Pleural Plaques and Asbestos

Pleural plaques are by far the most common indication of a prior significant exposure to asbestos. They are characterized by areas of fibrous thickening on the pleura and the outermost lining of the lungs or diaphragm. The condition typically arises 20 to 30 years after asbestos exposure.

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Pleural plaques are benign, meaning they are not cancerous. Furthermore, they cannot become cancerous over time. In nearly every case, there are no symptoms, but some patients describe pain or an uncomfortable grating sensation as they breathe.

They can develop on both layers of the pleura, a thin membrane that surrounds the lungs and aids in breathing. They most commonly develop on the parietal pleura, which lines the inside of the rib cage, but can also affect the visceral pleura, which lines the lungs.

Additionally, pleural plaques can grow on the diaphragm, the primary muscle used for respiration. The plaques can calcify over time, but they do not usually cause long-term health problems.

Causes of Pleural Plaques

Pleural plaques are almost exclusively caused by exposure to asbestos, but having the condition does not necessarily mean you will develop a more serious asbestos-related disease such as asbestosis or mesothelioma.

However, because the presence of plaques suggests a significant past exposure to asbestos, mesothelioma or lung cancer may arise later in life.

Some studies suggest fibrous thickening of the pleura may increase a patient’s risk for developing pleural mesothelioma, but the topic remains controversial. Contradictory studies show a patient’s risk for other asbestos-related conditions is not affected by a diagnosis of pleural plaques.

Instead, they argue doctors should calculate a patient’s risk based on the level and duration of asbestos exposure and how much time has passed since the initial exposure.

How Do They Form?

When people are exposed to asbestos, inhaled fibers can accumulate in the lining of the lungs and irritate the lung tissue. It is believed fibers reach the pleural space through the lymphatic system.

Pleural Macrophages

A leading theory suggests asbestos fibers cause an immune response that summons special lung cells called pleural macrophages. These cells can trigger a chain of events that leads to fibrosis, in which specialized cells replace normal, healthy lung tissue with scar tissue made of collagen fibers.

Quick Fact

In 20 percent of cases, pleural plaques become calcified. As calcium deposits build up in them, the scar tissue hardens. Rarely, calcified pleural plaques can inhibit lung function and cause patients to have trouble breathing.

Pleural Plaque Development

Pleural plaques slowly develop and grow as fibrotic scar tissue accumulates. While doctors traditionally believed they did not affect a patient’s lung function, recent evidence shows they sometimes cause a minimal decrease in total lung capacity and other measures of lung function.

Asbestos-exposed patients with pleural plaques may also develop pleural thickening, which involves more extensive fibrous thickening. Because pleural thickening affects a larger area, it can prevent the lungs from fully expanding and cause shortness of breath.

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Risk, Prevalence and Diagnosis

Often, pleural plaques do not show up until decades after exposure to asbestos. Most experts agree the risk is dose dependent, meaning the risk increases with the level of asbestos exposure and time elapsed since first exposure.

Despite this relationship, low levels of asbestos exposure can still cause pleural plaques to arise.

In a 2013 study in France, doctors screened asbestos-exposed workers using computed tomography (CT) scans.

The study, published in the Journal of the National Cancer Institute, identified pleural plaques in 7.4 percent of patients exposed to asbestos between one and nine years. More than 50 percent of patients with 40 or more years of asbestos exposure developed plaques.

A follow-up study discovered 17 cases of pleural mesothelioma were diagnosed in the cohort between the date of the CT scan and March 31, 2011. The mean age of patients with pleural plaques who later developed mesothelioma was 66.6 years. All mesothelioma diagnoses were linked to occupational asbestos exposure.

Quick Fact

Doctors typically diagnose this condition using a chest X-ray or CT scan. Because it rarely causes symptoms, they usually find it incidentally after performing an imaging scan for an unrelated reason.

Discovery Through X-ray

Most incidences are discovered after an X-ray that displays thickened nodular edges resembling a holly leaf. In certain locations, the condition can be difficult to identify via X-ray. Pleural plaques that are calcified appear more pronounced.

Diagnoses with CT Scan

CT scan is the preferred method for diagnosing this condition, as it can identify plaques anywhere in the chest, even if they are not calcified. In 95 to 100 percent of cases, a CT scan can correctly identify patients who have this condition.

When pleural plaques are first discovered, your health care provider will carefully evaluate your history of asbestos exposure and check for other signs of asbestos-related disease. If you are later diagnosed with an asbestos-related disease, your doctor will create a treatment plan unique to you and your diagnosis.

Treatment and Preventing Further Damage

Because pleural plaques are noncancerous and the majority of patients do not experience a loss in lung function, treatment is not necessary. However, you can prevent further damage by eliminating any pathways of asbestos exposure and by quitting smoking. Your doctor can give you advice to help with smoking cessation.

Although pleural plaques may not place you at a higher risk of developing a more serious asbestos-related disease, the asbestos exposure that caused the plaques does. Therefore you should always notify your doctor if you experience symptoms such as breathlessness, persistent cough, chest pain or coughing up blood. If breathing does become an issue, your doctor can perform a variety of tests and offer treatments and refer you to a specialist.

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Karen Selby joined Asbestos.com in 2009. She is a registered nurse with a background in oncology and thoracic surgery and was the director of a tissue bank before becoming a Patient Advocate at The Mesothelioma Center. Karen has assisted surgeons with thoracic surgeries such as lung resections, lung transplants, pneumonectomies, pleurectomies and wedge resections. She is also a member of the Academy of Oncology Nurse & Patient Navigators. Read More

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Last Modified May 9, 2018
Sources
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    Retrieved from: https://www.atsdr.cdc.gov/csem/csem.asp?csem=29&po=6
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