Diagnosing Intestinal Tuberculosis
The diagnosis of intestinal tuberculosis requires a combination of clinical evaluation, imaging studies, endoscopy with biopsy, and microbiological testing, as no single test has sufficient sensitivity to establish the diagnosis definitively.
Clinical Presentation
Common symptoms:
- Fever (75%)
- Abdominal pain (65-82%)
- Weight loss (36-73%)
- Diarrhea (may be bloody)
- Night sweats 1
Physical findings:
- Abdominal tenderness
- Abdominal distension
- Palpable mass (in some cases)
Diagnostic Approach
Step 1: Initial Evaluation
Laboratory tests:
- Complete blood count (may show anemia)
- Elevated inflammatory markers (ESR, CRP)
- Liver function tests
- HIV testing (due to association with TB)
Tuberculin skin test (TST) or Interferon-Gamma Release Assay (IGRA):
- T-SPOT.TB has higher sensitivity (77%) compared to PPD (50%) 2
- Note: Negative results do not exclude intestinal TB
Chest X-ray:
- Important to evaluate for pulmonary TB
- Up to 85% of abdominal TB patients may not have pulmonary involvement 1
Step 2: Imaging Studies
CT scan of abdomen:
- Look for:
- Thickened bowel wall (especially ileocecal region)
- Lymphadenopathy with central hypodensity and peripheral enhancement
- Ascites (if peritoneal involvement)
- Lipohydric level with necrotic lymph nodes (highly specific for tuberculous ascites) 1
- Look for:
Ultrasonography:
- May show ascites, lymphadenopathy, bowel wall thickening
- Less sensitive than CT scan
Step 3: Endoscopy with Biopsy
Colonoscopy with ileoscopy:
Histopathology:
- Look for:
- Caseating granulomas
- Acid-fast bacilli (AFB) staining
- Sensitivity of histopathology: approximately 68% 3
- Look for:
Step 4: Microbiological Testing
Culture:
- Gold standard but low sensitivity (9.3%) 3
- MGIT BACTEC system is recommended medium
- May take 2-6 weeks for results
Molecular testing:
Step 5: Additional Procedures (if diagnosis remains unclear)
Laparoscopy with peritoneal biopsy:
- Useful for peritoneal TB
- Allows direct visualization and targeted biopsy
Ascitic fluid analysis (if present):
- Exudative with lymphocyte predominance
- Adenosine deaminase (ADA) levels >33 U/L (high sensitivity and specificity)
Differential Diagnosis
Crohn's disease (most important differential):
- Features favoring Crohn's: aphthous ulcers, longitudinal ulcers, cobblestone appearance, anorectal lesions
- Features favoring TB: patulous ileocecal valve, transverse ulcers, scars/pseudopolyps 1
Other conditions to consider:
- Malignancy
- Infectious colitis
- Ischemic colitis
Diagnostic Challenges
- Low yield of conventional tests (AFB staining, culture)
- Overlap of clinical, endoscopic, and histological features with Crohn's disease
- Lack of pulmonary TB in majority of cases
- Variable presentation depending on site of involvement
Treatment
Once diagnosed, intestinal TB is primarily treated medically with standard anti-TB regimen:
- Initial phase: Isoniazid, Rifampin, Pyrazinamide, and Ethambutol for 2 months
- Continuation phase: Isoniazid and Rifampin for 4 months
- Total treatment duration: 6 months 1, 4, 5
Surgery is reserved for complications such as perforation, where resection and anastomosis is preferred over direct suture repair 1.
Common Pitfalls to Avoid
- Misdiagnosing as Crohn's disease - critical to differentiate as treatment approaches differ significantly
- Relying on a single test - no single test has adequate sensitivity
- Overlooking TB in non-endemic areas - consider TB even in low-prevalence settings
- Waiting for culture results - empiric treatment may be necessary if clinical suspicion is high
- Missing extrapulmonary TB - always evaluate for TB at other sites