What is asbestosis?
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.
What are symptoms and signs of asbestosis?
The clinical symptoms usually include slowly progressing shortness of breath and cough, often 20 to 40 years after exposure to asbestos. 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").
What tests and studies are used to evaluate asbestosis?
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 obstruction 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 on 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 is 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.
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