What are the causes and treatment options for pleural effusion?

Causes of Pleural Effusion

The most common causes of pleural effusion include heart failure (29%), malignancy (26%), pneumonia (16%), tuberculosis (6%), post-surgery (4%), pericardial diseases (4%), and cirrhosis (3%). 1

Classification of Pleural Effusions

Pleural effusions are broadly classified into two categories based on their pathophysiology:

Transudates

Transudates result from systemic factors that alter the hydrostatic or oncotic pressures:

• Heart failure (accounts for >80% of transudates) 1
• Liver cirrhosis (approximately 10% of transudates) 1
• Hypoalbuminemia 1
• Nephrotic syndrome 1
• Atelectasis 1
• End-stage renal failure (prevalence of 24.7% among ESRF patients) 1

Exudates

Exudates result from local factors affecting the pleura:

• Malignancy (lung cancer most common, followed by breast cancer) 1
• Parapneumonic effusions (pneumonia-related) 1
• Tuberculosis 1
• Pulmonary embolism 1
• Rheumatoid arthritis (occurs in 5% of patients) 1
• Systemic lupus erythematosus (affects up to 50% of patients during disease course) 1
• HIV-related causes (Kaposi's sarcoma, parapneumonic effusions, tuberculosis) 1

Special Considerations for Specific Conditions

Malignant Pleural Effusions

• Lung cancer is the leading cause of malignant pleural effusion 1
• Breast cancer is the second most common cause 1
• Lymphoma accounts for approximately 10% of malignant effusions 1
• Multiple myeloma is an infrequent cause (about 6% of cases) with characteristically high pleural protein values 1

Autoimmune Diseases

• Rheumatoid pleural effusions occur more commonly in men despite the disease affecting more women 1
• Pleural fluid in rheumatoid arthritis typically has glucose <1.6 mmol/L (29 mg/dL) 1
• SLE-related effusions may have LE cells in pleural fluid, which is diagnostic 1

HIV-Related Effusions

• Leading causes in HIV patients: Kaposi's sarcoma (33%), parapneumonic effusions (28%), tuberculosis (14%) 1
• Other causes include Pneumocystis carinii pneumonia (10%) and lymphoma (7%) 1

End-Stage Renal Failure

• Causes include fluid overload (61.5%), heart failure (9.6%), and uraemic pleuritis 1
• Unique causes in ESRF patients include urinothorax and peritoneal dialysis-associated pleuro-peritoneal leak 1

Persistent Undiagnosed Effusions

When the cause remains unclear after initial evaluation:

• Reconsider pulmonary embolism and tuberculosis as they are amenable to specific treatment 1
• Many undiagnosed effusions eventually prove to be malignant with sustained observation 1
• Consider thoracoscopy if malignancy is suspected after routine tests have failed 1
• A positive tuberculin skin test with an exudative lymphocytic effusion may justify empirical antituberculous therapy 1

Diagnostic Pitfalls to Avoid

• Misclassification of cardiac and liver transudates as exudates occurs in 25-30% of cases 1
• Pleural fluid ANA testing is not helpful in diagnosing SLE as it mirrors serum levels 1
• Diagnostic bronchoscopy is not indicated unless the patient has hemoptysis or features of bronchial obstruction 1
• Some conditions may cause either transudate or exudate (e.g., non-expansile lung, chylothorax, superior vena cava syndrome) 1

Incidental Pleural Effusions in Cancer Patients

• Incidental findings of pleural effusion on chest radiographs are common (46%) 2
• Asymptomatic effusions in cancer patients can be observed initially 2
• Symptomatic effusions require thoracentesis to determine etiology 2
• CT scan is indicated for better characterization of pleural effusion and underlying lung parenchyma 2

By systematically evaluating the clinical context and pleural fluid characteristics, the cause of pleural effusion can be determined in approximately 85% of cases, allowing for appropriate management strategies to be implemented. 1