Pleural Plaque and Thickening

One of the four conditions that can develop from asbestos exposure is pleural plaque and thickening. The others are asbestosis, lung cancer, and mesothelioma (a cancer of the lining that surrounds the lungs, heart or abdominal cavity).

Pleural plaques are the most common condition associated with asbestos exposure; more than 80% of patients with pleural plaques have had a history of asbestos exposure. Pleural plaques develop 20 to 40 years after exposure to asbestos and may occur after low, intermittent exposure. After 20 years, uncalcified pleural plaques can be found in five to 15% of people who were exposed to asbestos at their workplace. Thirty years after the first exposure to asbestos, about a third to one half of people have calcified pleural plaques. A person with pleural plaques may show no other signs of asbestos exposure; however, pleural plaques are present in almost all patients with asbestosis, so the discovery of pleural plaques is a cause for concern.

Pleural plaques are smooth, white, raised irregular areas of tissue formed from collagen bundles arranged in a basket-weave pattern. They almost always appear on the parietal pleura (the outer lining that surrounds the lung). The plaques may contain asbestos fibers and often become calcified as time goes by. They range from small to large, and if calcified can be more easily seen on a chest x-ray.

The larger the plaque, the greater the chance that more asbestos fibers will be found in the patient's lungs, especially if the plaque is calcified. However, the absence of pleural plaques is not a guarantee that asbestos hasn't invaded the lungs; some people with no pleural plaques still have a high concentration of asbestos fibers in the lungs and pleura.

Researchers are not positive how pleural plaques are formed. In the past it was thought that they were the result of scarring that occur when asbestos fibers pierce the visceral pleura (the lining that directly encloses the lung). Now, however, scientists believe the fibers are transported to the parietal pleura via the lymph system and that an immune-system response creates the plaques. The plaques gradually grow over time, even after asbestos exposure has ended. This new theory helps to explain why people with similar levels of asbestos exposure have differing amounts of pleural plaque formation.

Chest x-rays are often used to establish the presence of pleural plaques. In addition, a physician may also order blood work, a high-resolution CT scan, and possibly even a biopsy. Although in themselves pleural plaques are not thought to cause symptoms, if the plaques are big enough, they may slightly affect some lung function tests, so such test are sometimes used in diagnosing pleural plaques. It is possible for other illnesses to cause pleural plaque to form, but if there is no other obvious cause, and a history of asbestos exposure exists, then the assumed cause is the asbestos.

Pleural plaques are non cancerous, and they cannot change into cancer. However, studies have shown that people with pleural plaques run an increased risk of developing lung cancer. There is also evidence that individuals with pleural plaques have a higher risk of developing mesothelioma. Some factors that can increase the risk of cancer are the patient's age, exposure to tobacco or other lung carcinogens and impaired lung function. In addition, when pleural plaques exist in patients more than 10 years after the initial exposure to asbestos, cancer risk is higher.

Diffuse pleural thickening is another condition that may develop from asbestos exposure, though it is also associated with other respiratory diseases. Pleural thickening usually appears approximately 15 years after asbestos exposure. The thickening is believed to be due to inflammation and fibrosis of the visceral pleural lymphatics. It usually extends along the chest wall and involves the visceral pleura instead of just the parietal pleura. In pleural thickening, there is a great deal of fusion of the pleural layers and asbestos fibers. As with pleural plaques, pleural thickening can but does not always cause shortness of breath and impaired lung function.

Pleural thickening in mesothelioma patients occurs when scar tissue builds up around trapped asbestos fibers. This scar tissue, or fibrosis, can make the lungs of mesothelioma victims stiffer and less elastic and can impair breathing function; mesothelioma patients who have pleural thickening may complain of difficulty breathing or chest pain. In some cases, the clinical signs of pleural thickening may be minimal, and for many victims of mesothelioma, pleural thickening is quite progressed by the time it is found. In order to diagnose pleural thickening in mesothelioma cases, the examining doctor will take chest X-rays.

Normally, physicians will treat pleural thickening in mesothelioma patients by attempting to relieve the pressure placed upon the lungs. If it is not treated, the pleural thickening in mesothelioma patients can potentially lead to respiratory and cardiac failure. Physicians may perform a pleurectomy on a patient who has an extreme case of pleural thickening. In this procedure, the doctor removes the thick, fibrous rind characteristic of pleural thickening, which allows the lungs of the mesothelioma victim to expand more easily.

There is no cure for pleural plaque and thickening caused by chronic asbestos exposure, and unless they are reducing lung function, they do not require treatment. Once established, the disease can remain stable or it can get worse, even in the absence of further exposure. As with other asbestos-related diseases, pleural plaques and thickening rarely regress.

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