Causes of pulmonary impairment in asbestos-exposed individuals with diffuse pleural thickening

Our plain-English summary of Causes of pulmonary impairment in asbestos-exposed individuals with diffuse pleural thickening, by S.T. Kee, G. Gamsu, P. Blanc (American Journal of Respiratory and Critical Care Medicine, 1996).

The study

• Authors: S.T. Kee, G. Gamsu, P. Blanc
• Journal: American Journal of Respiratory and Critical Care Medicine
• Published: 1996;154(3 Pt 1):789-93
• Cited by: 38 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

To examine whether diffuse pleural thickening (DPT) causes impairment of pulmonary function independent of other manifestations of asbestos-related disease, we studied individuals selected from 1,150 men with occupational asbestos exposure who had undergone pulmonary function testing and computed tomographic (CT) scanning. The CT scans revealed 84 subjects with DPT as defined for CT. Of these 84 subjects, 53 eligible study cases were matched by age with a referent group without DPT from the same exposed group. No difference was demonstrated between cases and referents in smoking history, length of exposure, latency, or the proportion with either interstitial fibrosis or pleural plaques. Individuals with DPT demonstrated significantly reduced forced vital capacity (FVC) (p = 0.002) and diffusing capacity for carbon monoxide (DLCO) (p = 0.002) as compared with the referents. No difference was found in the two groups' FEV1 to FVC ratio (FEV1/FVC). Individuals with DPT and either interstitial fibrosis or pleural plaques showed a significantly lower FVC than did those with fibrosis or pleural plaques alone. Individuals with DPT and rounded atelectasis had similar pulmonary function to those with DPT and no rounded atelectasis. Subjects with DPT had a more frequent history of coronary bypass surgery than referents (19% versus 2%; p = 0.008). We conclude that subjects with DPT have restrictive pulmonary function and reduced diffusing capacity independent of other manifestations of asbestos-related disease.

In plain English

This study asked whether diffuse pleural thickening (DPT), a widespread sheet of scarring along the lung lining, reduces lung function on its own in asbestos-exposed people. The authors reviewed the records of 1,150 men referred between 1985 and 1993 for medicolegal evaluation of occupational asbestos exposure in shipyards or construction. CT scans showed DPT in 84 of them. Of these, 53 with complete records were compared with 53 age-matched exposed referents without DPT. The two groups had similar smoking history, exposure length, latency, and proportions with pleural plaques and interstitial fibrosis. The DPT cases had lower forced vital capacity (mean 67.8 versus 76.9 percent predicted) and lower diffusing capacity (71.7 versus 84.6 percent predicted) than referents. No significant difference was found between groups in airflow obstruction (FEV1/FVC ratio). People with DPT plus fibrosis, or DPT plus plaques, had lower FVC than those with fibrosis or plaques alone. Among DPT cases, lung function did not differ significantly with or without rounded atelectasis. More DPT cases than referents had had coronary bypass surgery (19% versus 2%). The authors concluded that subjects with DPT have restrictive lung function and reduced diffusing capacity independent of other asbestos-related disease.

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: Case-referent comparison using existing records: people with DPT on CT were compared with age-matched asbestos-exposed referents without DPT
• Who was studied: Records of 1,150 people referred between 1985 and 1993 for radiologic assessment as part of a medicolegal evaluation of occupational asbestos exposure. The abstract describes them as men. 84 had DPT on CT, a prevalence of 7.3%. The study compared 53 DPT cases with complete records against 53 referents. The referents were drawn from 110 otherwise matched candidates after 57 were excluded for missing data.
• Exposure: Occupational asbestos exposure in shipyards or construction, mainly between 1940 and 1970. Mean length of exposure was 24.5 years in DPT cases and 26.5 years in referents. Fiber types were not specified.
• Main results:
  • DPT cases and referents did not differ significantly in smoking history, length of exposure or latency. They also did not differ significantly in the proportions with pleural plaques (48 of 53 cases vs 44 of 53 referents) or interstitial fibrosis (39 vs 31).
  • Forced vital capacity was significantly lower in DPT cases than in referents: mean 67.8 percent predicted (SD 14.7) vs 76.9 (SD 14.8), p = 0.002.
  • Diffusing capacity for carbon monoxide (not corrected for lung volume) was significantly lower in DPT cases than in referents: mean 71.7 percent predicted (SD 19.7) vs 84.6 (SD 21.5), p = 0.002.
  • There was no significant difference between DPT cases and referents in the FEV1/FVC ratio, a measure of airflow obstruction: mean 73.7 vs 74.9.
  • Subjects with both DPT and interstitial fibrosis (n = 39) had a significantly lower FVC than subjects with fibrosis alone (n = 31): 66 vs 79 percent predicted, p less than 0.05. DLCO was also significantly lower than in the fibrosis-alone group (88). This held both for DPT alone (n = 14; 67) and for DPT with fibrosis (74).
  • Subjects with both DPT and pleural plaques (n = 48) had significantly lower FVC (69 vs 78 percent predicted) and DLCO (72 vs 88) than subjects with plaques alone (n = 44), p less than 0.05.
  • Rounded atelectasis was found in 27 of 53 DPT cases and in no referents. Pulmonary function did not differ significantly between DPT cases with and without rounded atelectasis.
  • More DPT cases (10; 19%) than referents (1; 2%) had had coronary bypass surgery, p = 0.008. DPT came before the surgery in six of these cases and after it in four. DPT cases with surgery had significantly lower DLCO than DPT cases without surgery (57 vs 75 percent predicted).
  • The authors repeated the analysis excluding the 11 pairs in which the case or the referent had had coronary surgery. FVC remained lower in DPT cases (68%, SD 15) than in referents (75%, SD 15; p = 0.02). DLCO also remained lower (75%, SD 20, vs 86%, SD 22; p = 0.01).
• The authors' conclusion: The authors concluded that subjects with DPT have restrictive pulmonary function and reduced diffusing capacity independent of other manifestations of asbestos-related disease. They also stated that DPT should be considered an independent cause of restriction and reduced DLCO in asbestos-exposed individuals.
• Limitations the authors state:
  • Only 5 DPT subjects did not have pleural plaques, which limited analysis of that group.
  • A lower proportion of eligible referents (48%) than DPT cases (63%) had complete records and could be studied. The authors described this difference as of borderline statistical significance.
  • The authors noted that HRCT detects only about 65% of asbestos-related lung fibrosis. They argued that undetected fibrosis was unlikely to explain the impairment seen in DPT cases.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Diffuse Pleural Thickening, Asbestos Exposure, CT Scan, Latency, Interstitial Fibrosis, Pleural Plaques, Diffusing Capacity (DLCO), FEV1.

Related studies

• Do asbestos-related pleural plaques on HRCT scans cause restrictive impairment in the absence of pulmonary fibrosis? — B. Clin, C. Paris, et al. (2011)
• Pleural abnormality as a cause of impairment and disability — P. Ernst, J. Bourbeau, et al. (1991)
• Asbestos-related diffuse pleural thickening — N. Fujimoto, K. Kato, et al. (2014)
• Diffuse pleural thickening following heart failure-related pleural effusions in an asbestos exposed patient — M. Evison, P. Barber (2015)
• Marked ventilation impairment due to progression of diffuse pleural thickening after cardiac surgery — T. Touma, R. Taira, et al. (2022)
• Diffuse thickening superimposed on circumscribed pleural thickening related to asbestos exposure — A. Miller, J.A. Miller (1993)

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