Progression of irregular opacities in asbestos miners

Our plain-English summary of Progression of irregular opacities in asbestos miners, by G.K. Sluis-Cremer, E. Hnizdo (British Journal of Industrial Medicine, 1989).

The study

• Authors: G.K. Sluis-Cremer, E. Hnizdo
• Journal: British Journal of Industrial Medicine
• Published: 1989;46(12):846-52
• Cited by: 25 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000159).

Abstract

All white and mixed race men who were employed in South African asbestos mines and mills between 30 November 1970 and 30 November 1975 were studied. The men who had two radiographs available, the first taken some time between the above two dates and the latest available radiograph which had to be at least two years after the first one numbered 1454: 793 continued exposure after the first radiograph and 661 did not. The films were read by a panel of three readers. Data available included age, years of exposure to asbestos and other mining, intensity of exposure to asbestos and other dust, and smoking habit. Progression was expressed as the difference between the average readings of radiograph 2--radiograph 1 in minor categories per year of irregular opacities. Changes in pleural abnormality were also measured. No differences of progression in the profusion or change in size of the irregular opacities were found between the two groups or in the number of zones affected. "New attacks" appeared equally frequently between the two groups. No difference in the change in extent of any type of pleural change was seen. It appears that once a dose of asbestos sufficient to initiate the disease has been retained it is inexorably progressive.

In plain English

This study followed South African asbestos miners and millers, mostly exposed to crocidolite and amosite (amphibole) asbestos, to see whether X-ray changes progressed after exposure stopped. Of 2185 white and mixed race men employed between 1970 and 1975, 1454 had a second X-ray at least two years later. Of these, 793 continued asbestos exposure after the first X-ray and 661 did not. Three readers compared each pair of films without knowing the time between them. Mean follow up was 8.0 and 8.7 years in the two groups. The authors found no differences between the groups in progression of irregular opacities or of pleural changes. New irregular opacities (from 0/0 to 1/0 or more) appeared in 80 of 648 men (12.3%) with continued exposure and 58 of 549 (10.6%) without, and the difference was not significant. In both groups, progression rate was predicted by age, initial profusion, smoking, and years of asbestos exposure before the first X-ray. The authors concluded that once enough asbestos to start the disease has been retained, the disease is inexorably progressive. They added that follow up may have been too short to show a benefit from stopping exposure.

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: Radiological follow-up (progression) study comparing chest X-rays taken at least two years apart, in men who did and did not continue asbestos exposure after the first X-ray
• Who was studied: 1454 white and mixed race men from South African asbestos mines and mills, drawn from 2185 men employed on 30 November 1970 or entering employment up to 30 November 1975. 793 had exposure after the first radiograph and 661 did not. Follow up ran to mid-1987, with a maximum of 16.5 years.
• Exposure: Predominantly South African amphibole asbestos (crocidolite and amosite); 85 men had chrysotile-only exposure. Exposure was measured in years and in fibre-years. Before the first X-ray, the group that continued exposure had a mean of 6.7 years and 38.4 fibre-years, against 4.2 years and 23.2 fibre-years for the group that stopped. After the first X-ray, the continuing group had a mean of 4.5 years and 6.2 fibre-years of further exposure.
• Main results:
  • No differences in the evolution of radiological change were found between men who continued exposure and men who did not.
  • Among men whose first X-ray read 0/0, new 'attacks' (1/0 or higher on the second X-ray) occurred in 80/648 (12.3%) of those with continued exposure and 58/549 (10.6%) of those without. The difference was not significant.
  • Among men first read 0/1, 53/88 (60%) in the exposed group and 46/69 (given as 66%, and as 67% in the Results section) in the unexposed group progressed to 1/0 or greater.
  • An increase in the size of irregular opacities was found by two out of three readers in 22.8% of the exposed group and 22.4% of the unexposed group.
  • The number of zones affected increased in 25.5% of the exposed group and 26.8% of the unexposed group.
  • The calculated area of pleural change progressed in 13.8% of the exposed group and 14.8% of the unexposed group. Costophrenic angle obliteration appeared in 3.9% and 4.4% respectively, and pleural calcification appeared or progressed in 2% of both groups.
  • In both groups, the significant predictors of progression rate were age at first radiograph, average profusion at first radiograph, smoking category, and years of asbestos exposure up to the first radiograph.
  • Among men who continued exposure, asbestos exposure after the first radiograph was a significant factor only when measured in fibre-years.
  • In the group not exposed after the first radiograph, average profusion on the first radiograph was the most important predictor of progression rate.
• The authors' conclusion: The authors concluded that once a dose of asbestos sufficient to initiate the disease has been retained in the lungs, the disease is inexorably progressive.
• Limitations the authors state:
  • Follow up was relatively short, so the time may have been too short, and the additional dose too low, for further exposure to have an effect.
  • With longer follow up, the men who ceased exposure might be shown to have benefited.
  • Fibre concentration estimates from earlier years may not have been accurate enough. The authors offered this as a possible reason why fibre-years was a weaker predictor than years of exposure.
  • Readers disagreed more often when one of them thought progression was present.

Topics

Medical terms in this study, explained in our Lexicon: Habit.

Related studies

• Factors influencing the reading of small irregular opacities in a radiological survey of asbestos miners in South Africa — G.K. Sluis-Cremer, P.A. Hessel, et al. (1989)
• Cigarette smoking and small irregular opacities — W. Weiss (1991)
• Irregular opacities in the lung, occupational asthma, and airways dysfunction in aluminum workers — K.H. Kilburn, R.H. Warshaw (1992)
• Effect of tobacco smoking on the presence of asbestosis at postmortem and on the reading of irregular opacities on roentgenograms in asbestos-exposed workers — E. Hnizdo, G.K. Sluis-Cremer (1988)
• Progression of small, irregular opacities in chest radiographs of former asbestos workers — B. Świątkowska, W. Sobala, et al. (2012)
• Thickening of pulmonary interlobar fissures: exposure-response relationship in crocidolite and amosite miners — A. Solomon, L.M. Irwig, et al. (1979)

Browse more research in British Journal of Industrial Medicine, or return to medical research.