What are the causes of serositis presenting as pleural effusion and ascites in children?

Causes of Serositis (Pleural Effusion with Ascites) in Children

When a child presents with combined pleural effusion and ascites (serositis), malignancy—particularly hematologic malignancies—must be the primary consideration, especially if the fluid is hemorrhagic, followed by systemic autoimmune diseases like systemic lupus erythematosus (SLE), with infectious causes typically producing isolated rather than combined serous effusions. 1

Primary Diagnostic Categories

Malignancy (Highest Priority)

• Hematologic malignancies are the predominant pediatric cancers causing serositis, with most malignant effusions being blood-stained in children 1
• Suspect malignancy when there is:
  • Absence of acute fever or pneumonia 1
  • Evidence of mediastinal mass or lymphadenopathy 1
  • Hemorrhagic pleural fluid and ascites without trauma history 1
• Send cytological examination to the hematology laboratory first for cytospin analysis, then forward to cytology if non-hematologic malignant cells are identified 1

Autoimmune/Connective Tissue Disorders

• Systemic lupus erythematosus (SLE) is a critical cause of polyserositis in children, with approximately 16% of SLE patients having pleural or pericardial involvement, though peritoneal involvement is extremely rare 2
• SLE can present with ascites as the first manifestation, characterized by:
  • Abdominal distension and pain 2
  • Decreased serum complement levels 2
  • Positive anti-nuclear antibodies, anti-Sm antibodies, and anti-SS-A antibodies 2
  • Immune complex vasculitis with depressed pleural and peritoneal fluid complement levels 3
• Antinuclear antibodies' positivity in serum is significantly associated with autoimmune disease as the cause of polyserositis 4
• Familial Mediterranean Fever (FMF) causes recurrent polyserositis affecting pleura, peritoneum, and synovial membranes, though typically presents with recurrent episodes rather than persistent effusions 5

Infectious Causes (Usually Isolated, Not Combined)

• Infectious etiologies rarely cause combined pleural effusion and ascites; they typically produce isolated pleural effusions 6
• When infection does cause pleural effusion in children:
  • Streptococcus pneumoniae is the predominant pathogen (75% of culture-negative cases by PCR) 6
  • Staphylococcus aureus is particularly common in developing countries and in infants under 6 months 6, 7
  • Mycobacterium tuberculosis can cause tuberculous empyema (up to 6% of empyema cases worldwide), which may rarely involve peritoneum 6
  • Gram-negative organisms (Klebsiella, Pseudomonas aeruginosa) are more common in developing countries and associated with protein-energy malnutrition 6

Post-Surgical and Traumatic Causes

• Trauma is a recognized cause producing hemorrhagic fluid in both pleural and peritoneal spaces 1
• Post-cardiothoracic surgery can result in hemorrhagic effusions and ascites 6, 1
• Chronic graft-versus-host disease (cGVHD) rarely manifests as serositis with ascites and pleural effusion, typically in post-transplant patients 8

Critical Diagnostic Approach

Immediate Fluid Analysis

• Send aspirated fluid for differential cell count immediately to distinguish:
  • Neutrophil-predominant → infection 1
  • Lymphocyte-predominant → tuberculosis or malignancy 1
• Perform Gram stain and culture for aerobic/anaerobic organisms 1
• Measure pleural fluid LDH, protein, pH, and glucose:
  • Increased LDH significantly associated with neoplasm 4
  • Decreased pH and glucose suggest fibropurulent stage of infection 9
• Check adenosine deaminase levels: elevated levels significantly associated with tuberculosis or autoimmune disease 4

Imaging Evaluation

• Perform CT chest scan when malignancy needs to be excluded, particularly to evaluate for lymphoma or mediastinal masses 1
• Abdominal CT may demonstrate bowel wall thickening ("target sign" or "double-track sign") in lupus peritonitis 2

Critical Clinical Pitfalls to Avoid

Procedural Safety

• DO NOT perform large volume thoracentesis or use general anesthesia/sedation when superior mediastinal obstruction from malignancy is suspected—this carries significant mortality risk 1
• Limit diagnostic taps to 5 mL in suspected mediastinal obstruction 1

Diagnostic Errors

• DO NOT assume all hemorrhagic effusions are traumatic; malignancy and infection must be systematically excluded 1
• DO NOT dismiss the possibility of SLE in children, even though peritoneal involvement is rare—it can be the first manifestation 2
• In children with known cancer history, polyserositis may represent cancer recurrence (9 of 14 patients in one series) 4

Treatment Considerations

• SLE-related serositis may respond poorly to corticosteroids alone and often requires addition of immunosuppressive agents 3
• Colchicine is definitive treatment for FMF-related serositis 5
• Neoplasm is the most common diagnosis in polyserositis cases (nearly one-third), followed by infectious and autoimmune diseases, with unknown etiology in over one-third of cases 4