Less Common Causes of Pleural Effusion

Introduction to Pleural Effusion Causes

The American Thoracic Society suggests that beyond the common causes of pleural effusion, numerous other important etiologies should be considered in the diagnostic workup of patients with unexplained pleural effusions 1

Rheumatoid arthritis affects the pleura in approximately 5% of patients, with pleural effusions being more common in men despite the disease generally affecting more women 2, 3
The European Respiratory Society notes that rheumatoid pleural effusions can appear serous, turbid, yellow-green, milky, or hemorrhagic; a pleural fluid glucose level below a certain threshold strongly suggests rheumatoid etiology 3
Systemic lupus erythematosus (SLE) causes pleural disease in up to 50% of patients during the course of their illness; the presence of LE cells in pleural fluid is diagnostic 3

The Centers for Disease Control and Prevention states that tuberculosis accounts for approximately 6% of pleural effusions and should always be considered in undiagnosed cases 1, 5
The World Health Organization recommends that pleural fluid smears for acid-fast bacilli are only positive in 10-20% of tuberculous effusions, with culture positive in only 25-50%; adding pleural biopsy histology and culture improves diagnostic sensitivity to about 90% 3

The American College of Chest Physicians suggests that pulmonary embolism is associated with pleural effusions in up to 40% of cases; 80% are exudates and 80% are bloodstained 2, 3
A pleural fluid red blood cell count exceeding a certain threshold suggests malignancy, pulmonary infarction, or trauma 2

The National Institute for Occupational Safety and Health notes that benign asbestos pleural effusion typically occurs within the first two decades after asbestos exposure, with prevalence related to exposure dose 2, 3
These effusions are usually small and asymptomatic with a propensity to be hemorrhagic; they may resolve within 6 months but often leave residual diffuse pleural thickening 3

The American Urological Association states that urinothorax is a rare complication of obstructed kidneys where urine moves through the retroperitoneum into the pleural space 3
Diagnosis is confirmed when pleural fluid creatinine level exceeds serum creatinine; the fluid is typically a transudate with low pH 3

The European Respiratory Society notes that chylothorax appears milky and remains so after centrifugation, unlike empyema which clears 3
End-stage renal failure causes pleural effusions in approximately 24.7% of patients, typically due to fluid overload, heart failure, or uremic pleuritis 1

The American Thoracic Society recommends that in persistently undiagnosed effusions, pulmonary embolism and tuberculosis should be reconsidered as they are amenable to specific treatment 2, 5
Many "undiagnosed" effusions ultimately prove to be malignant with continued observation 2
Approximately 15% of pleural effusions remain undiagnosed despite repeated cytology and pleural biopsy 2

The American College of Chest Physicians notes that misclassification of cardiac and liver transudates as exudates occurs in 25-30% of cases 4, 5
A positive tuberculin skin test with an exudative lymphocytic effusion may justify empirical antituberculous therapy 4