Pleural effusion can be caused by various diseases, with difficulty breathing being the most common symptom. Identifying whether it is transudative or exudative is the first step in determining the etiology. Treatment is tailored to the specific cause, with the goal of cure or symptomatic relief.
Pleural effusion is a manifestation of several diseases and its most common symptom at clinical presentation is difficulty breathing. Other associated symptoms and physical examination findings are specifically related to an entity of the disease. For example, an individual with heart failure, which is a common etiology of pleural effusion, may also have both nocturnal or lying-down breathing difficulties and 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 various infectious or autoimmune diseases. Pleural effusion may occasionally be induced by radiation therapy, iatrogenic injury from abdominal surgery or liver, lung, or heart transplantation, or several drugs including nitrofurantoin, dantrolene, methysergide, bromocriptine, procarbazine, and amiodarone.
The first step in identifying the etiology of the pleural effusion is to determine whether it is a transudative pleural effusion or an exudative pleural effusion. Both are distinguished by the measurement of protein and lactate dehydrogenase levels in the pleural fluid. Transudative pleural effusion occurs when the 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 the physiological alteration of 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, the main etiologies of transudative pleural effusion are left ventricular heart failure and cirrhosis of the liver. The main etiologies of exudative pleural effusion are bacterial pneumonia, cancer, pulmonary embolism, and viral infection. Although relatively rare in 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 effusions are lung cancer, breast cancer, and lymphoma.
Confirmatory diagnostic procedures and therapeutic management must be tailored to the specific etiology of the pleural effusion. The goal of therapeutic management is cure, if not symptomatic relief. For example, in a patient presenting with a pleural effusion suspected to be secondary to tuberculosis, the diagnosis may be established by elevated tuberculosis markers or a positive culture in the pleural fluid, and treatment is a combination therapy of isoniazid, rifampicin, pyrazinamide, and ethambutol . In pleural effusion secondary to cancer, the diagnosis can initially be established by cytology of the pleural fluid. Treatment is for symptomatic relief with therapeutic thoracentesis only, because chemotherapy does not cure the pleural effusion.
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