Cause of Pleural Effusion in Nephrotic Syndrome in Children
Pleural effusion in children with nephrotic syndrome occurs primarily due to the combination of decreased oncotic pressure from severe hypoalbuminemia (due to massive proteinuria) and increased hydrostatic pressure from salt and water retention, resulting in fluid accumulation in the pleural space. 1
Primary Pathophysiological Mechanisms
The development of pleural effusion in pediatric nephrotic syndrome follows a dual mechanism:
Low oncotic pressure: Massive proteinuria (typically >3.5 g/day in adults, proportionally less in children) leads to severe hypoalbuminemia (usually <25 g/L), which reduces the plasma oncotic pressure that normally keeps fluid within the vascular space. 1
Increased hydrostatic pressure: Salt retention by the kidneys increases total body sodium and water, elevating hydrostatic pressure in the capillaries and promoting fluid extravasation into third spaces including the pleural cavity. 1
Fluid overload: The combination of these mechanisms results in generalized edema, which manifests as ascites, peripheral edema, pericardial effusions, and pleural effusions. 1
Clinical Characteristics
The pleural fluid in nephrotic syndrome has specific features:
Usually transudative: The effusion is typically transudative due to the oncotic-hydrostatic imbalance, though it may occasionally appear exudative depending on the specific pathophysiological mechanisms at play. 1
Often bilateral: Unlike infectious causes, nephrotic syndrome can produce bilateral effusions due to the systemic nature of the fluid retention. 1
Associated with other signs of fluid overload: Physical examination typically reveals ascites, peripheral edema, and potentially pericardial effusions alongside the pleural effusion. 1
Important Clinical Context
Understanding the broader picture of nephrotic syndrome helps contextualize the pleural effusion:
Hypoalbuminemia threshold: Edema formation, including pleural effusions, typically occurs when serum albumin falls below 25 g/L, though individual variation exists. 2
Complications beyond fluid retention: Children with nephrotic syndrome face additional risks including thromboembolism, serious infections (cellulitis, spontaneous bacterial peritonitis), and accelerated cardiovascular disease. 1, 3
Rare variant - chylothorax: In exceptional cases, nephrotic syndrome can cause chylous ascites that leads to chylothorax via transdiaphragmatic shunting, presenting as a milky pleural effusion. 4
Management Implications
Treatment targets the underlying nephrotic syndrome rather than the effusion itself:
Primary treatment: Management focuses on treating fluid overload and hypoalbuminemia through direct management of the underlying nephrotic syndrome with immunosuppressive therapy (corticosteroids as first-line, with cyclosporin or other agents for resistant cases). 1
Supportive measures: Salt restriction, fluid management using concentrated high-calorie formulas to meet nutritional needs while limiting volume, and judicious use of diuretics help control edema. 1
Albumin infusions: Some centers use regular albumin infusions (1-4 g/kg/day) to temporarily improve oncotic pressure, though practice varies considerably between institutions. 1
Key Clinical Pitfalls
Don't assume infection: Unlike the more common parapneumonic effusions in children, nephrotic syndrome produces sterile effusions that do not require antibiotics unless secondary infection is documented. 1
Avoid unnecessary drainage: Small to moderate pleural effusions in nephrotic syndrome typically resolve with treatment of the underlying condition and do not require thoracentesis unless causing significant respiratory compromise. 1
Monitor for complications: The presence of pleural effusion indicates significant disease activity and warrants close monitoring for thrombotic complications (renal vein thrombosis, pulmonary embolism) and infections. 1, 3