Pleural abnormalities in the Framingham Heart Study: prevalence and CT image features

Our plain-English summary of Pleural abnormalities in the Framingham Heart Study: prevalence and CT image features, by T. Araki, M. Yanagawa, F.J. Sun, et al (Occupational and Environmental Medicine, 2017).

The study

• Authors: T. Araki, M. Yanagawa, F.J. Sun, J. Dupuis, M. Nishino, Y. Yamada, G.R. Washko, D.C. Christiani, N. Tomiyama, G.T. O'Connor, G.M. Hunninghake, H. Hatabu
• Journal: Occupational and Environmental Medicine
• Published: 2017;74(10):756-761
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Background: The prevalence of pleural abnormalities in the general population is an epidemiologically important index of asbestos exposure, which has not been investigated since a radiography-based study in 1980.

Methods: We examined 2633 chest CT scans (mean 59.2 years, 50% female) from the Framingham Heart Study (FHS) for the presence and image characteristics of pleural plaques and diffuse pleural thickening. Demographics and pulmonary function were stratified by the presence of pleural abnormalities in association with interstitial lung abnormalities.

Results: Pleural abnormalities were present in 1.5% (95% CI 1.1% to 2.1%). Pleural lesions were most commonly bilateral (90.0%), multiple (77.5%), calcified (97.5%) and commonly involved posterior (lower: 92.5%, middle: 87.5%), anterior (upper: 77.5%, middle: 77.5%) and diaphragmatic areas (72.5%). Participants with pleural abnormalities were significantly older (75.7 years, p <0.0001), male (92.5%, p <0.0001), former or current smokers (80.0%, p <0.001) with higher pack-years (33.3, p <0.0001). No significant reduction was noted in pulmonary function measures (p=0.07-0.94) when adjusted for the associated covariates, likely due to small number of cases with pleural abnormalities. Information about prior history of asbestos exposure and occupation was not available.

Conclusions: Pleural plaques and diffuse pleural thickening are present on CT in 1.5% of the FHS cohort. The current prevalence of the pleural abnormalities is smaller than that reported in the previous population-based study using chest radiography, likely representing lower asbestos exposure in recent decades. The posterior portion of the pleura is most frequently involved but the anterior portion is also commonly involved.

© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2017. All rights reserved. No commercial use is permitted unless otherwise expressly granted.

In plain English

The authors examined chest CT scans taken from 2009 to 2011 of 2633 participants in the Framingham Heart Study in Massachusetts. Radiologists looked for pleural plaques and diffuse pleural thickening. Information on participants' past asbestos exposure and jobs was not available, and their clinical histories were not fully collected. These pleural abnormalities were found in 40 of 2633 people (1.5%, 95% CI 1.1% to 2.1%). Among those 40, most had lesions on both sides (90.0%) and calcification (97.5%). The lower back part of the pleura was most often involved (92.5%), but the upper and middle front parts were also common (77.5% each). People with the abnormalities were older, more often male and more often current or former smokers. After adjusting for age, sex, smoking and interstitial lung abnormalities, their lung function was not significantly lower. The authors noted the small number of cases, and that causes other than asbestos could not be ruled out. They concluded the prevalence was lower than the 3.9% reported in a 1976–1980 chest X-ray survey, likely reflecting lower asbestos exposure in recent decades.

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: Retrospective analysis of chest CT scans from a population-based cohort, with prevalence and image features of pleural abnormalities compared across groups
• Who was studied: 2633 participants (mean age 59.2 years, about half male) from the Offspring and Third Generation cohorts of the Framingham Heart Study, Framingham, Massachusetts, USA. They had non-contrast chest CT from 2009 to 2011.
• Exposure: Asbestos exposure was not measured. Information about prior asbestos exposure and occupation was not available, and clinical and occupational histories were not sufficiently obtained. The study assessed CT findings of pleural plaques and diffuse pleural thickening.
• Main results:
  • Pleural plaques and/or diffuse pleural thickening were found in 1.5% (95% CI 1.1% to 2.1%), 40 of 2633 participants.
  • Of the 40 cases, 13 had pleural plaques only (32.5%), 22 had a mix of plaques and diffuse pleural thickening (55%), and 5 had diffuse pleural thickening alone (12.5%).
  • Among the 40 cases, lesions were most commonly bilateral (90.0%), multiple (five or more, 77.5%), of moderate severity (50.0%) and calcified (97.5%).
  • Among the 40 cases, the most commonly involved locations were lower posterior (92.5%), middle posterior (87.5%), upper anterior (77.5%), middle anterior (77.5%) and diaphragmatic areas (72.5%).
  • Compared with participants with no pleural abnormality, those with pleural abnormalities were older (75.7 vs 58.6 years), more often male (92.5% vs 48.6%), more often former or current smokers (80.0% vs 50.5%) and had more pack-years (33.3 vs 8.9).
  • Interstitial lung abnormalities were more frequent in those with pleural abnormalities (17.5%) than without (6.1%). After adjustment for age, sex, smoking status and pack-years, this association was not significant (p=0.11).
  • Participants with pleural abnormalities showed slight reductions in FEV1 and DLCO in unadjusted analyses (p=0.04 and 0.02). After adjustment for age, sex, smoking status, pack-years and ILA status, there was no significant reduction in any lung function measure (p=0.42 and 0.07).
  • Participants with minor pleural changes (n=173) showed a slight but statistically significant decrease in DLCO in both unadjusted and adjusted models (adjusted -3%, 95% CI -5.6 to -0.4, p=0.02).
  • No participants younger than 50 years appeared to have pleural abnormalities.
• The authors' conclusion: The authors concluded that pleural plaques and diffuse pleural thickening were present on CT in 1.5% of the cohort. This was less than half the 3.9% reported from NHANES II (1976–1980) using chest radiography, likely representing lower asbestos exposure in recent decades. They also concluded that older age, male sex and cigarette smoking were associated with the abnormalities.
• Limitations the authors state:
  • The study was retrospective and occupational histories were not sufficiently obtained, so the pleural abnormalities were not necessarily due to asbestos. Other possible causes included pneumonia, empyema and thoracic surgeries.
  • Only a small number of participants had pleural abnormalities, which limited assessment of effects on lung function.
  • Because participants were not selected for particular diseases, statistical power could be diluted compared with an occupational cohort.
  • The cohort is mostly middle class and white, which may confound the results.
  • Results relied mostly on visual CT evaluation without pathological confirmation. Other structures could mimic minor pleural changes or diffuse pleural thickening.
  • Telling pleural plaques apart from diffuse pleural thickening was often ambiguous.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, CT Scan, Pleural Plaques, Diffuse Pleural Thickening, Interstitial, Bilateral, Pleura.

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