High resolution computed tomography and lung function in asbestos-exposed workers with normal chest radiographs

Our plain-English summary of High resolution computed tomography and lung function in asbestos-exposed workers with normal chest radiographs, by C.A. Staples, G. Gamsu, C.S. Ray, et al (The American Review of Respiratory Disease, 1989).

The study

• Authors: C.A. Staples, G. Gamsu, C.S. Ray, W.R. Webb
• Journal: The American Review of Respiratory Disease
• Published: 1989;139(6):1502-8
• Cited by: 122 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000167).

Abstract

Asbestos-exposed persons with normal chest radiographs can demonstrate parenchymal abnormalities on high resolution computed tomography (HRCT). We reviewed the HRCT, clinical presentation, and results of pulmonary function tests in 169 asbestos-exposed workers with normal chest radiographs (ILO less than 1/0). The HRCT was normal or near normal in 76 subjects (Group 1), abnormal but indeterminate for asbestosis in 36, and abnormal and suggestive of asbestosis in 57 (Group 2). The indeterminate subjects were excluded from further analysis. The subjects in Groups 1 and 2 were not significantly different in their duration of asbestos exposure, latency, smoking history, or in measurements of airflow obstruction (FEV1/FVC% and %FEV1). Both the vital capacity percent predicted and diffusing capacity percent predicted were significantly lower in the abnormal subjects (Group 2) than in the normal subjects (Group 1) (79.0 versus 86.2, p = 0.005; 78.2 versus 87.1, p = 0.024; independent t test). We conclude that in asbestos-exposed subjects with normal chest radiographs, HRCT can identify a group of subjects with significantly reduced lung function indicative of restrictive lung disease when compared with a group with normal or near-normal HRCT.

In plain English

This study reviewed high resolution CT (HRCT) scans, clinical findings and lung function tests in 169 workers with documented occupational asbestos exposure whose ordinary chest X-rays were read as normal (ILO profusion below 1/0). On HRCT, 76 workers had normal or near-normal lungs, 57 (34%) had abnormalities suggestive of asbestosis, and 36 had indeterminate findings and were left out of the comparison. The two compared groups did not differ significantly in years of exposure, time since first exposure, smoking, or airflow obstruction. The abnormal group had lower average vital capacity (79.0 versus 86.2 percent of predicted, p = 0.005) and diffusing capacity (78.2 versus 87.1 percent of predicted, p = 0.024), more breathlessness, and more extensive pleural plaques. Among the 76 workers whose HRCT was normal or near-normal, those with pleural plaques did not have significantly different lung function from those without. The authors concluded that HRCT can pick out a group of exposed workers with reduced lung function indicating restriction even when the chest X-ray is normal. Lung tissue was not examined to confirm asbestosis, and the group differences cannot be applied to individual patients.

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: Review and comparison of HRCT findings, clinical evaluation and pulmonary function tests in asbestos-exposed workers with normal chest radiographs, grouped by HRCT appearance
• Who was studied: The workers came from more than 400 asbestos-exposed workers being evaluated for asbestosis. Of 225 initially eligible workers with chest X-rays read as normal, 56 were excluded, leaving 169. Group 1 was 76 workers with normal or near-normal HRCT, which could include mild, focal abnormalities at no more than two levels. Group 2 was 57 workers with HRCT suggestive of asbestosis. Another 36 were indeterminate and excluded from analysis. The 133 analyzed workers had a mean age of 59 years (range 34 to 84), and 31 had never smoked. The article does not state where the workers came from or when the study took place; the authors were at the University of California Medical Center, San Francisco.
• Exposure: All workers had documented occupational asbestos exposure, with at least 10 years since first exposure. In the 133 analyzed workers, mean exposure duration was 20 years (range 2 to 52) and mean latency was 34 years (range 12 to 55). Fiber types and jobs are not reported.
• Main results:
  • 57 of the 169 workers with normal chest X-rays (34%) had HRCT features consistent with asbestosis.
  • Group 1 (normal or near-normal HRCT) and Group 2 (HRCT suggestive of asbestosis) did not differ significantly in exposure duration, latency, smoking history, or measures of airflow obstruction.
  • Vital capacity percent predicted was 86.2 in Group 1 versus 79.0 in Group 2 (p = 0.005). Diffusing capacity percent predicted was 87.1 versus 78.2 (p = 0.024). Both were significantly lower in Group 2.
  • Group 2 workers were older than Group 1 workers (62 versus 57 years; p = 0.028). The authors state that age did not explain the lung function difference because age-corrected values were used.
  • Group 2 reported greater dyspnea than Group 1 (2.22 versus 1.90; p = 0.02) and had more extensive pleural plaques (2.81 versus 2.43; p = 0.030).
  • Pleural plaques were present in 77% of Group 2 and 57% of Group 1.
  • Within Group 1 (the 76 workers with normal or near-normal HRCT), workers with and without pleural plaques did not differ significantly in airflow obstruction, lung restriction, or diffusing capacity. Those with plaques had longer exposure (20.8 versus 14.5 years; p less than 0.01).
  • The authors note that the lung function abnormalities in these workers would not have been severe enough to diagnose restrictive lung disease.
  • In a subset of 100 workers checked for emphysema on HRCT, 55 (55%) had it. Reduced FEV1/FVC% correlated with emphysema grade (r = 0.5; p = 0.001).
• The authors' conclusion: The authors concluded that HRCT is more sensitive than the ILO-classified chest X-ray for detecting lung abnormalities suggestive of asbestosis. They also concluded that HRCT can identify a functionally distinct subgroup of asbestos-exposed people with abnormalities indicating lung restriction. In their subjects, pleural plaques without lung fibrosis showed no restriction on standard tests, and obstructive lung function appeared mainly associated with emphysema.
• Limitations the authors state:
  • Asbestosis was not confirmed by examining lung tissue.
  • The group differences cannot be applied to the individual patient.
  • Lung function was not measured during exercise.
  • Workers with diffuse pleural thickening were excluded, and they may be a subset with pleural disease and impaired function.

Topics

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

Medical terms in this study, explained in our Lexicon: Chest X-Ray, High-Resolution CT (HRCT), Pulmonary Function Test (PFT), Asbestos Exposure, Latency, Obstructive Lung Disease, FEV1/FVC Ratio, FEV1.

Related studies

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• Pulmonary function, smoking habits, and high resolution computed tomography (HRCT) early abnormalities of lung and pleural fibrosis in shipyard workers exposed to asbestos — S. Neri, P. Boraschi, et al. (1996)
• Relationships (I) of International Classification of High-resolution Computed Tomography for Occupational and Environmental Respiratory Diseases with the ILO International Classification of Radiographs of Pneumoconioses for parenchymal abnormalities — T. Tamura, N. Suganuma, et al. (2015)
• Agreement between chest radiography and high-resolution computed tomography in diagnosing dust-related interstitial lung fibrosis — R.R. Tiwari (2015)
• Lung function not affected by asbestos exposure in workers with normal Computed Tomography scan — C. Schikowsky, M.K. Felten, et al. (2017)
• High-resolution computed tomography in cases with environmental exposure to asbestos in Turkey — F. Topçu, H. Bayram, et al. (2000)

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