What are the potential causes of a 2-month duration fever with abdominal pain in a patient, considering demographics, past medical history, and potential exposures to infectious diseases like tuberculosis?

Prolonged Fever with Abdominal Pain: Differential Diagnosis

In a patient with 2 months of fever and abdominal pain, tuberculosis peritonitis must be the primary diagnostic consideration, particularly in immigrants from endemic regions, followed by intra-abdominal abscess, inflammatory bowel disease complications, and lymphoma. 1, 2, 3

Key Diagnostic Considerations

Tuberculosis Peritonitis

• Abdominal TB presents classically with fever (70%), abdominal pain (70%), weight loss (68%), and abdominal distension/ascites (67%) over weeks to months 3
• The ileocecal region and peritoneum are the most commonly affected sites, typically from hematogenous spread or swallowing infected sputum 2
• Active pulmonary TB is present in less than half of patients with abdominal TB, making chest imaging alone insufficient to exclude the diagnosis 2
• TB skin testing is positive in only 27% of patients with abdominal TB, so a negative test does not rule out disease 3
• Patients from Haiti, other endemic regions, homeless populations, prisoners, long-term care residents, and immunocompromised individuals are at highest risk 2

Intra-abdominal Abscess

• Abscesses present with fever, diffuse or localized abdominal pain, and may have predisposing conditions including appendicitis, diverticulitis, inflammatory bowel disease, or pancreatitis 4
• Malignant conditions including lymphoma and necrotizing masses can present identically with abdominal pain and fever 4
• In elderly patients, laboratory tests may be nonspecific and normal despite serious infection 4

Inflammatory Bowel Disease Complications

• Crohn's disease with associated abscess or phlegmon presents with fever and abdominal pain 4
• Complications may develop insidiously over weeks to months

Immediate Diagnostic Workup

Imaging

CT abdomen and pelvis with IV contrast is the preferred initial imaging study for this presentation, as it:

• Changes the leading diagnosis in 49% of cases, alters admission status in 24%, and modifies surgical plans in 25% 4
• Detects abscesses, peritoneal thickening, lymphadenopathy, omental masses, and bowel abnormalities 4
• In abdominal TB, CT shows ascites (80%), peritoneal lesions, enlarged lymph nodes, omental thickening, and dilated bowel loops 1, 3
• Increases detection of cholecystitis/cholangitis by 100% and pelvic inflammatory disease by 280% compared to clinical assessment alone 4

Invasive Diagnostic Procedures

When CT suggests TB or lymphoma:

• Paracentesis with ascitic fluid analysis for cell count, protein, glucose, cytology, acid-fast bacilli smear and culture (diagnostic in 33% of TB cases) 3
• Peritoneal biopsy via laparoscopy or laparotomy shows granulomas in 97% and positive smear/culture in 68% of TB cases 3
• Ultrasound-guided omental or peritoneal mass biopsy for histopathology and culture 1, 5

Laboratory Studies

• Sputum and gastric aspirate cultures for Mycobacterium tuberculosis, even without respiratory symptoms 1, 6
• HIV testing, as immunocompromised patients have atypical presentations 1
• Complete blood count, though may be nonspecific 4
• Urine TB PCR/nucleic acid amplification testing for genitourinary TB 5

Chest Imaging

• Chest X-ray or CT to identify active or inactive pulmonary TB, present in 30% of abdominal TB cases 3, 6
• Miliary pattern on chest CT is pathognomonic for disseminated TB 5

Critical Pitfalls to Avoid

• Do not delay diagnosis by relying on TB skin testing alone—it is positive in only 27% of abdominal TB cases 3
• Do not assume absence of pulmonary symptoms excludes TB—over half of abdominal TB patients have no active lung disease 2
• Plain abdominal radiographs have low sensitivity (limited role) and should not delay CT imaging 4
• Neutropenic or immunocompromised patients may lack typical signs of infection, leading to delayed diagnosis and high mortality 4
• Atypical presentations exist: miliary TB can present without granulomas on initial biopsy but with abundant acid-fast bacilli 5

Treatment Approach

For Confirmed or Highly Suspected TB

• Initiate standard 4-drug anti-TB therapy (isoniazid, rifampin, pyrazinamide, ethambutol) for 9-12 months 3
• Patients typically respond dramatically within days to weeks of starting therapy 1, 5
• Surgery is rarely required unless complications develop 2

For Abscess

• Percutaneous drainage under CT or ultrasound guidance combined with broad-spectrum antibiotics 4
• Surgery reserved for complications including perforation or failed percutaneous drainage 4

For Neutropenic Enterocolitis

• Broad-spectrum antibiotics with bowel rest; surgery only for perforation or ischemia 4