Chrysotile vs. Libby Amphibole
Important differences in physiological responses to fiber types are being observed. Because of their flexible morphology, Chrysotile fibers were the most commonly used commercial fiber type. Most of the medical science we have learned has been based on disease caused by Chrysotile fibers, not Amphibole. Unlike other ARD populations, diffuse highly inflamed pleuritis has an increased incidence in Libby Amphibole disease, causing intense chest pain, rare in Chrysotile disease.
Significant lung disease from Chrysotile typically presents after prolonged occupational exposure. Disease caused by Chrysotile typically manifests as pleural disease with primary progression being evident as increased interstitial fibrosis, with chest pain and rapid progression being rare. Chrysotile Fibers are less bio-persistent, having a shorter half life than amphiboles, disease latency is typically around 10 years from exposure.
Low-Dose Environmental Exposure Causes Disease
ATSDR and CDC studies show significant excess mortality from lung cancer, mesothelioma and Asbestos Related Disease (ARD) in the entire Libby community. The majority of individuals with disease did not directly work for the mine. Non-malignant EPA toxicity values have not yet been established for Libby Amphibole asbestos, but are expected to be much less than current permissible levels for all asbestos fiber types.
Predominance of Pleural Disease Progression
Pleural fibrosis is the most common presentation of all asbestos fiber types. Traditional medical knowledge of asbestos disease is based on understanding of the Chrysotile asbestos fiber disease, which primarily progresses to interstitial fibrosis or “Asbestosis.” In contrast, the unique chemical and structural make-up of Libby Amphibole asbestos results in unique disease manifestation, primarily causing thin lamellar progressive pleural based fibrosis, with limited to no evidence of interstitial fibrosis. (Peipins, 2003)
Many Cases Are Not Evident On CXR & Require HRCT For Identification
The most common radiographic finding is thin, < 5mm, lamellar, non-calcified pleural thickening that lines the posterior-lateral chest. Generally LA cases lack calcified circumscribed plaquing. In that absence, the thin lamellar thickening is frequently not reported. If recognized, pleural thickening is often misinterpreted as pleural based fat or muscle shadow. Lamellar non-calcified pleural thickening is a non-specific structural finding that must be clinically correlated within the context of adequate exposure history and latency. (Muravov, 2005; Larson, 2010; Larson, 2012)
Unique Clinical Presentation
Patients can present with restrictive, obstructive, or normal pulmonary function findings including maintaining a normal DLCO. A high percentage of individuals with pleural disease experience chest and thoracic pain of variable character, severity, and duration. Pleural fibrosis has been observed to follow rapid progression, including progression from normal lung functions to death within six years. (Wright, 2002)
Libby Amphibole Asbestos
Amphibole fibers have extended bio-persistence, LA diseases typically have a latency of 10-40 years. Vermiculite, a non-toxic fibrous mineral rock formation, was discovered in Lincoln County, Montana, in 1916 by E.N. Alley. Alley formed the Zonolite Company and began commercial production of vermiculate in 1921. Virtually all vermiculite mined from Zonolite Mountain was contaminated with one of the more toxic forms of asbestos called Libby Amphibole asbestos.