Asbestos fibers and pleural plaques in a general autopsy population

Our plain-English summary of Asbestos fibers and pleural plaques in a general autopsy population, by A. Churg (The American Journal of Pathology, 1982).

The study

• Author: A. Churg
• Journal: The American Journal of Pathology
• Published: 1982;109(1):88-96
• Cited by: 55 articles, as counted by NIH iCite
• Read it: PubMed · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001753).

Abstract

It has been claimed that symmetric lower zone pleural or diaphargmatic plaques are markers of asbestos exposure both in asbestos workers and the general population. In this study, total pulmonary asbestos burden was analyzed for 29 patients selected because pleural plaques were found at autopsy, and the results were compared with values obtained for 25 patients who had no occupational asbestos exposure. The average number of asbestos bodies in the plaque groups was 1732/g wet lung, and in the control group, 42/g wet lung. Uncoated asbestos fibers were extracted from lung and counted, measured, and identified by morphologic examination, electron diffraction, and energy-dispersive x-ray spectroscopy. The total number of fibers/per gram wet lung in the plaque group (114 x 10(3)) was similar to that in the control group (99 x 10(3), as was the number of chrysotile fibers (51 x 10(3) versus 29 x 10(3)). However, the plaque patients had a marked increase in the number of the commercially used high aspect ratio amphiboles, amosite and crocidolite (50 x 10(3) versus 1 x 10(3). A retrospective history of fairly certain asbestos exposure was obtained for 16 of the plaque patients, and such a history correlated strongly with increased numbers of commercial amphiboles in lung. It is concluded that 1) in this general autopsy population, two subgroups of patients are present. About one half of the patients appear to have developed pleural plaques as a result of asbestos exposure, while the etiology of the plaques in the other half is unclear; 2) the presence of pleural plaques correlates with a modest (50-fold) increase in numbers of long high-aspect ratio commercial amphiboles in lung tissue but does not correlate with numbers of chrysotile fibers, noncommercial amphiboles, or the total number of asbestos fibers; 3) asbestos-induced lesions are related to a complex set of mineralogic parameters and not to mere numbers of fibers in lung.

In plain English

This autopsy study, by a single author, compared lung asbestos content in 29 general autopsy subjects chosen because they had pleural plaques with 25 control subjects without plaques. Plaque patients averaged 1732 asbestos bodies per gram of wet lung, compared with 42 in controls. Total uncoated fiber counts were similar (114 x 10^3 versus 99 x 10^3 fibers per gram of wet lung, where x 10^3 means thousands), as were chrysotile counts (51 x 10^3 versus 68 x 10^3). Plaque patients had far more of the commercial amphiboles amosite and crocidolite (50,000 versus 1,000 per gram). A history of fairly certain asbestos exposure was found for 16 plaque patients. Plaque patients with fewer than 100 bodies per gram had 6900 amosite and crocidolite fibers per gram, compared with 80,000 in those with more. Only chrysotile was found in the four plaques analyzed. The author concluded that about half the plaque patients appeared to have plaques from asbestos exposure and that the cause in the other half was unclear. The author cautioned that this does not mean chrysotile cannot cause plaques.

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: Autopsy case-control comparison of lung asbestos burden (asbestos bodies by light microscopy; uncoated fibers by electron microscopy, electron diffraction and energy-dispersive x-ray spectroscopy), with occupational histories obtained by interviewing relatives
• Who was studied: 29 general autopsy subjects with lower-zone parietal or diaphragmatic pleural plaques (28 men, 1 woman; mean age 65, range 47 to 82) and 25 control autopsy subjects without plaques (24 men, 1 woman; mean age 65, range 47 to 83). The article does not state where or when the autopsies were done.
• Exposure: Lung content of chrysotile, the commercial amphiboles amosite and crocidolite, and the noncommercial amphiboles tremolite, actinolite and anthophyllite. Among plaque patients, 11 had a history of shipyard work and 4 others had probable exposure as pipefitters, electricians, construction workers or insulators.
• Main results:
  • Mean asbestos body count was 1732 plus or minus 4149 bodies per gram of wet lung in the 29 plaque patients and 42 plus or minus 39 per gram in the controls.
  • Total uncoated asbestos fibers per gram of wet lung were similar: 114 x 10^3 in the plaque group and 99 x 10^3 in the control group.
  • Chrysotile fibers per gram of wet lung were 51 x 10^3 in the plaque group and 68 x 10^3 in the control group.
  • Amosite plus crocidolite fibers per gram of wet lung were 50 x 10^3 in the plaque group and 1 x 10^3 in the control group.
  • A history of fairly certain asbestos exposure was obtained for 16 of the plaque patients, and this history correlated strongly with higher numbers of commercial amphiboles in the lung.
  • Within the plaque group, patients with fewer than 100 asbestos bodies per gram had 6900 amosite and crocidolite fibers per gram of wet lung. Those with more than 100 bodies per gram had 80,000.
  • In the plaque group, asbestos body counts correlated with amosite fiber counts (Spearman 0.71, P less than 0.001) and with crocidolite fiber counts (0.49, P less than 0.006). They did not correlate with chrysotile or noncommercial amphiboles.
  • Only chrysotile fibers, and no amphiboles, were found in the four pleural plaques analyzed.
  • Diffuse interstitial fibrosis of the kind expected in asbestosis was found in only 1 plaque case, and whether that case counts as asbestosis was unclear.
• The authors' conclusion: The author concluded that this general autopsy population contained two subgroups. About half the plaque patients appeared to have developed plaques as a result of asbestos exposure, while the cause in the other half was unclear. Plaques correlated with increased long, high-aspect-ratio commercial amphiboles, not with chrysotile, noncommercial amphiboles or total fiber numbers.
• Limitations the authors state:
  • The control group could not be used to compare exposed persons with plaques against exposed persons without plaques, and the author stated the results should not be read that way.
  • The author cautioned against relying on occupational history to rule asbestos exposure in or out.
  • Replicate counts of the same sample differed by up to a factor of 2.
  • Classifying a glaucophane-like amphibole as crocidolite was, in the author's words, somewhat arbitrary.
  • The author stated the findings should not be taken to mean that chrysotile exposure does not produce pleural plaques.

Topics

Medical terms in this study, explained in our Lexicon: Pleural Plaques, Autopsy, Asbestos Exposure, Asbestos Bodies, Chrysotile, Aspect Ratio (Length-to-diameter ratio), Amphibole Group, Amosite.

Related studies

• Fiber size and number in workers exposed to processed chrysotile asbestos, chrysotile miners, and the general population — A. Churg, B. Wiggs (1986)
• Pleural plaques and exposure to mineral fibres in a male urban necropsy population — A. Karjalainen, P.J. Karhunen, et al. (1994)
• Asbestos Bodies Burden in the Autopsy Lung Tissue from General Thai Population — P. Incharoen, T. Hama, et al. (2019)
• Pleural plaques in the general population — G. Hillerdal (1991)
• Asbestos fibers in the general population — A. Churg, M.L. Warnock (1980)
• Nonasbestos pulmonary mineral fibers in the general population — A. Churg (1983)

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