What is the diagnostic workup for intestinal tuberculosis (TB)?

Diagnostic Workup for Intestinal Tuberculosis

The diagnosis of intestinal tuberculosis requires a comprehensive approach combining clinical assessment, imaging studies, endoscopy with biopsies, and microbiological/molecular testing to ensure accurate diagnosis and appropriate treatment. 1

Clinical Assessment

Risk Factors to Identify

• History of residence in TB-endemic areas
• Immunosuppression (especially HIV)
• Contact with active TB patients
• History of pulmonary TB (present in less than half of intestinal TB cases) 2

Common Symptoms

• Abdominal pain
• Weight loss
• Fever (often low-grade)
• Night sweats
• Change in bowel habits
• Anorexia
• Nausea and vomiting 2

Diagnostic Imaging

Abdominal CT Scan

• Look for:
  • Intestinal wall thickening
  • Mesenteric lymphadenopathy
  • Ascites
  • Lipohidric levels associated with necrotic lymph nodes (highly specific finding) 1

Endoscopy and Biopsy

Colonoscopy

• Essential diagnostic procedure
• Characteristic findings:
  • Stenosis
  • Nodules
  • Fistulas
  • Ulcerations 1

Biopsy Technique

• Multiple and deep biopsies from ulcer bases are recommended
• Increases diagnostic yield significantly
• Samples should be sent for:
  • Histopathology (look for granulomas)
  • AFB staining
  • Culture for M. tuberculosis
  • PCR testing 1

Laboratory Tests

Microbiological Testing

• GeneXpert MTB/RIF test:
  • Sensitivity: 81-95.7%
  • Specificity: 91-100% 1

PCR for M. tuberculosis

• Sensitivity: 21.6-65%
• Specificity: 93-100% 1

Additional Tests

• Tuberculin skin test (TST)
  • Apply 0.1 mL of PPD (5 TU) intracutaneously
  • Read between 48-72 hours by trained personnel
  • Self-reading should not be accepted 3
• Interferon-gamma release assays (IGRAs)
  • Preferred in BCG-vaccinated individuals 3

Differential Diagnosis

Crohn's Disease

• Primary differential diagnosis
• Distinguishing features:
  • Longitudinal lesions
  • Aphthous ulcers
  • Cobblestone appearance in Crohn's disease 1

Other Considerations

• Malignancy
• Other infectious colitis
• Mycobacterium avium complex (MAC) infection 4

Diagnostic Algorithm

1. Initial Evaluation:

   • Clinical assessment for TB risk factors
   • Chest X-ray to rule out pulmonary TB

2. Laboratory Testing:

   • Complete blood count (leukopenia may be present but is nonspecific) 5
   • TST and/or IGRA

3. Imaging:

   • Abdominal CT scan

4. Endoscopic Evaluation:

   • Colonoscopy with multiple biopsies

5. Specimen Processing:

   • Histopathology
   • AFB staining
   • Culture for M. tuberculosis
   • PCR/GeneXpert testing

6. If Diagnosis Remains Uncertain:

   • Consider therapeutic trial with anti-TB therapy when clinical suspicion is high
   • Evaluate response to treatment 1

Common Pitfalls and Caveats

• Intestinal TB often mimics Crohn's disease, leading to diagnostic confusion 6
• Pulmonary TB is absent in more than half of intestinal TB cases 2
• False-negative TST results may occur in patients on immunosuppressive therapy 3
• Leukopenia is common but nonspecific 5
• Diagnosis must be confirmed by histologic examination; if inconclusive, acid-fast bacilli must be seen or culture should be positive 5

Special Considerations

• In immunocompromised patients, maintain a high index of suspicion
• In patients with suspected Crohn's disease, always rule out intestinal TB before starting immunosuppressive therapy 1
• Consider both conditions may coexist in rare cases 6