Type of Pleural Effusion Important for Mesothelioma Diagnosis
Pleural effusions are found in 95% of all pleural mesothelioma cases. When a patient presents to a doctor with pleural effusion, however, there are many other diseases which could cause the fluid buildup. There are multiple medical tests that should be conducted by the physician to determine the cause, but when exudative pleural effusion is identifed, the type associated with lung disease, a patient history to assess the possibility of asbestos exposure is important.
Pleural mesothelioma is a form of lung cancer that is almost always caused by asbestos exposure and is most commonly found in the outer lining of the lungs called the mesothelium. Due to the long latency period most cases of mesothelioma are diagnosed 30 years or more after exposure.
A pleural effusion is an accumulation of fluid between the layers of tissue that line the lungs and chest cavity. In healthy adults the body produces pleural fluid in small amounts to lubricate the surfaces of the pleura. This fluid is normally removed by lymphatics in the parietal pleura, which have the capacity to absorb 20 times more fluid than is normally formed. When this capacity is overwhelmed, a pleural effusion develops.
Transudative Effusions vs Exudative Effusions
Determining the cause and type of the pleural effusion is critical in treating the underlying disease as well as determining the appropriate method to clear the fluid from the chest cavity. A lung surrounded by excess fluid for too long may collapse.
There are two types of effusions: transudative effusions and exudative effusions.
Due to elevated pressure or low protein content in the blood vessels, fluid leaks into the pleural space causing transudative effusions. Systemic factors that alter the balance of the formation and absorption of pleural fluid, such as pulmonary embolism and cirrhosis, are the root of transudative effusions. Congestive heart failure is the most common cause of transudative effusions. Other causes include constrictive pericarditis and peritoneal dialysis.
Leaky blood vessels caused by inflammation involving irritation and swelling of the pleura and alterations in local factors that influence the formation and absorption of pleural fluid result in exudative effusions. Exudative pleural effusions are associated with asbestos-related diseases such as mesothelioma and asbestosis. The effusions are often caused by other lung diseases, including lung cancer, lung infections such as tuberculosis and pneumonia, and drug reactions.
According to The Merck Manuals the path to take in diagnosing the disease causing pleural effusion includes using Light’s Criteria. This set of criteria was developed by Dr. Richard Light, Pulmonary Disease Physician and Professor of Medicine at The Vanderbilt Clinic, Nashville, TN, and Director of Pulmonary Disease Program, St Thomas Hospital, Nashville.
The two effusions are differentiated by comparing chemistries in the pleural fluid to those in the blood. Light’s Criteria looks at the ratio of pleural fluid protein to serum protein, the ratio of pleural fluid LDH to serum LDH, and whether the pleural fluid LDH is more than two-thirds the normal upper limit for serum. If the criteria are met then exudative effusion is assumed and additional evaluation is needed to determine the cause of the excess fluid.
Dr. Light agrees with his colleague Gary Lee, Consultant Physician & Senior Lecturer, Osler Chest Unit, Churchill Hospital, Oxford, UK when he says that it is important to go beyond Light’s Criteria and get a detailed history of the patient so the treating physician knows what to do with the exudative identification.
Since X-rays, CT scans and potentially ultrasound have all been performed leading up to confirming that the patient has pleural effusion, and further tests confirm that the effusion is exudative in nature, if the patient’s history reveals exposure to asbestos the doctor may be able to move to tests to eliminate or confirm an asbestos-related disease by checking mesothelial levels.
Injury (inflammation) to the mesothelium triggers events leading to the migration of mesothelial cells from the edge of the lesion towards the wound center, causing an increase in levels. Neoplastic transformation (conversion of a tissue with a normal growth pattern into a malignant tumor) of mesothelial cells gives rise to malignant mesothelioma.
Contact a Specialist
Due to mesothelioma’s relative rarity among the general population, it is recommended that if you are diagnosed with mesothelioma that you be treated by a team of doctors and surgeons led by a mesothelioma specialist. Mesothelioma specialists are aware of the latest research and they are able to develop a more informed treatment plan than would a physician who does not specialize in the disease.