What is the most common cause of bilateral pleural effusion?

Most Common Cause of Bilateral Pleural Effusion

Heart failure is the most common cause of bilateral pleural effusion, accounting for approximately 80% of transudative pleural effusions and 29% of all pleural effusions. 1

Causes of Bilateral Pleural Effusions

Transudative Causes

• Heart failure is the predominant cause of bilateral transudative effusions 1
• Liver cirrhosis accounts for approximately 10% of transudative effusions 1
• End-stage renal failure has a prevalence of 24.7% among ESRF patients and commonly presents with bilateral effusions 1
• Other causes include hypoalbuminemia, nephrotic syndrome, and atelectasis 1

Exudative Causes

• Malignancy (particularly lung cancer) is a leading cause of exudative pleural effusions 1, 2
• Parapneumonic effusions and tuberculosis can present bilaterally, though they are more commonly unilateral 3, 1
• Pulmonary embolism can cause bilateral effusions, though this is less common 3
• Autoimmune conditions like rheumatoid arthritis (5% of patients) and systemic lupus erythematosus (up to 50% of patients during disease course) can cause bilateral exudative effusions 1

Clinical Presentation and Diagnostic Approach

Clinical Features Suggesting Heart Failure as Cause

• In patients with known heart failure and bilateral effusions, thoracentesis may not be necessary if clinical features strongly suggest heart failure 3
• Thoracic and cardiac ultrasound findings consistent with heart failure can support the diagnosis 3
• N-terminal pro-brain natriuretic peptide (NT-BNP) levels >1500 μg/mL in serum or pleural fluid can accurately diagnose heart failure as the cause 1

Clinical Features Suggesting Alternative Diagnoses

• Weight loss, chest pain, fevers, elevated white cell count, or elevated C-reactive peptide suggest an alternative diagnosis to heart failure 3
• CT evidence of malignant pleural disease or pleural infection should prompt further investigation 3
• Bilateral effusions may indicate tuberculosis in certain clinical contexts 3

Diagnostic Algorithm

1. Initial Assessment:

   • Determine if effusion is likely transudative or exudative based on clinical presentation 3
   • Small bilateral effusions in patients with decompensated heart failure, cirrhosis, or kidney failure are likely transudative and may not require diagnostic thoracentesis 4

2. Imaging:

   • Chest radiography to determine size and laterality 4
   • Point-of-care ultrasound to detect small effusions and features suggesting complicated effusion or malignancy 4
   • CT chest if other causes of dyspnea need to be excluded or to evaluate for complicated parapneumonic or malignant effusion 4

3. Laboratory Testing:

   • If thoracentesis is performed, apply Light's criteria to differentiate exudates from transudates 1
   • Consider serum-effusion albumin gradient >1.2 g/dL to reclassify an effusion as a transudate when heart failure is suspected but Light's criteria suggest an exudate 1
   • Measure NT-proBNP in pleural fluid to identify effusions due to heart failure that meet exudative criteria 5

Clinical Pearls and Pitfalls

• Misclassification of cardiac and liver transudates as exudates occurs in 25-30% of cases 1, 5
• While heart failure typically causes bilateral effusions, unilateral effusions can occur in 41% of cases with acute decompensated heart failure 3
• In a study from Nepal, 87.5% of patients with congestive heart failure had bilateral effusions, confirming it as the most common cause of bilateral pleural effusion 6
• Bilateral effusions may indicate a systemic disease process rather than a localized pulmonary or pleural pathology 3, 7