Pleural plaques and lung function in the Marysville worker cohort: a re-analysis

Our plain-English summary of Pleural plaques and lung function in the Marysville worker cohort: a re-analysis, by K. Zu, G. Tao, J.E. Goodman (Inhalation Toxicology, 2016).

The study

• Authors: K. Zu, G. Tao, J.E. Goodman
• Journal: Inhalation Toxicology
• Published: 2016;28(11):514-9
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: In the 2014 Integrated Risk Information System (IRIS) assessment for Libby amphibole asbestos (LAA), US EPA calculated a reference concentration (RfC) based on the prevalence of pleural plaques in a group of vermiculite workers in Marysville, Ohio. This RfC is based on the assumption that pleural plaques are associated with adverse lung function. In this study, we evaluated the association between pleural plaques and lung function in the Marysville worker cohort to determine whether they are associated with adverse effects or, rather, are more likely a biomarker of cumulative exposure to LAA.

Methods: We obtained the dataset on the Marysville worker cohort from University of Cincinnati, which included information on demographics, occupational exposures and results of chest high-resolution computed tomography (HRCT)/computed tomography (CT) scans and pulmonary function tests (PFTs). We used multivariate linear regression to estimate mean differences in several lung function parameters, and logistic regression to evaluate the odds of abnormal ventilatory patterns, among men with different pulmonary findings on HRCT/CT scans.

Results: No statistically significant differences in FEV1, FVC, FEV1/FVC, TLC, RV or DLCO were observed between workers with normal scans and those with pleural plaques but no other abnormalities. In contrast, workers with other abnormal findings had statistically significant lower FEV1, FVC, TLC and DLCO, compared with those with normal scans.

Conclusions: This study does not indicate that pleural plaques have a significant effect on lung function when past asbestos exposure is accounted for.

In plain English

This study re-analyzed existing data on workers at a Marysville, Ohio, plant that mainly processed Montana vermiculite ore. The aim was to see whether pleural plaques alone were linked to poorer lung function. The authors included 141 workers whose chest HRCT/CT scans and lung function tests were done within three years of each other. Of these, 57 had normal scans, 51 had pleural plaques only, and 33 had other lung abnormalities, with or without plaques. The analysis adjusted for smoking, body mass index and estimated past cumulative asbestos exposure. Compared with the normal group, the plaques-only group's adjusted percent predicted FEV1, FVC, TLC, RV and DLCO were lower by 2.55%, 3.79%, 3.32%, 1.80 and 4.53%. FEV1/FVC was slightly higher with plaques. None of these differences was statistically significant. Workers with other abnormalities had statistically significantly lower FEV1, FVC, TLC and DLCO, with differences of 10.0% to 16.0%. The authors concluded that pleural plaques did not adversely impact lung function in this cohort. They noted possible participation bias, likely substantial errors in exposure estimates, and that scans may miss early fibrosis.

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 re-analysis of an existing dataset on the Marysville worker cohort obtained from the University of Cincinnati
• Who was studied: 141 workers from the Marysville, Ohio, vermiculite worker cohort: 57 with normal HRCT/CT scans, 51 with pleural plaques only, and 33 with other lung abnormalities (with or without pleural plaques). The original cohort was 512 employees examined in the early 1980s. HRCT/CT scans came from a 2010 follow-up or from 2003 to 2009.
• Exposure: Occupational exposure to Libby amphibole asbestos (LAA) from Montana vermiculite ore. Past cumulative exposure to airborne asbestos fibers was estimated from job histories and an updated job exposure matrix. Mean exposures in fibers/cc-years were 1.47 (normal group), 7.64 (pleural plaques only) and 15.06 (other lung abnormalities). The groups differed significantly.
• Main results:
  • After adjustment for smoking, BMI and past cumulative asbestos exposure, there were no statistically significant differences in lung function between workers with pleural plaques only and workers with normal scans.
  • Compared with workers with normal scans, workers with pleural plaques only had adjusted mean percent predicted values that were lower by 2.55% (FEV1), 3.79% (FVC), 3.32% (TLC), 1.80 (RV) and 4.53% (DLCO). None of these differences was statistically significant; the table gives p values of 0.4, 0.2, 0.3, 0.73 and 0.08. The direction (lower with plaques) is shown by the article's contrast with FEV1/FVC and by the group means in Table 2. The minus signs themselves were lost in the text.
  • FEV1/FVC was slightly higher in the pleural-plaques-only group than in the normal group. The mean difference was 1.5% in the text and 1.45 in the table, with p 0.5.
  • All lung function parameters in the pleural-plaques-only comparison were within American Thoracic Society (2004) limits of normal lung function.
  • Workers with other lung abnormalities had statistically significantly lower FEV1, FVC, TLC and DLCO than workers with normal scans. Mean differences ranged from 10.0% to 16.0% (table: 12.21, 11.38, 10.05 and 15.97). Their differences in FEV1/FVC and RV were smaller and not statistically significant.
  • Pleural plaques only were not associated with increased odds of abnormal ventilatory patterns. The adjusted odds ratios were obstructive 0.71 (95% CI 0.05 to 10.1), restrictive 0.57 (0.17 to 1.89) and combined abnormal 0.56 (0.19 to 1.68).
  • For other lung abnormalities, the adjusted odds ratios were obstructive 2.91 (95% CI 0.41 to 20.4), restrictive 2.25 (0.61 to 8.35) and combined abnormal 2.48 (0.78 to 7.87). None was statistically significant.
• The authors' conclusion: The authors concluded that, because of the lack of statistical significance and uncertainty about the clinical relevance of the small decrements observed, pleural plaques do not adversely impact lung function in the Marysville worker cohort.
• Limitations the authors state:
  • Possible participation bias: of 512 workers in the original cohort, 431 were eligible and 141 provided HRCT/CT results and at least one lung function measurement. Workers with lung problems may have been more likely to take part.
  • Errors in estimating past cumulative fiber exposure were likely substantial, partly because no fiber measurements were available for 1957 to 1971.
  • HRCT/CT may miss some early subclinical fibrosis, which could misclassify workers between groups.

Topics

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

Medical terms in this study, explained in our Lexicon: Pleural Plaques, Libby amphiboles, vermiculite, Biomarker, Cumulative Exposure, Occupational Exposure, High-Resolution CT (HRCT), Pulmonary Function Test (PFT).

Related studies

• Comment on "pleural plaques and lung function in the Marysville worker cohort: a re-analysis" by Zu et al. (2016) — J.E. Lockey, K. Dunning, et al. (2017)
• Lung function, radiological changes and exposure: analysis of ATSDR data from Libby, MT, USA — D. Weill, G. Dhillon, et al. (2011)
• Systematic review of pleural plaques and lung function — L.E. Kerper, H.N. Lynch, et al. (2015)
• 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)
• Association between cumulative fiber exposure and respiratory outcomes among Libby vermiculite workers — T.C. Larson, V.C. Antao, et al. (2012)
• The natural course of lung function decline in asbestos exposed subjects with pleural plaques and asbestosis — M. Barnikel, P.M. Million, et al. (2019)

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