Associations between radiographic findings and spirometry in a community exposed to Libby amphibole

Our plain-English summary of Associations between radiographic findings and spirometry in a community exposed to Libby amphibole, by T.C. Larson, M. Lewin, E.B. Gottschall, et al (Occupational and Environmental Medicine, 2012).

The study

• Authors: T.C. Larson, M. Lewin, E.B. Gottschall, V.C. Antao, V. Kapil, C.S. Rose
• Journal: Occupational and Environmental Medicine
• Published: 2012;69(5):361-6
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Among asbestos-exposed individuals, abnormal spirometry is usually associated with parenchymal abnormalities or diffuse pleural thickening. Localised pleural thickening (LPT), the most common abnormality associated with asbestos exposure, is typically thought to be a marker of exposure with little clinical consequence. Our objective was to determine if abnormal spirometry is associated with LPT independent of other abnormalities, using data from community-based screening conducted in Libby, Montana.

Methods: Subjects were a subset of screening participants comprising persons with interpretable spirometry and chest radiograph results (n=6475). Chest radiographs were independently evaluated by two or three B readers, and participants were classified by mutually exclusive categories of spirometry outcome: normal, restriction, obstruction or mixed defect.

Results: Restrictive spirometry was strongly associated with parenchymal abnormalities (OR 2.9; 95% CI 1.4 to 6.0) and diffuse pleural thickening (OR 4.1; 95% CI 2.1 to 7.8). Controlling for the presence of these abnormalities as well as age, smoking status and other covariates, restrictive spirometry was also associated with LPT (OR 1.4; 95% CI 1.1 to 1.8). The risk of restrictive spirometric findings correlated with the severity of LPT.

Conclusions: In this large community-based screening cohort, restrictive spirometry is significantly associated with LPT, indicating that this abnormality may result in lung function impairment. Physicians treating patients exposed to Libby amphibole should be aware that LPT may have functional consequences.

In plain English

This study analysed screening data from Libby, Montana, where vermiculite was mined and processed from 1925 to 1990. The vermiculite contained amphibole fibres: winchite, richterite, tremolite and actinolite. The Agency for Toxic Substances and Disease Registry began the screening in 2000. 6476 participants had usable breathing tests (spirometry) and chest radiographs, each read by two or three B readers. After adjusting for age, sex, smoking, body mass index, exposure group and other factors, a restrictive breathing pattern was associated with lung tissue (parenchymal) abnormalities (odds ratio 2.9; 95% CI 1.4 to 6.0) and with diffuse pleural thickening (4.1; 2.1 to 7.8). Its association with localised pleural thickening was weaker (1.4; 1.1 to 1.8). For localised thickening, odds of restriction were statistically significant only when a severity index combining its width and extent was above the median (1.9; 1.5 to 2.5). The authors concluded that localised pleural thickening may have functional consequences. They noted that most participants were overweight or obese and readers knew of the Libby exposures. They also noted that fibrosis invisible on radiographs might explain part of the association.

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: Analysis of community-based health screening data (questionnaire, spirometry and chest radiographs), using logistic regression; the authors call it a community-based screening cohort
• Who was studied: Participants in a community screening programme in Libby, Montana, USA, begun in 2000. 7307 people consented. 6476 had both interpretable spirometry and chest radiographs; 831 were excluded, 599 of them because they were minors and had no radiograph.
• Exposure: Amphibole fibres in Libby vermiculite (winchite, richterite, tremolite and actinolite). Participants were grouped as occupational (exposure to vermiculite or asbestos), household contacts of Libby vermiculite workers, or residents with neither, with length of residence and number of community exposure pathways also recorded.
• Main results:
  • Restrictive spirometry was associated with parenchymal abnormalities (OR 2.9; 95% CI 1.4 to 6.0; 50 participants with these abnormalities) and with diffuse pleural thickening (OR 4.1; 95% CI 2.1 to 7.8; 58 participants).
  • Controlling for parenchymal abnormalities, diffuse pleural thickening, age, smoking and other covariates, restrictive spirometry was associated with localised pleural thickening (OR 1.4; 95% CI 1.1 to 1.8; 708 participants with LPT). This was the weakest of the associations but statistically significant.
  • Pleural calcification (254 participants) was also associated with restrictive spirometry (OR 1.7; 95% CI 1.2 to 2.4).
  • Among the 708 participants with localised pleural thickening, 463 (65%) had normal spirometry. Restriction was the most common abnormality (146; 21%).
  • The odds of restriction rose with the degree of pleural thickening, measured by a severity index combining the width and extent of thickening. For localised thickening, the odds ratio was 1.3 (95% CI 1.0 to 1.7) at or below the median index of 2.5, and 1.9 (95% CI 1.5 to 2.5) above the median. It was statistically significant only above the median. For diffuse thickening above the median, the odds ratio was 5.6 (95% CI 2.7 to 11.6).
  • Among participants with restrictive spirometry, those with a high localised pleural thickening index were compared with those with an index of 0. Their odds of impairment were 1.7 (95% CI 1.3 to 2.5) for mild, 2.1 (95% CI 1.4 to 3.2) for moderate and 2.3 (95% CI 0.8 to 6.7) for severe impairment. Only the severe result was not statistically significant, which the authors attributed likely to small numbers (6 people).
  • Compared with national NHANES III data, adjusted for age, race, body mass index and smoking, all adult participants with spirometry had a rate ratio of 1.3 for restriction (observed 776, expected 587.9; 95% CI 1.2 to 1.4). The rate ratio for obstruction was 1.1 (observed 576, expected 527.9; 95% CI 1.0 to 1.2).
  • There were no strong trends between abnormal spirometry and the exposure measures: exposure category, length of residence in Libby and number of exposure pathways.
• The authors' conclusion: The authors concluded that, in this cohort of community screening participants, localised pleural thickening was statistically associated with restrictive spirometry, and that this association correlated with the extent of thickening. They concluded that physicians treating patients exposed to Libby amphibole should be aware that localised pleural thickening may have functional consequences.
• Limitations the authors state:
  • Most participants (4591, 71%) were overweight or obese. Obesity is associated with reduced FVC and restrictive changes, and with more apparent pleural thickening on radiographs. The authors controlled for body mass index in all models.
  • Only spirometry was available, not more detailed lung function tests, because the data came from screening not intended for research.
  • Possible reader bias: the readers knew about the exposures in Libby, and no negative radiographs were deliberately included as controls.
  • Radiographs have low sensitivity for pneumoconiosis. Some of the restriction attributed to localised pleural thickening may be due to lung fibrosis not visible on radiographs. In a separate subset of 353 participants who had HRCT, 12 (3%) without parenchymal abnormalities on radiograph had them on HRCT.

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: Asbestosis, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Spirometry, Libby amphiboles, Diffuse Pleural Thickening, Pleural Thickening, Asbestos Exposure, Chest X-Ray.

Related studies

• Workers with Libby amphibole exposure: retrospective identification and progression of radiographic changes — T.C. Larson, C.A. Meyer, et al. (2010)
• Radiographic abnormalities and exposure to asbestos-contaminated vermiculite in the community of Libby, Montana, USA — L.A. Peipins, M. Lewin, et al. (2003)
• 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)
• Association between cumulative fiber exposure and respiratory outcomes among Libby vermiculite workers — T.C. Larson, V.C. Antao, et al. (2012)
• Asbestos-related radiographic findings among household contacts of workers exposed to Libby vermiculite: impact of workers' personal hygiene practices — T.J. Hilbert, A. Franzblau, et al. (2013)
• "Not your grandfather's pleural disease": rapid progression, ventilatory impairment, and chronic pleuritic pain from Libby vermiculite/amphibole — A. Miller (2014)

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