Asbestosis
Asbestosis is widespread scarring of lung tissue caused by breathing asbestos dust.
Asbestos is composed of fibrous mineral silicates of different chemical compositions. When inhaled, asbestos fibers settle deep in the lungs, causing scars. Asbestos inhalation also can cause the two layers of membrane covering the lungs (the pleura) to thicken; these thickenings are called pleural plaques. These plaques do not become cancerous.
Inhaling asbestos fibers can occasionally cause fluid to accumulate in the space between the two pleural layers of the lungs (pleural space); this is called a noncancerous (benign) asbestos effusion.
Asbestos also causes cancer in the pleura, called mesothelioma, or in the membranes of the abdomen, called peritoneal mesothelioma. In the United States, asbestos is the only known cause of cancerous (malignant) mesothelioma. Smoking is not a cause of cancerous mesothelioma. Mesotheliomas most commonly appear after exposure to crocidolite, one of four types of asbestos. Amosite, another type, also causes mesotheliomas. Chrysotile probably causes fewer cases of mesotheliomas than other types, but chrysotile is often contaminated with tremolite, which does. Mesotheliomas usually develop 30 to 40 years after exposure and can occur after low exposure.
Asbestos can also cause lung cancer. Lung cancer from asbestos is related in part to the level of exposure to asbestos fibers; however, among people with asbestosis, lung cancer occurs most commonly in those who also smoke cigarettes, particularly those who smoke more than a pack a day (see Section 4, Chapter 57).
Although the general public has become alarmed about the risks of asbestos, most nonoccupationally exposed people are at extremely low risk of developing asbestos-related lung disease. The asbestos must be broken into tiny pieces to be inhaled into the lungs. Workers who demolish buildings that have insulation containing asbestos are at increased risk. People who regularly work with asbestos are at greatest risk of developing lung disease. The more a person is exposed to asbestos fibers, the greater the risk of developing an asbestos-related disease.
Symptoms
Symptoms of asbestosis appear gradually only after large areas of the lung become scarred. The scarring causes the lungs to lose their elasticity. The first symptoms are a mild shortness of breath and a decreased ability to exercise. Smokers who have chronic bronchitis along with asbestosis may cough and wheeze. Gradually, breathing becomes more and more difficult. In about 15% of people with asbestosis, severe shortness of breath and respiratory failure develop.
A person with noncancerous asbestos effusion may have difficulty in breathing because of fluid accumulation. Pleural plaques cause only a mild breathing difficulty that results from stiffness of the chest wall. Persistent pain in the chest and shortness of breath are the most common symptoms caused by mesothelioma.
Diagnosis
Usually, the person with asbestosis has abnormal lung function, and a doctor listening with a stethoscope placed over the lungs can hear abnormal sounds called crackles. In a person who has a history of exposure to asbestos, a doctor sometimes can diagnose asbestosis with a chest x-ray or a chest computed tomography (CT) that shows characteristic changes. Pleural plaques that develop in many people with exposure to asbestos often contain calcium, which makes them easy to see on chest x-rays and CT. A lung biopsy is rarely needed to make the diagnosis.
If a tumor of the pleura is found on x-ray, a doctor must perform a biopsy (remove a small piece of pleura and examine it under a microscope) to determine if it is cancerous. Fluid around the lungs may be removed with a needle and analyzed for cancer cells (a procedure called thoracentesis). However, thoracentesis is not usually as accurate as performing a pleural biopsy. If a chest x-ray reveals something that looks like a tumor, there is a good possibility that the area is a primary lung cancer and should be evaluated fully.
Prevention and Treatment
Diseases caused by asbestos inhalation can be prevented by minimizing asbestos dust and fibers in the workplace. Because industries that use asbestos have improved dust control, fewer people develop asbestosis today, but mesotheliomas are still occurring in people who were exposed as many as 40 years ago. Asbestos in the home should be removed by workers trained in safe removal techniques. Smokers who have been in contact with asbestos can reduce their risk of lung cancer by giving up smoking and should probably have a chest x-ray annually.
Most treatments for asbestosis ease symptoms--for example, oxygen therapy relieves shortness of breath. Draining fluid from around the lungs using a procedure called thoracentesis also may make breathing easier. Occasionally, lung transplantation has been successful in treating asbestosis.
Mesotheliomas are invariably fatal; most people with mesotheliomas die within 1 to 4 years of diagnosis. Chemotherapy and radiation therapy do not work well, and surgical removal of the tumor does not cure the cancer. Other treatment is focused on controlling pain and shortness of breath, in an effort to preserve as much quality-of-life as possible (see Section 1, Chapter 8).
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