Asbestosis

Overview
  • Asbestos refers to a family of related fibrous mineral silicates that are used in a large variety of manufacturing industries. Although usage of asbestos has declined in the US, asbestos is still commonly employed in developing countries. Asbestosis refers to a particular fibrosing respiratory pathology associated with inhalation of asbestos fibers. Although asbestosis is more common in those exposed to high levels in an occupational setting, asbestosis has been observed in those with more limited exposure.
Pathogenesis
  • The pathogenesis of asbestosis is similar to other Pneumoconioses (see page) and likely involves inflammatory activation of alveolar macrophages which phagocytose the asbestos fibers. Long-term inflammatory activation of these asbestos-laden macrophages results in chronic engagement of wound-healing process that ultimately leads to a diffuse interstitial pulmonary fibrosis. Beyond this fibrotic outcome, inhalation of asbestos fibers is also associated with certain cancers. Although asbestos fibers may not be potently carcinogenic themselves it is thought that they act as a nidus upon which other carcinogens can adsorb and thus reach high concentrations. This certainly appears to be the case with tobacco carcinogens and thus carcinogenic risk increases synergystically in individuals who have a history of asbestos exposure and are smokers.
Morphology
  • Asbestosis is characterized by a diffuse interstitial pulmonary fibrosis that can evolve with time into a picture of honeycomb lung. Alveolar macrophages may display "Asbestos Bodies", brown rod-like structures, representing internalized asbestos fibers covered in hemosiderin. Prior to overt fibrosis, patients may display fibrotic plaques on the parietal pleura that can be observed on chest radiography.
Clinical Consequences
  • Asbestosis is heralded by an insidious but progressive decline of respiratory function one to two decades after exposure. Additionally, the diffuse fibrosis of asbestosis often leads to a restrictive pattern of pulmonary function. Although the pleural plaques of asbestosis are typically asymptomatic, they can result in serous or bloody pleural effusions. As mentioned above, exposure to asbestos significantly increases the risk of several cancers. Malignant Mesotheliomas are virtually seen only in those with previous asbestos exposure, while the risk of bronchogenic carcinomas is increased, especially in those with a combined history of smoking and previous asbestos exposure.