Pleural Plaques and Their Effect on Lung Function: Libby Amphibole: Pleural Fibrosis and Its Consequences

Abstract

The recently published article in CHEST(September 2014) by Clark et al1Clark KA Flynn III, JJ Goodman JE Zu K Karmaus WJJ Mohr LC Pleural plaques and their effect on lung function in Libby vermiculite miners.Chest. 2014; 146: 786-794Abstract Full Text Full Text PDF PubMed Scopus (20) Google Scholar that reported no differences in pulmonary function in vermiculite miners in Libby, Montana, with pleural plaques only (PPO) raises many issues: Methodology: Miners with PPO on CT scan (n = 89) were compared with a small number (n = 16) said to show no pleural thickening (PT) and 35 showing primarily diffuse PT. A publication from the Center for Asbestos-Related Disease in Libby2Black B Szeinuk J Whitehouse AC et al.Rapid progression of pleural disease due to exposure to Libby amphibole: “Not your grandfather's asbestos related disease.”.Am J Ind Med. 2014; 57: 1197-1206Crossref PubMed Scopus (27) Google Scholar uses illustrative cases to demonstrate the atypical presentation of a great deal of PT resulting from asbestos exposure: thin lamellar thickening that is not recognized on radiographs or recognized in earlier stages on CT scan and that is more consistent with diffuse than with circumscribed PT. It is likely that the small no-PT comparison group included such patients, resulting in the failure to demonstrate a difference. The group with primarily diffuse PT showed values for FVC, FEV1, total lung capacity, and diffusing capacity that were statistically significantly lower than those of the small comparison group.Interpretation: The PPO group showed clearly decreased mean values for FVC (85.5% predicted), FEV1(83.7% predicted), and diffusing capacity of the lung for carbon monoxide (Dlco) (91.1% predicted) compared with the reference population from which the predicted values were calculated. It is erroneous to state that “all lung function parameters remained well within ATS/ERS [American Thoracic Society/European Respiratory Society] normal limits in the group” or that “group means were well within ATS/ERS limits of normal.”Background: The effects of asbestos-related PT on pulmonary function and clinical outcome have been demonstrated in large groups with traditional exposures and in those exposed to Libby amphibole. A study by Lilis et al3Lilis R Miller A Godbold J Chan E Selikoff IJ Pulmonary function and pleural fibrosis: quantitative relationships with an integrative index of pleural abnormalities.Am J Ind Med. 1991; 20: 145-161Crossref PubMed Scopus (56) Google Scholar of 1,185 insulators with PT showed a statistically significant effect of PPO on FVC, as well as a much larger effect from diffuse PT. A report by Miller et al4Miller A Warshaw R Nezamis J Diffusing capacity and forced vital capacity in 5,003 asbestos-exposed workers: relationships to interstitial fibrosis (ILO profusion score) and pleural thickening.Am J Ind Med. 2013; 56: 1383-1393Crossref PubMed Scopus (16) Google Scholar on 5,003 workers confirmed the effect of PPO on FVC and demonstrated a similar or greater effect on Dlco. Clark et al1Clark KA Flynn III, JJ Goodman JE Zu K Karmaus WJJ Mohr LC Pleural plaques and their effect on lung function in Libby vermiculite miners.Chest. 2014; 146: 786-794Abstract Full Text Full Text PDF PubMed Scopus (20) Google Scholar were not the first to report on diffusing capacity in asbestos-related PT. Larson et al5Larson TC Lewin M Gottschall EB Antao VC Kapil V Rose CS Associations between radiographic findings and spirometry in a community exposed to Libby amphibole.Occup Environ Med. 2012; 69: 361-366Crossref PubMed Scopus (33) Google Scholar reported on a large group exposed to Libby vermiculite and concluded that restrictive spirometry was associated with PPO and correlated with its severity: “Severe (PPO) may result in respiratory symptoms.” The effects of diffuse PT were greater. In 2004, Whitehouse6Whitehouse AC Asbestos-related pleural disease due to tremolite associated with progressive loss of lung function: serial observations in 123 miners, family members, and residents of Libby, Montana.Am J Ind Med. 2004; 46: 219-225Crossref PubMed Scopus (54) Google Scholar reported “accelerated” loss of lung function in 94 Libby patients with predominant PT: 3.2% predicted per year for vital capacity, 2.3 for total lung capacity, and 3.3 for Dlco. Black et al2Black B Szeinuk J Whitehouse AC et al.Rapid progression of pleural disease due to exposure to Libby amphibole: “Not your grandfather's asbestos related disease.”.Am J Ind Med. 2014; 57: 1197-1206Crossref PubMed Scopus (27) Google Scholar illustrate the rapid functional and clinical progression and prominence of chest pain in Libby patients. In conclusion, the article by Clark et al1Clark KA Flynn III, JJ Goodman JE Zu K Karmaus WJJ Mohr LC Pleural plaques and their effect on lung function in Libby vermiculite miners.Chest. 2014; 146: 786-794Abstract Full Text Full Text PDF PubMed Scopus (20) Google Scholar reporting on a small number of patients with PPO does not contravene the increasing recognition of Libby amphibole as a unique asbestos exposure that can result in progressive respiratory embarrassment from PT.