A plaque caused by asbestosis on the diaphragmatic pleura with a verrucous appearance.
|Classification and external resources|
Asbestosis is a chronic inflammatory and fibrotic medical condition affecting the parenchymal tissue of the lungs caused by the inhalation and retention of asbestos fibers. It usually occurs after high intensity and/or long-term exposure to asbestos (particularly in those individuals working on the production or end-use of products containing asbestos) and is therefore regarded as an occupational lung disease. People with extensive occupational exposure to the mining, manufacturing, handling, or removal of asbestos are at risk of developing asbestosis. Sufferers may experience severe dyspnea (shortness of breath) and are at an increased risk for certain malignancies, including lung cancer but especially mesothelioma. Asbestosis specifically refers to interstitial (parenchymal) fibrosis from asbestos, and not pleural fibrosis or plaquing.
Signs and symptoms
The signs and symptoms of asbestosis do not manifest until after an appreciable latency (time since first exposure), often several decades under current conditions in the US. The primary symptom of asbestosis is generally the slow onset of dyspnea, especially on exertion. Clinically advanced cases of asbestosis may lead to respiratory failure. On auscultation of the lungs, the physician may hear inspiratory rales.
The characteristic pulmonary function finding in asbestosis is a restrictive ventilatory defect. This manifests as a reduction in lung volumes, particularly the vital capacity (VC) and total lung capacity (TLC). The TLC may be reduced through alveolar wall thickening; however this is not always the case. Large airway function, as reflected by FEV1/FVC, is generally well preserved. In the more severe cases, the drastic reduction in lung function due to the stiffening of the lungs and reduced TLC may induce right-sided heart failure (cor pulmonale). In addition to a restrictive defect, asbestosis may produce reduction in diffusion capacity and arterial hypoxemia.
Asbestosis is the scarring of lung tissue (beginning around terminal bronchioles and alveolar ducts and extending into the alveolar walls) resulting from the inhalation of asbestos fibers. There are two types of fibers: amphibole (thin and straight) and serpentine (curved). All forms of asbestos fibers are responsible for human disease as they are able to penetrate deeply into the lungs. When such fibers reach the alveoli (air sacs) in the lung, where oxygen is transferred into the blood, the foreign bodies (asbestos fibers) cause the activation of the lungs local immune system and provoke an inflammatory reaction dominated by lung macrophages that respond to chemotactic factors activated by the fibers. This inflammatory reaction can be described as chronic rather than acute, with a slow ongoing progression of the immune system attempting to eliminate the foreign fibers. Macrophages phagocytose (ingest) the fibers and stimulate fibroblasts to deposit connective tissue. Due to the asbestos fibers natural resistance to digestion, some macrophages are killed and others release cytokines, attracting further lung macrophages and fibrolastic cells that synthesize fibrous scar tissue, which eventually becomes diffuse and can progress in heavily exposed individuals. This tissue can be seen microscopically soon after exposure in animal models. Some asbestos fibers become layered by an iron-containing proteinaceous material (ferruginous body) in cases of heavy exposure where about 10% of the fibers become coated. Most inhaled asbestos fibers remain uncoated. About 20% of the inhaled fibers are transported by cytoskeletal components of the alveolar epithelium to the interstitial compartment of the lung where they interact with macrophages and mesenchymal cells. The cytokines, transforming growth factor beta and tumor necrosis factor alpha, appear to play major roles in the development of scarring inasmuch as the process can be blocked in animal models by preventing the expression of the growth factors.The result is fibrosis in the interstitial space, thus asbestosis. This fibrotic scarring causes alveolar walls to thicken, which reduces elasticity and gas diffusion, reducing oxygen transfer to the blood as well as the removal of carbon dioxide. This can result in shortness of breath, a common symptom exhibited by individuals with asbestosis.
- Evidence of structural pathology consistent with asbestosis, as documented by imaging or histology
- Evidence of causation by asbestos as documented by the occupational and environmental history, markers of exposure (usually pleural plaques), recovery of asbestos bodies, or other means
- Exclusion of alternative plausible causes for the findings
The abnormal chest x-ray and its interpretation remain the most important factors in establishing the presence of pulmonary fibrosis. The findings usually appear as small, irregular parenchymal opacities, primarily in the lung bases. Using the ILO Classification system, "s", "t", and/or "u" opacities predominate. CT or high-resolution CT (HRCT) are more sensitive than plain radiography at detecting pulmonary fibrosis (as well as any underlying pleural changes). More than 50% of people affected with asbestosis develop plaques in the parietal pleura, the space between the chest wall and lungs. Once apparent, the radiographic findings in asbestosis may slowly progress or remain static, even in the absence of further asbestos exposure. Rapid progression suggests an alternative diagnosis.
Asbestosis resembles many other diffuse interstitial lung diseases, including other pneumoconiosis. The differential diagnosis includes idiopathic pulmonary fibrosis (IPF), hypersensitivity pneumonitis, sarcoidosis, and others. The presence of pleural plaquing may provide supportive evidence of causation by asbestos. Although lung biopsy is usually not necessary, the presence of asbestos bodies in association with pulmonary fibrosis establishes the diagnosis. Conversely, interstitial pulmonary fibrosis in the absence of asbestos bodies is most likely not asbestosis. Asbestos bodies in the absence of fibrosis indicate exposure, not disease.
There is no curative treatment for asbestosis. Oxygen therapy at home is often necessary to relieve the shortness of breath and correct underlying hypoxia. Supportive treatment of symptoms includes respiratory physiotherapy to remove secretions from the lungs by postural drainage, chest percussion, and vibration. Nebulized medications may be prescribed in order to loosen secretions or treat underlying Chronic Obstructive Pulmonary Disease. Immunization against pneumococcal pneumonia and annual influenza vaccination is administered due to increased sensitivity to the diseases. Patients are at increased risk for certain malignancies. If the patient smokes, cessation reduces further damage. Periodic PFTs, chest x-rays, and clinical evaluations, including cancer screening/evaluations, are given to detect additional hazards.
The death of English textile worker Nellie Kershaw in 1924 from pulmonary asbestosis was the first case to be described in medical literature, and the first published account of disease attributed to occupational asbestos exposure. However, her former employers (Turner Brothers Asbestos) denied that asbestosis even existed because the medical condition was not officially recognised at the time. As a result, they accepted no liability for her injuries and paid no compensation, either to Kershaw during her final illness or to her bereaved family after she had died. Even so, the findings of the inquest into her death were highly influential insofar as they led to a parliamentary enquiry by the British Government. The enquiry formally acknowledged the existence of asbestosis, recognised that it was hazardous to health and concluded that it was irrefutably linked to the prolonged inhalation of asbestos dust. Having established the existence of asbestosis on a medical and judicial basis, the report resulted in the first Asbestos Industry Regulations being published in 1931, which came into effect on 1 March 1932.
The first lawsuits against asbestos manufacturers occurred in 1929. Since then, many lawsuits have been filed against asbestos manufacturers and employers, for neglecting to implement safety measures after the link between asbestos, asbestosis and mesothelioma became known (some reports seem to place this as early as 1898 in modern times). The liability resulting from the sheer number of lawsuits and people affected has reached billions of dollars. The amounts and method of allocating compensation have been the source of many court cases, and government attempts at resolution of existing and future cases.
Some notable persons who have died from lung fibrosis associated with asbestos include:
- Bernie Banton, social justice advocate
- Nellie Kershaw, first person diagnosed with asbestos-related disease, 1924
- John MacDougall, politician
- Steve McQueen, actor
- Theodore Sturgeon, writer
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- Armley asbestos disaster, Spodden Valley asbestos controversy, Turner & Newall
|Wikimedia Commons has media related to Asbestosis.|
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- "Asbestos Toxicity". ATSDR Case Studies in Environmental Medicine. U.S. Department of Health and Human Services.
- "Asbestos health and safety". British Government Health and Safety Executive.
- "Asbestos Exposure". National Cancer Institute, USA.
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