Workers with Libby amphibole exposure: retrospective identification and progression of radiographic changes

Our plain-English summary of Workers with Libby amphibole exposure: retrospective identification and progression of radiographic changes, by T.C. Larson, C.A. Meyer, V. Kapil, et al (Radiology, 2010).

The study

• Authors: T.C. Larson, C.A. Meyer, V. Kapil, J.W. Gurney, R.D. Tarver, C.B. Black, J.E. Lockey
• Journal: Radiology
• Published: 2010;255(3):924-33
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Purpose: To assess how early pleural and/or parenchymal abnormalities consistent with asbestos exposure could be ascertained and to identify factors associated with progression.

Materials And Methods: Informed consent was obtained under an institutional review board-approved protocol. Multiple sequential chest radiographs obtained between 1955 and 2004 in 84 workers exposed to amphiboles associated with vermiculite in the town of Libby, Montana, were studied. A panel of three NIOSH B readers reviewed each worker's longitudinal chest radiograph series in reverse chronologic order and achieved a consensus reading for each radiograph. Measures of exposure were compared between workers with and those without progression of parenchymal and pleural abnormalities.

Results: Because of the way the study was designed, all subjects had pleural (n = 84) and/or parenchymal (n = 26) abnormalities on the most recent chest radiograph. Compared with other investigations that used different methods, this investigation revealed shorter latency periods (defined as the interval between date of hire and date of earliest radiographic detection) for circumscribed pleural plaque (median latency, 8.6 years) and pleural calcification (median latency, 17.5 years). Pleural abnormalities progressed in 64 workers, while parenchymal abnormalities progressed in 14. No significant differences were found with regard to measures of exposure between workers with and those without progression.

Conclusion: The latency period for the development of pleural plaques may be shorter than previously reported. Early plaques are subtle and may not be detectable except at retrospective review.

Copyright RSNA, 2010

In plain English

This retrospective study re-examined old chest X-ray series from 84 workers at the vermiculite mining and processing operation in Libby, Montana. The ore contained an asbestiform mineral the authors call Libby amphibole, mainly winchite, richterite and tremolite. The 1,272 X-rays dated from 1955 to 2004. Three NIOSH B readers reviewed each worker's series together, from newest to oldest, which let them trace abnormalities back to earlier films. Workers were included only if their latest X-ray already showed changes. Circumscribed pleural plaque was found in 83 workers and was first seen a median 8.6 years after hire. Pleural calcification was found in 37 (median 17.5 years), diffuse pleural thickening in 12 (median 27.0 years) and lung-tissue (parenchymal) changes in 26 (median 18.9 years). Pleural changes progressed in 64 workers and parenchymal changes in 14. Exposure measures did not differ significantly between workers with and without progression. The authors concluded that plaques may appear earlier than previously reported, but that early changes were subtle and often recognizable only in hindsight. The workers studied had higher exposures than the full worker group.

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: Retrospective review of serial chest radiographs. A consensus panel of three NIOSH B readers read each worker's radiograph series in reverse chronologic order, and exposure measures were compared between workers with and without progression.
• Who was studied: 84 former workers from the ATSDR-recreated Libby, Montana, vermiculite worker cohort (n = 1862). Of 184 workers with stored historical radiographs, 88 met the inclusion criteria (at least two posteroanterior radiographs spanning at least 4 years), and 84 were accepted after the first reading phase. Radiographs dated from 1955 to 2004, with 1272 radiographs reviewed in total. Compared with the whole cohort, eligible subjects worked longer, had greater cumulative fiber exposure and were older when hired.
• Exposure: Libby amphibole in vermiculite ore, described as winchite, richterite and tremolite in decreasing order of abundance. Exposure was estimated as lifetime cumulative fiber exposure (CFE) in fiber/mL-years from employment records and historical air sampling. Median CFE was 42.4 fiber/mL-years (25th–75th percentile 6.1–237.5) for the 88 available study subjects.
• Main results:
  • 83 of the 84 workers had circumscribed pleural plaque, with a median latency (time from hire to earliest detection) of 8.6 years.
  • Pleural calcification occurred in 37 workers (44%), with a median latency of 17.5 years. Diffuse pleural thickening occurred in 12 workers (14%), with a median latency of 27.0 years.
  • Parenchymal changes (small opacity profusion category 1/0 or greater) occurred in 26 workers (31%), with a median latency of 18.9 years. No parenchymal changes were detected on radiographs obtained within 10 years of hire.
  • Among workers with pleural (n = 84) or parenchymal (n = 26) changes, 64 (76%) and 14 (54%) respectively met the study's definition of progression.
  • Cumulative fiber exposure, hire year, years worked and age at hire were not significantly different between workers with and without progression. The multivariate logistic regression models did not yield significant results.
  • Controlling for age, the authors reported that increasing pleural calcification extent was associated with increased risk of pleural progression (odds ratio 2.1; 95% confidence interval 0.7, 6.5). Increasing circumscribed pleural plaque width was also associated with increased risk (odds ratio 3.5; 95% confidence interval 1.2, 10.2).
  • Eight workers already had circumscribed pleural plaque when hired, and two of these also had pleural calcification.
  • Among 38 workers whose plaque width increased from ILO category A to B, the median latency from hire was 17.6 years.
  • In one worker who had lived with a parent who was a vermiculite worker, the panel observed pleural plaque on a radiograph taken at age 9; the plaque progressed into adulthood.
  • Some workers had possible exposure outside the vermiculite operation (household contact, prior Libby residence or other asbestos-related jobs). Compared with other workers, they had shorter median latencies for circumscribed pleural plaque (5.1 vs 9.4 years, P = .5) and pleural calcification (11.3 vs 17.6 years, P = .76).
• The authors' conclusion: The authors concluded that circumscribed pleural plaque and calcification may become evident on chest radiographs earlier than previously reported. They also concluded that early plaques are subtle and may be detectable only at retrospective review. They suggested the earlier detection may reflect the retrospective method, community exposure before employment, and the unique composition of the Libby fibers.
• Limitations the authors state:
  • The workers with radiograph series were not representative of the entire worker cohort. They likely had greater cumulative exposure, which makes it less certain that the results apply to other workers.
  • The number of radiographs and the length of follow-up varied between workers, which may have hindered detection of progression.
  • The readers may have introduced a learning bias as they gained experience with the method.
  • The number of workers with parenchymal changes may have been too small to detect significant differences between exposure groups.
  • The retrospective method gave the readers a lower threshold for scoring subtle pleural changes. Such changes would be unlikely to be recognized when single radiographs are read prospectively.

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

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: Libby amphiboles, Asbestos Exposure, Informed Consent, Chest X-Ray, Amphibole Group, vermiculite, NIOSH, Latency.

Related studies

• Associations between radiographic findings and spirometry in a community exposed to Libby amphibole — T.C. Larson, M. Lewin, et al. (2012)
• 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)
• Low-level fiber-induced radiographic changes caused by Libby vermiculite: a 25-year follow-up study — A.M. Rohs, J.E. Lockey, et al. (2008)
• "Not your grandfather's pleural disease": rapid progression, ventilatory impairment, and chronic pleuritic pain from Libby vermiculite/amphibole — A. Miller (2014)
• Case-fatality study of workers and residents with radiographic asbestos disease in Libby, Montana — A. Miller, C.B. Black, et al. (2022)
• Vermiculite worker mortality: estimated effects of occupational exposure to Libby amphibole — T.C. Larson, V.C. Antao, et al. (2010)

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