Low dose CT detected interstitial lung abnormalities in a population with low asbestos exposure

Our plain-English summary of Low dose CT detected interstitial lung abnormalities in a population with low asbestos exposure, by E.J.A. Harris, K.P. Lim, Y. Moodley, et al (American Journal of Industrial Medicine, 2021).

The study

• Authors: E.J.A. Harris, K.P. Lim, Y. Moodley, B. Adler, N. Sodhi-Berry, A. Reid, C.P. Murray, P.J. Franklin, A.B. Musk, N.H. de Klerk, F.J.H. Brims
• Journal: American Journal of Industrial Medicine
• Published: 2021;64(7):567-575
• Cited by: 9 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: The use of low dose CT (LDCT) chest is becoming more widespread in occupationally exposed populations. There is a knowledge gap as to heterogeneity in severity and the natural course of asbestosis after low levels of exposure. This study reports the characteristics of LDCT-detected interstitial lung abnormalities (ILA).

Methods: The Asbestos Review Program offers annual LDCT, health assessments, and pulmonary function tests to an asbestos-exposed cohort. Asbestosis was defined using the Helsinki Consensus statement and the presence of ILA defined using a protocol for occupational CT reports. At least two of three pulmonary function tests: forced expiratory volume in 1 s (FEV1 );​ forced vital capacity (FVC); and diffusion capacity for carbon monoxide (DLco) were required for analysis of physiological decline.

Results: From 1513 cases, radiological ILA was present in 485 (32%). The cohort was 83.5% male with a median age of 68.3 years and a median (IQR) asbestos exposure of 0.7 (0.09-2.32) fiber/ml-year. A mixed occupation, mixed asbestos fiber cohort comprised the majority of the cohort (65.8%). Of those with ILA, 40 (8.2%) had an FVC decline of ≥10% and 30 (6.2%) had a DLco decline of ≥15% per year. Time since first exposure, increasing tobacco exposure and reported dyspnea were independently associated with the presence of ILA.

Conclusions: In this population with relatively low asbestos exposure, LDCT-detected ILA that fits criteria for asbestosis is common, but physiological decline is not. This mild chronic stable phenotype of asbestos-associated ILA contrasts with the traditionally accepted views that asbestosis requires high exposures.

© 2021 Wiley Periodicals LLC.

In plain English

This study followed members of the Western Australia Asbestos Review Program, which offers yearly low dose CT chest scans, health checks and breathing tests to asbestos-exposed people. It included 1513 participants with at least one scan between August 2012 and July 2018 and at least two breathing tests a year or more apart. They were crocidolite workers from Wittenoom Gorge, former Wittenoom township residents, and a mixed-fiber, mixed-occupation group that made up 65.8%. Estimated median cumulative exposures were 1.19, 0.47 and 0.74 fiber/ml-years respectively. Interstitial lung abnormalities (ILA) meeting the Helsinki CT criteria for asbestosis were found in 485 (32%). Among them, 40 (8.2%) had an FVC decline of 10% or more per year and 30 (6.2%) a DLco decline of 15% or more per year. Longer time since first exposure, more pack-years of smoking and reported breathlessness were associated with ILA. Cumulative asbestos exposure did not differ between those with and without ILA. The authors concluded that such ILA was common in this relatively low-exposure population but lung function decline was not. They noted that participants were a surviving group and that no one had a biopsy.

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: Longitudinal cohort study of participants in an asbestos health surveillance program, using yearly low dose CT scans and lung function tests
• Who was studied: 1513 participants of the Western Australia Asbestos Review Program who had at least one low dose CT scan between August 23, 2012 and July 2, 2018 and at least two sets of pulmonary function tests. 83.5% were male, and the median age at first low dose CT was 68.3 years.
• Exposure: Three groups: crocidolite workers from Wittenoom Gorge, Wittenoom township residents, and a mixed-fiber, mixed-occupation group mostly from manufacturing industries. Estimated median cumulative exposures were 1.19 (IQR 0.21–4.37) fiber/ml-years for workers, 0.47 (0.025–1.76) for ex-residents and 0.74 (0.094–2.94) for the mixed exposure group.
• Main results:
  • ILA on low dose CT was present in 485 of 1513 participants (32%). Among those with ILA, linear opacities were seen in 93.6% and honeycombing in 10.5%.
  • There was little evidence that ILA progressed on CT: 2.7% of the cohort had an increase in linear opacity score of 2 or more.
  • Among the 485 with ILA, yearly lung function declines were: FVC decline of 5% or more in 71 (14.6%); FVC decline of 10% or more in 40 (8.2%); DLco decline of 15% or more in 30 (6.2%). Nine (1.8%) had both an FVC decline of 10% or more and a DLco decline of 15% or more.
  • Cumulative asbestos exposure did not differ between the groups with and without ILA (p = .66). Mean percent predicted FEV1, FVC and DLco were all statistically significantly lower in the ILA group.
  • In multivariate analysis, three factors were significantly associated with ILA: tobacco exposure (OR 1.007, 95% CI 1.001–1.01, per pack-year), time since first asbestos exposure (OR 1.06, 95% CI 1.04–1.07, per year), and MRC grade II dyspnea or above (OR 1.76, 95% CI 1.36–2.3).
  • Participants with ILA were more likely to self-report cough, wheeze and dyspnea. The proportion of ever-smokers and median tobacco smoke exposure did not differ between those with and without ILA.
  • Median cumulative exposure was 3.5 (IQR 0.6–12.6) fiber/ml-years in the nine participants with both FVC and DLco decline, versus 0.72 (0.1–3.2) in those without such decline. This difference did not reach statistical significance (p = .07).
• The authors' conclusion: The authors concluded that in this cohort with relatively low asbestos exposure, ILA fitting diagnostic criteria for asbestosis was common but physiological decline was not. They stated that this mild, chronic, stable form contrasts with the traditional view that asbestosis requires high exposure.
• Limitations the authors state:
  • Selection bias from survivorship and/or a healthy participant effect: people with more progressive disease and thoracic cancer had dropped out before the study.
  • Ultra-low dose CT may have under-recognized reticular changes, so true ILA cases may be slightly under-represented.
  • Because the program was a clinical service, gold-standard methods such as two readers and formal consensus were not used.
  • For participants with only two lung function measurements, the estimate of decline may be less accurate.
  • No participant had a biopsy, so some of the ILA may not be true asbestosis.
  • Comparisons with other cohorts need care because standard methods or criteria for describing ILA on CT have not been defined, and the study was designed before more recent descriptions of ILA.

Topics

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

Medical terms in this study, explained in our Lexicon: Interstitial, Asbestos Exposure, Pulmonary Function Test (PFT), FEV1, Diffusing Capacity (DLCO), Dyspnea.

Related studies

• Correlation of lung function with ultra-low-dose CT-detected lung parenchymal abnormalities: a cohort study of 1344 asbestos exposed individuals — F. Brims, E.J. Harris, et al. (2022)
• Interstitial Lung Abnormalities Detected by CT in Asbestos-Exposed Subjects Are More Likely Associated to Age — F. Laurent, I. Benlala, et al. (2021)
• Ultra low dose CT screen-detected non-malignant incidental findings in the Western Australian Asbestos Review Programme — C.P. Murray, P.M. Wong, et al. (2016)
• Ultra-low-dose chest computer tomography screening of an asbestos-exposed population in Western Australia — F.J. Brims, C.P. Murray, et al. (2015)
• Computed tomography-guided interstitial high-dose-rate brachytherapy in the local treatment of primary and secondary intrathoracic malignancies — N. Tselis, K. Ferentinos, et al. (2011)
• Low dose cabergoline induced interstitial pneumonitis — W. Frank, R. Moritz, et al. (1999)

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