Asbestos Exposure Disorders

Asbestos is a family of naturally occurring silica compounds (similar to, but not the same as, the silica of window glass and computer chips) found in rocks and soil. These substances form fibers with varying shapes and sizes and are found throughout the earth.

There are three commonly available types of asbestos include:

1. Chrysotile (white asbestos)
2. Amosite (brown asbestos)
3. Crocidolite (blue asbestos)

Another type of lung disease that is linked to asbestos exposure involves the lining of the lungs, called the pleura. The harmless disease of the pleura is often the only manifestation of asbestos exposure. Several different changes can occur in the pleura with asbestos exposure. Pleural plaques may develop from fibers that migrate out to the outside edge of the lungs and cause scarring of the pleura. Pleural "calcification" may occur from calcium deposits in areas of prior damage.

Fluid may accumulate around the lung. This fluid collection called a pleural effusion, can be the first sign of asbestos-related disease. Often, these fluid collections have no associated symptoms, resolve on their own, and recur sporadically. However, some patients may experience pain or bleeding around their lungs. "Diffuse pleural thickening," which means a generalized thickening of the lining of the lung, can occur as well. The thickened pleura may form a peel of scar tissue and even affect the lung's ability to expand. This condition may cause significant shortness of breath. Diffuse pleural thickening is considered a later-onset consequence of repeated fluid accumulations.

Chrysotile is the only form of asbestos that is currently in production today. Despite their association with lung cancer, chrysotile products are still used in 60 industrialized and developing countries, according to the industry-sponsored Asbestos Institute. Chrysotile is still being used in cement building materials (90% of the world's production of chrysotile), friction materials, gaskets, and certain plastics.

Although the asbestos industry proclaims the "safety" of chrysotile fibers, which are now embedded in less "friable" and "dusty" products, little is known about the long-term effects of current asbestos products because of the long delay to the development of disease. Despite their potential health risks, the durability and cheapness of these products continue to attract commercial applications. Asbestosis remains a significant clinical problem even after marked reductions in on-the-job exposure to asbestos. Again, this is due to the long period between exposure and the onset of the disease.

Lung disease from asbestos exposure can be divided into three main types:

1. Asbestosis is a process of widespread scarring of the lungs.
2. The disease of the lining of the lungs called the pleura, has a variety of signs and symptoms and is the result of inflammation and the hardening (calcification) and/or thickening of the lining tissue.
3. Lung cancer, either of the internal portions of the lungs or the outer lining (pleura).

All of the commonly available commercial forms of asbestos have been linked to cancerous and non-cancerous lung diseases.

Depending on their shape and size, asbestos fibers deposit in different areas of the lung. Fibers less than 3 mm easily move into the lung tissue and the lining surrounding the lung (pleura). Long fibers, greater than 5 mm (1/5 inch), cannot be completely broken down by scavenger cells (macrophages) and remain in the lung tissue. These asbestos fibers can cause inflammation. Substances damaging to the lungs are then released by the cells of inflammation that are responding to the foreign asbestos material. The persistence of these long fibers in the lung tissue and the resulting inflammation seem to initiate the process of cancer formation.

As inflammation and damage to the tissue around the asbestos fibers continue, the resulting scarring can extend from the small airways to the larger airways and the tiny air sacs (alveoli) at the end of the airways. Some of these fibers can move to the surface of the lung where they form plaques (white-gray regions of scarred tissue) in the tissue lining of the lung (pleura). In severe cases of asbestosis, scarring of both the lung and its lining tissue can occur.

Asbestos-related lung disease occurred at very high rates toward the middle of the 20th century when patients who were exposed decades earlier to asbestos eventually developed the disease. British asbestos workers were among the first who were observed to have lung cancer related to asbestos.

About 125 million people worldwide are exposed to asbestos in the workplace, and most people with lung disease from asbestos exposure were exposed to it from:

• Mines
• Mills
• Factories
• Homes with asbestos, either in the process of carrying, installing, or removing asbestos or while cleaning items laden with asbestos dust

Some workers have been exposed to high concentrations of asbestos in:

• Automotive repair
• Boiler making
• Construction
• Pipefitting
• Launderers of asbestos-containing clothing

Continuing sources of exposure are asbestos removal and general construction industries. The delay between exposure to asbestos and the development of cancer can be anywhere from 10 to 40 or more years.

Despite not using asbestos in construction materials for the last 30 years, the number of deaths from asbestosis has increased over the past two decades. A 2009 study to assess the incidence of asbestos-related deaths concluded that the death rate is not expected to decrease sharply in the next 10 to 15 years. Each year in the US, asbestos exposure kills about 12,000 to 15,000 people. Some World Trade Center rescue and recovery workers have asbestos exposure to lung disease.

There are two major groups of fibers, the amphiboles, and chrysotile fibers, and all three have been associated with cancerous and non-cancerous lung disease.

1. Chrysotile (white asbestos), also called "Serpentine" fibers, are long and curled.
2. The amphiboles, long straight fibers (including actinolite, amosite, anthrophyllite, crocidolite, and tremolite) are much more likely to cause cancer of the lining of the lung (mesothelioma) and scarring of the lining of the lung (pleural fibrosis). Either group of fibers can cause disease of the lung, such as asbestosis.

The risk of developing asbestos-related lung cancer varies between fiber types. Studies of groups of patients exposed to chrysotile fibers show only a moderate increase in risk. On the other hand, exposure to amphibole fibers or both types of fibers increases the risk of lung cancer two-fold. Although the Occupational Safety and Health Administration (OSHA) has a standard for workplace exposure to asbestos (0.2 fibers/milliliter of air), there is debate over what constitutes a safe level of exposure. While some believe the asbestos-related disease is a "threshold phenomenon," which requires a certain level of exposure for the disease to occur, others believe there is no safe level of asbestos.

In most buildings, asbestos does not become airborne. However, surfaces that are damaged or disturbed can cause asbestos to become inhalable. High concentrations can occur after cutting, sanding, or remodeling asbestos-containing materials.

Reducing asbestos exposure involves either the removal or sealing of asbestos-containing materials. Inexperienced attempts to remove asbestos can release dangerous levels of the fibers.

Asbestos has been used frequently in a variety of building materials for insulation and as a fire retardant, and in brake pads in cars. Today, it is found most commonly in older homes - in pipes, furnaces, roof shingles, millboards, textured paints, coating materials, and floor tiles.

Asbestosis is a process of lung tissue scarring caused by asbestos fibers. Because many other diseases also lead to lung scarring, other causes must be excluded first when a patient is found to have lung scarring (pulmonary fibrosis). Patients with particular X-ray findings or biopsy results must also have a remote history of asbestos exposure and a characteristically delayed development of the condition in considering asbestosis as a diagnosis. Smoking appears to increase the frequency and/or the rate of progression of asbestosis, possibly by preventing the efficient elimination of inhaled fibers from the airways.

Symptoms and signs of asbestosis

• The clinical symptoms usually include slowly progressing shortness of breath and cough, often 20 to 40 years after asbestos exposure.
• Breathlessness advances throughout the disease, even without further asbestos inhalation.
• In the absence of cigarette smoking, sputum (mucus coughed up from the lungs) production and wheezing are uncommon.
• The exception is workers who have been exposed to very high concentrations of asbestos fibers. Those workers may also develop symptoms as soon as 10 years after exposure.
• Other indications of asbestosis include abnormal lung sounds on examination, changes in the ends of the fingers and toes ("clubbing"), a blue tinge to the fingers or lips ("cyanosis"), and failure of the right side of the heart ("cor pulmonale").

Breathing abnormalities can be identified with lung function tests (pulmonary function tests or PFTs) or exercise tests that are performed at specialized laboratories. Asbestosis can produce both obstructions of airflow and restriction of lung inflation. In addition, the disease can affect the ability to transfer oxygen into the blood. With advanced disease, patients may have markedly reduced blood oxygen at rest and may need supplementary oxygen.

X-ray abnormalities include thickening of the lining of the lungs and tiny lines marking the lower portions of the lungs. However, up to 20% of patients have completely normal-appearing chest X-rays. These patients may demonstrate more subtle changes in computerized X-ray studies (computerized tomography, or CT scans). Up to 30% of patients with a normal chest X-ray who have been exposed to asbestos will have an abnormal high-resolution (high definition) CT. The CT scan may be very useful in separating true asbestosis from other conditions that may have similar findings. However, even a CT scan may not identify disease of the lining of the lung (pleural disease) in patients with asbestosis. The proper role of CT scanning has not been fully established.

Laboratory testing studies may be abnormal (certain antibodies and markers of inflammation), but they do not specifically suggest asbestosis.

Occasionally, a biopsy and microscopic examination of the lung are used to diagnose asbestosis. Under microscopic examination, certain coated fibers (asbestos bodies) can be seen in association with a pattern of scarring. The amount of both coated and uncoated (transparent) asbestos has been linked to the severity of asbestosis. Because other particles may resemble asbestos, a conclusive identification may require scanning electron microscopy. Currently, detection of asbestos fibers in the lung tissue and fluids (sputum, secretions) can be used to make the diagnosis, along with a history of asbestos exposure and characteristic X-ray or CT results.

The currently available commercial form of asbestos, chrysotile, does not form asbestos bodies as easily as previously used fibers.

Patients with asbestosis, like others with chronic lung disease, are at a higher risk of serious infection, low oxygen levels in the blood, and heart failure. These patients also may not recover as quickly from viral and bacterial infections. In addition, they may be at increased risk for certain fungal and unusual infections that take advantage of diseased or scarred lung tissue. The medical management of these patients should focus special attention on preventing and rapidly treating these infections. Flu and pneumococcal vaccinations are a part of routine care for these patients. There is, however, no treatment or cure for asbestosis. In particular, steroid and immune-based therapies have not been shown to benefit these patients.

Other key elements in treating patients with asbestosis are smoking cessation, early detection of worsening disease or cancer, and avoidance of further asbestos exposure. Supplemental oxygen during exercise or at rest (depending on the need) may be provided to improve daily function.

Although exposure to asbestos alone can lead to lung cancer, the risk increases dramatically in smokers of cigarettes or other forms of tobacco.

• In nonsmokers who have been exposed to asbestos, the risk of lung cancer is five times that of unexposed workers.
• Smokers who are exposed to asbestos have a 50 to 84 times greater risk of lung cancer, according to the Agency for Toxic Substances Disease Registry.

Lung cancer in asbestos-exposed and unexposed individuals is similar in both the type of cancer and its signs and symptoms. The link between cigarette smoking, asbestos, and cancer of the lung itself does not apply to cancer of the lining of the lung (malignant mesothelioma ). Diagnosis and treatment of lung cancer is a complex topic and a pulmonary specialist should be involved in the workup of suspected lung cancer.

Asbestos is the only known risk factor for malignant mesothelioma, a cancer that affects the tissue lining the lung (pleura) or abdomen (peritoneum). Malignant mesothelioma is not associated with cigarette smoking but is strongly linked with the degree of asbestos exposure. However, 20% to 40% of patients with malignant mesothelioma have no prior asbestos exposure. In malignant mesothelioma, there is a very long duration between exposure and the onset of the disease, usually greater than 30 years.

Other malignancies have been linked to asbestos, including:

• Cancers of the voice box (larynx)
• Upper throat (oropharynx) cancer
• Kidney cancer
• Esophagus cancer
• Gallbladder cancer

The basic principle for asbestos is to leave material that is in good condition alone. Periodic inspection and maintenance by an expert in asbestos abatement should be undertaken for areas with sealed or contained asbestos. Local health, environmental, and building safety officials are good sources for local and state regulations on asbestos handling, disposal, and certified workers. If you discover even a very small amount of asbestos in your building, contact a professional for repair, removal, or remodeling.