From Mount Sinai School of Medicine; and Pulmonary Function Laboratory, Beth Israel Medical Center.
CORRESPONDENCE TO: Albert Miller, MD, FCCP, Pulmonary Division, Dazian 7, Beth Israel Medical Center, 1st Ave at 16th St, New York, NY 10003; e-mail: firstname.lastname@example.org
FINANCIAL/NONFINANCIAL DISCLOSURES: The author has reported to CHEST that subsequent to the submission of this article he was requested, and agreed, to serve as a limited consultant to the Center for Asbestos Related Disease in Libby, Montana.
Reproduction of this article is prohibited without written permission from the American College of Chest Physicians. See online for more details.
The recently published article in CHEST (September 2014) by Clark et al1 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 Libby2 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 al3 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 al4 on 5,003 workers confirmed the effect of PPO on FVC and demonstrated a similar or greater effect on Dlco. Clark et al1 were not the first to report on diffusing capacity in asbestos-related PT.
Larson et al5 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, Whitehouse6 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 al2 illustrate the rapid functional and clinical progression and prominence of chest pain in Libby patients.
In conclusion, the article by Clark et al1 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.
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