinal studies (2 HRCT, 4 X-ray; follow-up 2 to 10 years): none showed a significantly greater loss of lung function over time in people with pleural plaques than in people with normal scans.
  • Extent of plaques: 5 of 6 HRCT studies found no significant effect of plaque number or size on lung function. One HRCT study (Clin et al., 2011) reported significant associations of plaque circumference with FVC and TLC. Among X-ray studies, three showed no effect and three reported associations.
• The authors' conclusion: The authors concluded that the weight of evidence indicates pleural plaques do not cause lung function decrements and are not adverse. They said reported decrements are more likely due to other factors, while noting that the reviewed studies can only evaluate statistical associations.
• Limitations the authors state:
  • The review could not overcome the limitations of the individual studies. Of most concern, the studies did not give lung function results for each individual.
  • For studies that reported only p values, the direction of effect could not be determined, so the analysis may have been biased in either direction.
  • A meta-analysis was considered inappropriate because the studies were highly heterogeneous and showed reporting bias and possible publication bias.
  • Residual confounding by asbestos exposure, smoking and BMI may have affected the reviewed studies, even those that adjusted for these factors.

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: Systematic Review, Pleural Plaques, Libby amphiboles, High-Resolution CT (HRCT).

Related studies

• Comment on "A systematic review of the association between pleural plaques and changes in lung function" by Kopylev et al (2014) — J.E. Goodman, L.E. Kerper, et al. (2015)
• A systematic review of the association between pleural plaques and changes in lung function — L. Kopylev, K.Y. Christensen, et al. (2015)
• Authors' response: A systematic review of the association between pleural plaques and changes in lung function — L. Kopylev, K.Y. Christensen, et al. (2015)
• Pleural plaques and lung function in the Marysville worker cohort: a re-analysis — K. Zu, G. Tao, et al. (2016)
• Abnormal pulmonary function associated with diaphragmatic pleural plaques due to exposure to asbestos — K.H. Kilburn, R.H. Warshaw (1990)
• Pleural plaques and respiratory function — B. Järvholm, A. Sandén (1986)

Browse more research in Inhalation Toxicology, or return to medical research.