Can malignant ascites be complicated by Spontaneous Bacterial Peritonitis (SBP)?

Malignant Ascites and Spontaneous Bacterial Peritonitis

Yes, malignant ascites can be complicated by spontaneous bacterial peritonitis (SBP), although this is not as commonly recognized as SBP in cirrhotic ascites. 1

Definition and Diagnosis of SBP

SBP is defined as a bacterial infection of ascitic fluid without an evident intra-abdominal surgically treatable source of infection. The diagnosis is established when:

• Ascitic fluid neutrophil count is >250 cells/mm³ in the absence of an intra-abdominal surgically treatable source 2
• This diagnostic threshold has the greatest sensitivity, though a cut-off of 500 neutrophils/mm³ offers greater specificity 2

Pathophysiology of SBP in Different Types of Ascites

Cirrhotic Ascites

• Most commonly associated with SBP (prevalence of 1.5-3.5% in outpatients and approximately 10% in hospitalized patients) 2
• Bacterial translocation associated with portal hypertension leads to systemic inflammation 2
• Impaired reticuloendothelial system function and abnormalities in both serum and ascitic fluid humoral immune systems contribute to infection risk 3

Malignant Ascites

• While less frequently reported, malignant ascites can also become infected with bacteria 1
• Patients with malignant ascites may develop features of both spontaneous and secondary peritonitis 1
• The SAAG (serum-ascites albumin gradient) is typically <11 g/L in peritoneal carcinomatosis, unlike cirrhotic ascites where SAAG is ≥11 g/L 2

Microbiology

• Gram-negative enteric bacteria are the most common pathogens (70% of cases), with Escherichia coli being predominant 3, 4
• Gram-positive cocci (mainly streptococcus species and enterococci) are also frequently isolated 2
• In patients with malignant ascites, polymicrobial infections have been reported 1

Clinical Presentation

• Fever and abdominal pain are the most common presenting symptoms 3
• Some patients may be asymptomatic or have subtle clinical manifestations 3
• In patients with malignant ascites, symptoms of infection may be mistaken for cancer-related symptoms 1
• Other presentations include:
  • Worsening ascites 2
  • Encephalopathy 4
  • Hypotension 4
  • Jaundice 4

Diagnostic Approach

• A diagnostic paracentesis should be performed in all patients with ascites who present with:

  • Fever or other signs of systemic inflammation 2
  • Abdominal pain 2
  • Worsening ascites 2
  • Worsening liver function 2
  • Encephalopathy 2
  • Hypotension 2

• Ascitic fluid analysis should include:

  • Cell count with differential 2
  • Culture (preferably in blood culture bottles) 2
  • Protein concentration 2

• Blood cultures should be obtained before starting antibiotic therapy 2

Risk Factors for SBP in Ascites

• Child-Pugh stage C (in cirrhotic patients) 5
• Elevated ascitic fluid PMN count (≥100 cells/μL) 5
• Low serum sodium levels 5
• Previous episodes of SBP 5

Management Considerations

• Prompt antibiotic therapy should be initiated as soon as SBP is diagnosed 6
• Empiric antibiotic therapy should cover the most common pathogens, particularly gram-negative bacteria 4
• Each hour of delay in diagnostic paracentesis after admission is associated with a 3.3% increase in in-hospital mortality 2
• In patients with malignant ascites who develop symptoms suggestive of infection, clinicians should maintain a high index of suspicion for bacterial peritonitis 1

Prognosis

• SBP is associated with significant mortality (approximately 20% in-hospital mortality with early diagnosis and prompt treatment) 2
• Poor prognostic factors include:
  • Elevated MELD score (≥22) 5
  • Elevated CRP levels (≥3.5 mg/dL) 5
  • Development of grade III/IV hepatic encephalopathy 5

Clinical Pitfalls to Avoid

• Failing to consider SBP in patients with malignant ascites who develop fever, abdominal pain, or worsening symptoms 1
• Attributing new symptoms solely to cancer progression without excluding infection 1
• Delaying diagnostic paracentesis, as each hour of delay increases mortality risk 2
• Relying only on culture results, as culture-negative neutrocytic ascites is common and should be treated similarly to culture-positive SBP 2