Libby Amphibole Disease: Pulmonary Function and CT Abnormalities in Vermiculite Miners

Our plain-English summary of Libby Amphibole Disease: Pulmonary Function and CT Abnormalities in Vermiculite Miners, by A. Miller, J. Szeinuk, C.W. Noonan, et al (Journal of Occupational and Environmental Medicine, 2018).

The study

• Authors: A. Miller, J. Szeinuk, C.W. Noonan, C.I. Henschke, J. Pfau, B. Black, D.F. Yankelevitz, M. Liang, Y. Liu, R. Yip, T. McNew, L. Linker, R. Flores
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2018;60(2):167-173
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objective: This article describes radiologic and pulmonary function findings among miners exposed to Libby amphibole. Computed tomography (CT) permits the detection of the characteristic thin, lamellar pleural thickening (LPT).

Methods: Individuals who worked at the mine for a minimum of 6 months had chest CT and pulmonary function tests.

Results: Pleural thickening was noted in 223 (87%) of the 256 miners, parenchymal abnormalities in 49 (19%). LPT, found in 151 (68%), was associated with low values of forced vital capacity and diffusion capacity and significantly lower values in all pulmonary function tests when associated with parenchymal abnormalities.

Conclusion: Eighty-seven percent of miners exposed to Libby Amphibole had pleural abnormalities on CT. LPT alone, and more so with parenchymal abnormalities, resulted in decreased pulmonary function. The importance of this easily missed LPT is demonstrated by its high frequency and significant functional effects.

In plain English

This study looked at chest CT scans of 256 former workers at the Libby, Montana vermiculite mine, contaminated with amphibole asbestos the article calls Libby amphibole. All were patients of the Center for Asbestos Related Disease and had worked at least six months for the mine company, directly or as contractors. Breathing (pulmonary function) test data existed for 241; the analysis used tests done within a year of the CT, leaving 227, with fewer for some tests. Pleural thickening appeared in 223 miners (87.1%). Of these, 151 (67.7%) had only or mainly lamellar pleural thickening, a thin layer parallel to the ribs. The other 72 had only or mainly circumscribed pleural thickening. Lung-tissue (parenchymal) abnormalities like those of asbestosis appeared in 49 miners (19%). Miners with lamellar thickening plus lung-tissue abnormalities scored significantly lower on all breathing tests than those with normal scans. After accounting for other CT findings, lamellar thickening was linked to abnormal forced vital capacity compared with no pleural thickening (odds ratio 3.9, 95% CI 1.1 to 14). The authors concluded that lung function deficits were more often associated with lamellar than circumscribed thickening. They named sample selection as a possible limitation.

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 analysis of CT scans and pulmonary function tests in former mine workers who were patients of a clinic (CARD)
• Who was studied: 256 former workers (miners and contractors) of the Libby, Montana vermiculite mine who were patients at the Center for Asbestos Related Disease (CARD); 243 (95%) male. They were drawn from 477 CARD patients who identified themselves as miners. Pulmonary function data were available for 241, and 227 had FEV1 and FVC tests within one year of CT.
• Exposure: Occupational exposure to Libby amphibole asbestos that contaminated the vermiculite mine; a minimum of six months working directly or as a contractor for the mine company
• Main results:
  • Pulmonary function test data were available for 241 of the 256 miners (94%). Limiting to tests within one year of CT left 227 records with FEV1 and FVC data, with fewer for DLco (n=158) and lung volumes (n=135).
  • Among all 256 miners, 223 (87.1%) had pleural thickening on CT
  • Among the 223 miners with pleural thickening, 151 (67.7%) had only or predominantly lamellar pleural thickening (LPT); 72 (32.3%) had only or predominantly circumscribed pleural thickening (CPT)
  • 30 of the 256 miners (11.7%) had no CT abnormality
  • 49 miners (19%) had parenchymal abnormalities (irregular opacities, corresponding to those seen in asbestosis); 47 of them also had pleural thickening (37 LPT, 10 CPT)
  • 57 miners (22.3%) had emphysema without other parenchymal abnormalities; all but one of them (56 of 57) had pleural thickening
  • In the group with both LPT and parenchymal abnormalities, all pulmonary function tests were significantly lower than in the CT-negative group (p less than 0.05), adjusted for latency and smoking history
  • Diffusing capacity (DLco) was lowest in the group with LPT plus parenchymal abnormalities (p less than 0.002 compared with CT negative). It was also lower in miners with LPT than in those with CPT (p=0.016).
  • Adjusted only for latency and smoking history, miners with LPT had significantly elevated risk estimates for abnormal FEV1 and FVC compared with no pleural findings. Estimates for miners with CPT did not differ from those with no pleural thickening.
  • After further adjustment for other CT findings, the odds of abnormal FVC remained elevated among miners with LPT compared with no pleural thickening: OR 3.9 (95% CI 1.1 to 14)
  • Irregular opacities and emphysema were each consistently associated with abnormal pulmonary function tests
• The authors' conclusion: The authors concluded that occupational exposure to Libby amphibole leads to high frequencies of pleural thickening, mostly LPT. They also concluded that lung function deficits were more often associated with LPT than with CPT, particularly when parenchymal abnormalities were also present.
• Limitations the authors state:
  • Possible sample selection bias; the authors believe the sample is representative of the Libby amphibole mining population
  • Pack-years of smoking could not be calculated for a substantial portion of observations, so a categorical smoking variable was used in the main analysis

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: Libby amphiboles, vermiculite, Pleural Thickening, Pulmonary Function Test (PFT).

Related studies

• Pulmonary abnormalities as a result of exposure to Libby amphibole during childhood and adolescence-The Pre-Adult Latency Study (PALS) — J. Szeinuk, C.W. Noonan, et al. (2017)
• Rapid progression of pleural disease due to exposure to Libby amphibole: "Not your grandfather's asbestos related disease" — B. Black, J. Szeinuk, et al. (2014)
• Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in Libby, Montana — J.C. McDonald, J. Harris, et al. (2004)
• Asbestos-related pleural disease due to tremolite associated with progressive loss of lung function: serial observations in 123 miners, family members, and residents of Libby, Montana — A.C. Whitehouse (2004)
• The morbidity and mortality of vermiculite miners and millers exposed to tremolite-actinolite: Part III. Radiographic findings — H.E. Amandus, R. Althouse, et al. (1987)
• Radiographic abnormalities and exposure to asbestos-contaminated vermiculite in the community of Libby, Montana, USA — L.A. Peipins, M. Lewin, et al. (2003)

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