Diagnosis of Abdominal Tuberculosis

1. Clinical Suspicion (First Step)

• Persistent fever, night sweats, weight loss, anorexia
• Abdominal pain - especially ileocecal region
• Ascites (especially exudative with high protein)
• Risk factors: HIV infection, immunosuppression, cirrhosis, endemic country origin, contact with bovine TB

2. Forms and Their Diagnostic Features

A. Intestinal (Gastrointestinal) TB

• Presents with abdominal pain, obstruction, hematochezia, palpable mass
• Ulcerations and fistulae can mimic Crohn's disease - differentiation is a major clinical challenge
• Anal fistulae warrant rectal TB evaluation

B. Tuberculous Peritonitis

• Arises from direct spread of tubercle bacilli from ruptured lymph nodes, intraabdominal organs (e.g., genital TB in women), or hematogenous seeding
• Key triad: nonspecific abdominal pain + fever + ascites
• Coexistence of cirrhosis complicates diagnosis (both cause ascites)

3. Diagnostic Investigations

Ascitic Fluid Analysis (for peritoneal TB)

Lab Tests

• AFB smear and culture of ascitic fluid, stool, biopsy specimens - gold standard but paucibacillary nature limits sensitivity
• Tuberculin skin test / IGRA - helpful supportive evidence
• Serum markers - non-specific (elevated ESR, CRP, hypoalbuminemia)

Nucleic Acid Amplification Tests (NAATs / PCR)

• Pooled sensitivity ~58% (vs clinical reference standard) and specificity ~99% for abdominal TB - Shen et al., PLoS ONE 2023, PMID 38011098
• Multiplex PCR (multiple target genes) improves sensitivity
• Stool specimens are a viable non-invasive option alongside tissue and ascitic fluid
• Xpert MTB/RIF (GeneXpert) is highly specific; useful on biopsy tissue

Imaging

Endoscopy with Biopsy (Colonoscopy)

• Colonoscopy reaching the ileocecal region is the most important diagnostic tool for intestinal TB
• Shows ulcers (circumferential, transverse), nodules, strictures, deformed ileocecal valve
• Biopsy for histology (caseating granulomas) + culture is key
• Combined granuloma identification + biopsy culture improves diagnostic yield

Laparoscopy (Gold Standard for Peritoneal TB)

• Direct visualization of peritoneum - shows characteristic white miliary nodules or yellow-white deposits
• Peritoneal biopsy: reveals granulomas and/or positive culture in up to 80% of cases
• Recommended when diagnosis is strongly suspected but cannot be confirmed by other means - Harrison's 22e; Sleisenger & Fordtran's
• Also used in intestinal TB when surgery is ultimately required

Histology

• Caseating granulomas are the hallmark finding
• Langerhans giant cells, epithelioid cells
• AFB staining of tissue (Ziehl-Neelsen) - confirms diagnosis when positive

4. Diagnostic Algorithm Summary

Clinical suspicion (fever + abdominal symptoms + risk factors)
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Blood tests + Chest X-ray (look for pulmonary TB)
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Ultrasound / CT abdomen
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If ascites → Paracentesis: exudate, lymphocytosis, ADA, AFB culture, PCR
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Colonoscopy + biopsy (ileocecal TB)
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If still inconclusive → Laparoscopy with peritoneal biopsy (GOLD STANDARD)
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Histology: caseating granulomas + culture/PCR confirmation

5. Differentiating TB from Crohn's Disease

Key Points to Remember

• Diagnosis is delayed because symptoms are vague and the organism is paucibacillary
• Laparoscopy + peritoneal biopsy is the definitive method when other tests fail
• PCR/NAATs have high specificity (99%) but moderate sensitivity (~58%) on ascitic fluid/tissue
• ADA in ascitic fluid is useful but unreliable in cirrhotics
• Therapeutic trial with anti-TB drugs (2RHZE/4RHE) may be justified when definitive diagnosis cannot be obtained and clinical suspicion is high
• Surgery is needed for complications: obstruction, perforation, fistula