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Pleural effusion is a manifestation of several diseases, and its most common symptom at clinical presentation is difficulty of breathing. Other associated symptoms and physical examination findings are specifically related to a disease entity. For example, an individual with heart failure, which is a common etiology of pleural effusion, may also present with both difficulty of breathing at night or while lying down as well as progressive swelling of the lower extremities. The etiology of pleural effusion includes diseases such as liver cirrhosis, pulmonary embolism, nephrotic syndrome, superior vena cava obstruction, myxedema, cancer, and several infectious or autoimmune diseases. Pleural effusion may be induced on occasion from radiotherapy,iatrogenic injury from abdominal surgery or transplantation of liver, lung, or heart, or several drugs including nitrofurantoin, dantrolene, methysergide, bromocriptine, procarbazine, and amiodarone.
The initial step in identifying the etiology of pleural effusion is to determine whether it is a transudative pleural effusion or an exudative pleural effusion. Both are distinguished by measurement of protein levels and lactate dehydrogenase in the pleural fluid. Transudative pleural effusion occurs when physiological alteration in the formation and absorption of pleural fluid is due to systemic factors, such as increased hydrostatic pressure or decreased oncotic pressure. Exudative pleural effusion occurs when physiological alteration in the formation and absorption of pleural fluid is due to local factors, such as inflammation of the pleura or decreased lymphatic drainage.
In many developed countries, leading etiologies of transudative pleural effusion are left ventricular heart failure and liver cirrhosis. Leading etiologies of exudative pleural effusion are bacterial pneumonia, cancer, pulmonary embolism, and viral infection. Although relatively uncommon in the developed countries, tuberculosis is the most common cause of exudative pleural effusion in many parts of the world. The most common cancers that cause pleural effusion are lung cancer, breast cancer, and lymphoma.
Confirmatory diagnostic procedures and therapeutic management must be tailored to the specific etiology of pleural effusion. The goal of therapeutic management is cure, if not symptomatic relief. For example, in a patient presenting with pleural effusion suspected to be secondary to tuberculosis, the diagnosis can be established by high tuberculosis markers or positive culture in the pleural fluid, and the treatment is a combination therapy of isoniazid, rifampicin, pyrazinamide, and ethambutol. In pleural effusion secondary to cancer, diagnosis can be initially established via cytology of the pleural fluid. The treatment is for symptomatic relief only with therapeutic thoracentesis, because chemotherapy does not cure pleural effusion.