Description

Types: transudate (low protein/low specific gravity) and exudate (high protein and cellular debris)

• Transudate: Congestive heart failure (CHF): 40%
• Exudates: pneumonia 25%, malignancy 15%, and pulmonary embolism (PE) 10%
  • Malignant: lung cancer and metastases of breast, ovary, and lymphoma

Epidemiology

Incidence
Estimated 1.5 million cases per year in the United States; CHF: 500,000; pneumonia: 300,000; malignancy: 150,000; PE: 150,000; cirrhosis: 150,000; tuberculosis (TB): 2,500; pancreatitis: 20,000; collagen vascular disease: 6,000

• Estimated 320 cases per 100,000 people in industrialized countries; in hospitalized patients with AIDS, prevalence is 7–27%.
• No gender predilection: ~2/3 of malignant pleural effusions occur in women.

Etiology and Pathophysiology

• Pleural fluid formation exceeds pleural fluid absorption.
• Transudates result from imbalances in hydrostatic and oncotic forces.
  • Increase in hydrostatic and/or low oncotic pressures; increase in pleural capillary permeability; lymphatic obstruction or impaired drainage; movement of fluid from the peritoneal or retroperitoneal space
• Transudates
  • CHF: 40% of transudative effusions; 80% bilateral; constrictive pericarditis, atelectasis; superior vena cava syndrome
  • Cirrhosis (hepatic hydrothorax); nephrotic syndrome, hypoalbuminemia; myxedema
  • Urinothorax, central line misplacement; peritoneal dialysis
  • Dressler syndrome (postmyocardial infarction syndrome)
  • Yellow nail syndrome: yellow nails, lymphedema and pleural effusion
• Exudates
  • Lung parenchyma infection, bacterial (parapneumonic, tuberculous pleurisy), fungal, viral, parasitic (amebiasis, Echinococcus)
  • Cancer: lung cancer, metastases (breast, lymphoma, ovaries), mesothelioma
  • PE: 25% of PEs are transudate.
  • Collagen vascular disease: rheumatoid arthritis, systemic lupus erythematosus (SLE), Wegener granulomatosis, sarcoidosis, Churg-Strauss
  • GI: pancreatitis, esophageal rupture, abdominal abscess, after liver transplant; chylothorax: thoracic duct tear, malignancy
  • Hemothorax: trauma, PE, malignancy, coagulopathy, aortic aneurysm
  • Others: after coronary artery bypass graft; uremia, asbestos exposure, radiation; drug induced:
    • Drugs: nitrofurantoin, bromocriptine, amiodarone, procarbazine, hydralazine, procainamide, quinidine, methotrexate, methysergide, interleukin-2, mitomycin, practolol, minoxidil, bleomycin, cyclophosphamide, dantrolene, valproic acid, sulfasalazine, minocycline, acebutolol, phenytoin, practolol, minoxidil, methysergide, L-tryptophan, dasatinib.
  • Meigs syndrome; yellow nail syndrome; ovarian stimulation syndrome; lymphangiomatosis; acute respiratory distress syndrome (ARDS)
  • Chylothorax: thoracic duct tear, malignancy, associated with lymphoma

Risk Factors

• Occupational exposures/drugs
• PE, TB, bacterial pneumonias
• Opportunistic infections (in HIV patients when CD4 count is <150 cells/μL)

Commonly Associated Conditions

Hypoproteinemia, heart failure, cirrhosis