HRCT/CT and associated spirometric effects of low Libby amphibole asbestos exposure

Our plain-English summary of HRCT/CT and associated spirometric effects of low Libby amphibole asbestos exposure, by J.E. Lockey, K. Dunning, T.J. Hilbert, et al (Journal of Occupational and Environmental Medicine, 2015).

The study

• Authors: J.E. Lockey, K. Dunning, T.J. Hilbert, E. Borton, L. Levin, C.H. Rice, R.T. McKay, R. Shipley, C.A. Meyer, C. Perme, G.K. LeMasters
• Journal: Journal of Occupational and Environmental Medicine
• Published: 2015;57(1):6-13
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Objective: Evaluate the relationship between cumulative fiber exposure and high-resolution or conventional chest computed tomography (HRCT/CT) changes and spirometry of workers with Libby amphibole asbestos exposure.

Methods: Of the original 1980 cohort (n = 513), 431 were living and asked to participate. Images were evaluated for localized pleural thickening (LPT), diffuse pleural thickening (DPT), and parenchymal changes.

Results: A total of 306 participants provided either HRCT/CT scans (n = 191) or chest radiographs (n = 115). Of the 191 with HRCT/CT, 52.9% had pleural changes and 13.1% had parenchymal changes. Those with LPT only, LPT and/or DPT, or DPT and/or parenchymal changes had mean 6.1, 8.0, and 18.0 loss in percent predicted forced vital capacity, respectively.

Conclusions: Exposure to vermiculite containing amphibole fibers is associated with pleural and parenchymal HRCT/CT changes at low cumulative fiber exposure; these changes are associated with spirometric decrements.

In plain English

This study followed up workers first studied in 1980 at a plant in Marysville, Ohio, that expanded Libby vermiculite. The ore contains amphibole fibers, including richterite and tremolite, called Libby amphibole asbestos. Of 306 participants, 191 had chest CT scans; 101 of these (52.9%) had pleural changes and 25 (13.1%) parenchymal (lung tissue) changes. Exposure was estimated from job histories. Compared with workers with cumulative fiber exposure below 0.15 fiber-year/cm3, the four higher groups had significantly higher pleural-change risk: risk ratios 5.0 (95% CI 1.8 to 13.3), 6.8 (2.6 to 18.0), 10.4 (4.0 to 26.6) and 9.9 (3.8 to 25.4). Parenchymal-change risk ratios, adjusted for age and smoking pack-years, versus workers below 0.45 were 3.5 (1.0 to 11.6), 5.8 (2.0 to 17.3) and 4.0 (1.2 to 12.8) in the three higher groups, all significant. Versus normal scans, localized pleural thickening alone was linked to a 6.1 loss in percent predicted forced vital capacity; diffuse pleural thickening and/or parenchymal changes, to an 18.0 loss. The authors concluded that these changes occur at low cumulative exposure and are associated with reduced lung function.

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: Follow-up morbidity study of a worker cohort first examined in 1980, using chest CT or chest X-ray and spirometry
• Who was studied: Workers at a plant expanding Libby vermiculite in Marysville, Ohio, first studied in 1980 (513 in the original cohort, 431 living and eligible). Of these, 306 took part: 191 with HRCT/CT (175 HRCT, 16 conventional CT) and 115 with chest radiographs only, dating from 2003 to 2011.
• Exposure: Libby vermiculite ore containing amphibole fibers including winchite, richterite and tremolite (Libby amphibole asbestos). Exposure was expressed as cumulative fiber exposure (fiber-year/cm3), calculated by multiplying time in each job by job-exposure-matrix estimates and summing across jobs, mainly from 1957 to 1980.
• Main results:
  • 306 participants provided imaging: 191 with HRCT/CT and 115 with chest radiographs.
  • Among the 191 with HRCT/CT, 101 (52.9%) had pleural changes and 25 (13.1%) had parenchymal changes.
  • Among HRCT/CT participants, all cumulative fiber exposure categories of 0.15 fiber-year/cm3 or more had higher proportions with pleural changes than the reference group (below 0.15). Unadjusted risk ratios ranged from 5.0 to 10.4 and were significant.
  • Pleural changes, all 191 HRCT/CT participants, 0.15 to less than 0.45 fiber-year/cm3 versus below 0.15: unadjusted risk ratio 5.0 (95% CI 1.8 to 13.3).
  • Pleural changes, all 191 HRCT/CT participants, 0.45 to less than 1.35 fiber-year/cm3 versus below 0.15: unadjusted risk ratio 6.8 (95% CI 2.6 to 18.0).
  • Pleural changes, all 191 HRCT/CT participants, 1.35 to less than 10.00 fiber-year/cm3 versus below 0.15: unadjusted risk ratio 10.4 (95% CI 4.0 to 26.6).
  • Pleural changes, all 191 HRCT/CT participants, 10.00 fiber-year/cm3 or more versus below 0.15: unadjusted risk ratio 9.9 (95% CI 3.8 to 25.4).
  • In the lowest non-reference exposure category (0.15 to less than 0.45 fiber-year/cm3), 44% of HRCT/CT participants had pleural changes.
  • Among the 99 participants hired on or after 1972, exposure categories of 0.15 fiber-year/cm3 or more had significant risk ratios for pleural changes of 4.1 to 10.2.
  • Parenchymal changes on HRCT/CT were significantly associated with increasing cumulative fiber exposure and employment duration. Risk ratios were adjusted for age and pack years, and ranged from 3.5 to 5.8.
  • Parenchymal changes, all 191 HRCT/CT participants, 0.45 to less than 1.35 fiber-year/cm3 versus below 0.45: adjusted risk ratio 3.5 (95% CI 1.0 to 11.6).
  • Parenchymal changes, all 191 HRCT/CT participants, 1.35 to less than 10 fiber-year/cm3 versus below 0.45: adjusted risk ratio 5.8 (95% CI 2.0 to 17.3).
  • Parenchymal changes, all 191 HRCT/CT participants, 10 fiber-year/cm3 or more versus below 0.45: adjusted risk ratio 4.0 (95% CI 1.2 to 12.8).
  • In the 0.45 to less than 1.35 fiber-year/cm3 group, 15.8% (6/38) had parenchymal changes.
  • Compared with participants with normal HRCT/CT, localized pleural thickening alone was associated with a 6.1 loss in percent predicted FVC (P less than or equal to 0.05) and a 4.3 loss in percent predicted FEV1 (P = 0.14). Both estimates were adjusted for pack years and BMI.
  • Mean losses in percent predicted forced vital capacity were 6.1 for localized pleural thickening only, 8.0 for localized and/or diffuse pleural thickening, and 18.0 for diffuse pleural thickening and/or parenchymal changes.
  • The percent predicted FEV1/FVC ratio was not statistically significant in any spirometry model.
  • A sensitivity analysis added chest-radiograph participants and assumed the 125 living nonparticipants had normal imaging. It still showed significant risk ratios for pleural changes of 6.4 to 13.4 across exposure categories, compared with below 0.15 fiber-year/cm3.
• The authors' conclusion: The authors concluded that exposure to vermiculite containing amphibole fibers is associated with pleural and parenchymal HRCT/CT changes at low cumulative fiber exposure, and that these changes are associated with spirometric decrements.
• Limitations the authors state:
  • Possible participation bias: participants had higher mean cumulative fiber exposure and longer employment than living nonparticipants.
  • Possible exposure misclassification, especially for 1957 to 1971, when no fiber measurements were available.
  • HRCT slices were not contiguous, which may have slightly underestimated the prevalence of localized pleural thickening.
  • Using 16 conventional CT scans could slightly underestimate parenchymal changes compared with HRCT.
  • For 6.5% of participants, spirometry was done 6 to 7 years before the CT, which could underestimate the spirometric impact.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: High-Resolution CT (HRCT), Libby amphiboles, Asbestos Exposure, Spirometry, Pleural Thickening, Diffuse Pleural Thickening, CT Scan, Chest X-Ray.

Related studies

• Comment on "HRCT/CT and Associated Spirometric Effects of Low Libby Amphibole Asbestos Exposure" by Lockey et al (2015) — G. Tao, K. Zu, et al. (2015)
• Libby Amphibole Disease: Pulmonary Function and CT Abnormalities in Vermiculite Miners — A. Miller, J. Szeinuk, et al. (2018)
• Childhood exposure to Libby amphibole asbestos and respiratory health in young adults — P.H. Ryan, C.H. Rice, et al. (2017)
• Low levels of exposure to libby amphibole asbestos and localized pleural thickening — K.Y. Christensen, T.F. Bateson, et al. (2013)
• 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)
• Pulmonary inflammatory and fibrotic responses in Fischer 344 rats after intratracheal instillation exposure to Libby amphibole — D.J. Padilla-Carlin, M.C. Schladweiler, et al. (2011)

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