Pulmonary abnormalities as a result of exposure to Libby amphibole during childhood and adolescence-The Pre-Adult Latency Study (PALS)

Our plain-English summary of Pulmonary abnormalities as a result of exposure to Libby amphibole during childhood and adolescence-The Pre-Adult Latency Study (PALS), by J. Szeinuk, C.W. Noonan, C.I. Henschke, et al (American Journal of Industrial Medicine, 2017).

The study

• Authors: J. Szeinuk, C.W. Noonan, C.I. Henschke, J. Pfau, B. Black, A. Miller, D.F. Yankelevitz, M. Liang, Y. Liu, R. Yip, L. Linker, T. McNew, R.M. Flores
• Journal: American Journal of Industrial Medicine
• Published: 2017;60(1):20-34
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: The purpose of Pre-Adult Latency Study was to evaluate lung findings among adults who had been environmentally exposed to Libby Amphibole only during childhood and adolescence.

Methods: Recruitment was restricted to volunteers who attended primary and/or secondary school, lived in Libby, MT, prior to age 23 years for males and 21 years for females and subsequently left the area. Subjects completed exposure and respiratory questionnaires, underwent pulmonary function tests (PFTs), and chest CT scans. A Pleural Score was calculated for degree and extent of pleural thickening. Logistic regression and multivariate linear regression were used.

Results: Of the 219 who met inclusion criteria, 198 participated. Pleural thickening was found in 96 (48%) of 198 participants. In almost half of these, it was of the lamellar type, not generally seen in exposure to other asbestos. Environmental Libby amphibole exposure was associated with pleural thickening, and the likelihood of pleural thickening increased with the number of years lived in the area. An inverse association between Pleural Score and PFT was found, which remained significant for FVC and DLco after additional sensitivity analyses.

Conclusions: Cumulative environmental exposure was associated with risk of pleural thickening. Among this cohort, quantitative measures of pleural thickening were associated with decreased PFT. Am. J. Ind. Med. 60:20-34, 2017. © 2016 Wiley Periodicals, Inc.

© 2016 Wiley Periodicals, Inc.

In plain English

This observational study looked at 198 adults who had lived in the Libby/Troy area of Montana as children or teenagers. They left before age 21 (women) or 23 (men) and never worked for the vermiculite mine. Of 750 volunteers, 219 met the criteria and 198 took part. Participants answered exposure questionnaires and had lung function tests and chest CT scans. Pleural thickening was found in 96 of 198 participants (48%). Of these, 49 had mainly the circumscribed type and 47 mainly the lamellar type. Compared with those who lived there less than 2 years before 1990, those who lived there 20 or more years had higher odds of pleural thickening (adjusted odds ratio 7.45, 95% CI 1.38–40.1). A combined environmental exposure score was also associated with it. Higher pleural scores were linked to lower lung function, and this stayed significant for forced vital capacity and diffusing capacity after sensitivity analyses. The authors concluded that cumulative environmental exposure was associated with pleural thickening. They noted there was no control group and that selection bias could not be ruled out.

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: Observational study of a volunteer cohort, each examined with questionnaires, pulmonary function tests and chest CT scans; no control group. Exposure was compared across levels within the cohort using logistic and linear regression.
• Who was studied: 198 adults who had lived in the Libby/Troy area of Montana for at least 6 months but left before age 21 (females) or 23 (males). All had at least 15 years between first potential exposure and the CT scan, and none had worked for or contracted with the Libby vermiculite mine. Of 750 volunteers, 219 met the inclusion criteria and 198 consented. 59.6% were female, and mean age at enrollment was 50.2 years (range 23 to 78).
• Exposure: Environmental exposure during childhood and adolescence to Libby amphibole, the asbestiform amphibole contaminating Libby vermiculite. It was measured by questionnaire as weighted years of contact with 11 environmental pathways (for example playing in vermiculite piles, the downtown ballfields, the school track, gardening with vermiculite, home insulation). It was also measured as household contact with a vermiculite mine worker, and the two were combined into a Total Environmental Score. Local non-mining jobs with possible vermiculite contact and jobs with commercial asbestos were recorded separately.
• Main results:
  • Pleural thickening was found on CT in 96 (48%) of the 198 participants; 25 of them had associated calcification.
  • Of the 96 with pleural thickening, 49 (51%) had only or predominantly circumscribed thickening and 47 (49%) only or predominantly lamellar thickening.
  • Compared with those who lived in the area less than 2 years before the mine closed in 1990, those with 20 or more years of residence had an odds ratio for pleural thickening of 7.45 (95% CI 1.38–40.1), adjusted for age, gender and BMI.
  • Per interquartile increase, adjusted odds ratios for pleural thickening were 1.33 (95% CI 1.02–1.73) for the environmental pathways score and 1.54 (0.97–2.45) for household contact with a vermiculite worker. The combined Total Environmental Score gave an odds ratio of 1.73 (1.14–2.64).
  • Local non-mining jobs with possible vermiculite contact were not associated with pleural thickening (adjusted OR 0.68, 95% CI 0.33–1.43). Jobs with commercial asbestos materials were also not associated with it (adjusted OR 0.85, 95% CI 0.34–2.13).
  • Men were more likely than women to have pleural thickening (described as three times more likely). Smoking was not associated with pleural thickening.
  • For the cohort as a whole, Libby amphibole exposure was not associated with pulmonary function test results.
  • A higher Pleural Score was associated with lower lung function. Slope estimates were larger for lamellar than for circumscribed thickening. After excluding six highly influential observations, the association remained significant for FVC and DLco.
  • 15 participants (8%) had CT findings suggestive of interstitial lung disease.
• The authors' conclusion: The authors concluded that cumulative environmental exposure was associated with risk of pleural thickening. In this cohort, quantitative measures of pleural thickening were associated with decreased pulmonary function. In the discussion they described this as a dose-response relationship.
• Limitations the authors state:
  • Participants had a high prevalence of overweight and obesity. This could reduce FVC and could lead to subpleural fat being misread as pleural thickening.
  • How well the sample represents the potential total population is difficult to determine. The authors cannot rule out selection bias, and symptoms may have motivated some people to participate.
  • There was no control population. The authors considered it unjustifiable to ask unexposed people to undergo CT radiation.

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, Latency, Pulmonary Function Test (PFT), CT Scan, Pleural Thickening, Diffusing Capacity (DLCO), Environmental Exposure.

Related studies

• 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)
• 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)
• Childhood exposure to Libby amphibole during outdoor activities — P.H. Ryan, G.K. LeMasters, et al. (2015)
• HRCT/CT and associated spirometric effects of low Libby amphibole asbestos exposure — J.E. Lockey, K. Dunning, et al. (2015)
• Case series: rheumatological manifestations attributed to exposure to Libby Asbestiform Amphiboles — R. Diegel, B. Black, et al. (2018)

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