What are the key differences in diagnosis and treatment between dengue fever and abdominal tuberculosis (TB) in a patient presenting with similar symptoms?

Key Differences Between Dengue Fever and Abdominal Tuberculosis

Diagnostic Approach

The fundamental distinction lies in the diagnostic timeline and methods: dengue requires PCR/NAAT within the first week of symptoms or IgM testing after 5-7 days, while abdominal TB demands tissue diagnosis through endoscopy, laparoscopy, or biopsy showing caseating granulomas. 1, 2, 3

Clinical Presentation Differences

Dengue fever presents with:

• Acute onset with incubation period of 3-14 days (typically 4-8 days) after mosquito exposure 1, 2
• Frontal headache, retro-orbital pain, muscle and joint pain, and characteristic rash 1
• Fever typically resolves within 5 days of treatment 2
• Thrombocytopenia and rising hematocrit are hallmark findings 2
• No abdominal mass or lymphadenopathy 1, 2

Abdominal tuberculosis presents with:

• Chronic, insidious onset with fever (75%), abdominal pain (65%), and weight loss (36%) over weeks to months 3, 4
• Night sweats are characteristic 3
• Abdominal mass (26-42%), ascites (37-61%), and cachexia (75%) are common 4, 5
• Mesenteric lymphadenopathy with peripheral enhancement and central hypodensity on imaging 3
• Doughy abdomen on examination (9%) 5

Laboratory and Imaging Distinctions

For dengue:

• PCR/NAAT on serum is diagnostic within first 7 days of symptoms 1, 2
• NS1 antigen detection from day 1 up to 10 days after symptom onset 1
• IgM antibodies develop during first week and remain detectable for 2-3 months 1
• Complete blood count shows thrombocytopenia (often <100,000/mm³) and hemoconcentration 2
• Chest radiograph and abdominal imaging are typically normal 1, 2

For abdominal TB:

• CT scan abnormalities in 80-100% of cases showing ascites, peritoneal lesions, or enlarged nodes 5, 6
• Ascitic fluid density of 20-45 Hounsfield units with lipohydric level highly specific 3
• Terminal ileum and ileocecal region involvement in 50% of cases 3
• Histopathology showing caseating granulomas is diagnostic (positive in 97% when biopsy obtained) 5
• Acid-fast bacilli on smear in only 34%, culture positive in 60% 6
• Tuberculin skin test positive in only 27% of patients 5
• 85% have no pulmonary involvement on chest radiograph 3

Critical Diagnostic Pitfalls

Common errors in dengue diagnosis:

• Ordering IgM testing before day 5-7 when antibodies have not yet developed 1
• Missing cross-reactivity with other flaviviruses (Zika, West Nile, yellow fever) on serological testing 1
• Failing to test pregnant women comprehensively with both NAAT and serology 1, 2

Common errors in abdominal TB diagnosis:

• Relying on tuberculin skin test (negative in 73% of cases) 5
• Assuming normal chest radiograph excludes TB (85% have no pulmonary disease) 3, 6
• Failing to obtain tissue diagnosis—neither clinical features, laboratory, radiological, nor endoscopic methods alone provide gold standard diagnosis 4
• Confusing with Crohn's disease: TB shows transverse ulcers, patulous ileocecal valve, and fewer than 4 colonic segments involved, while Crohn's shows longitudinal ulcers, anorectal lesions, and cobblestoning 3

Treatment Differences

Dengue management:

• Supportive care only—acetaminophen for fever, aggressive oral hydration (>2500ml daily) 2, 7
• Never use aspirin or NSAIDs due to bleeding risk 2, 7
• Fluid resuscitation with 20 mL/kg bolus for dengue shock syndrome 2, 7
• No antibiotics indicated unless secondary bacterial infection documented 2
• Discharge when afebrile ≥48 hours without antipyretics 2, 7

Abdominal TB management:

• Medical therapy is primary treatment: standard 6-month anti-tubercular regimen 3
• Surgery only for complications (perforation, obstruction)—resection with anastomosis preferred over primary closure 3
• Therapeutic diagnosis trial appropriate in 20% where definitive diagnosis cannot be reached 8
• Treatment duration: 9-12 months with close supervision 4
• Response assessment at 9 months with symptom resolution expected 4

Algorithmic Approach to Differentiation

When patient presents with fever and abdominal symptoms:

1. Timeline assessment:

   • Acute onset (days): Consider dengue 1, 2
   • Chronic onset (weeks-months): Consider abdominal TB 3, 4

2. Travel and exposure history:

   • Recent travel to dengue-endemic area with mosquito exposure: Order dengue PCR if <7 days, IgM if >7 days 1, 2
   • Born in or lived in TB-endemic area: Pursue TB workup 3

3. Physical examination findings:

   • Rash, retro-orbital pain, no organomegaly: Dengue likely 1, 2
   • Abdominal mass, ascites, doughy abdomen, night sweats: TB likely 3, 4, 5

4. Initial laboratory:

   • Thrombocytopenia with hemoconcentration: Dengue 2
   • Normal platelets with chronic anemia: TB more likely 4

5. Imaging:

   • Normal CT abdomen: TB essentially excluded 5, 6
   • Mesenteric lymphadenopathy, ascites, bowel wall thickening: Pursue TB diagnosis with endoscopy/biopsy 3, 8

For abdominal TB diagnostic workup, categorize by presentation 8:

• Gastrointestinal symptoms: Endoscopy with biopsy
• Solid organ lesions: Ultrasound-guided aspiration
• Wet peritonitis/lymphadenopathy: Ultrasound-guided aspiration, then laparoscopy if needed
• Dry peritonitis: Endoscopy
• Diagnostic laparotomy reserved as last option 8

Special Population Considerations

Pregnant women:

• Both conditions require comprehensive testing due to risk of maternal death and adverse outcomes 1, 2
• Dengue: Test with both NAAT and serology regardless of outbreak patterns 1, 2
• TB: Consider in differential for ileocecal disease, especially if from endemic area 3
• Acetaminophen is safest analgesic for both conditions 2, 7