What is the recommended approach to diagnose tuberculosis from the terminal ileum?

Diagnosing Tuberculosis from the Terminal Ileum

Colonoscopy with multiple biopsies from the terminal ileum is the recommended approach for diagnosing tuberculosis from the terminal ileum, combined with appropriate microbiological testing including rapid molecular tests, culture, and drug susceptibility testing. 1

Diagnostic Algorithm

1. Endoscopic Evaluation

• Ileocolonoscopy with biopsies: This is the cornerstone of diagnosis for terminal ileal tuberculosis 1
  • Obtain multiple biopsies from the terminal ileum, including from both normal and abnormal-appearing areas
  • Look for characteristic endoscopic features:
    • Patulous ileocecal valve
    • Transverse ulcers
    • Scars or pseudopolyps
    • Localized involvement 1

2. Microbiological Testing of Biopsy Specimens

• Rapid molecular testing: WHO-recommended tests should be performed on all biopsy samples 1
• Mycobacterial culture: Essential for species identification and drug susceptibility testing 1
• Acid-fast bacilli (AFB) smear: Though less sensitive, should be performed on all specimens 1
• Histopathological examination: Look for caseating granulomas, which are suggestive of tuberculosis 1

3. Imaging Studies

• CT enterography or MR enterography: These are preferred imaging modalities 1
  • Look for:
    • Preferential thickening of the ileocecal valve and medial wall of the cecum
    • Regional lymphadenopathy
    • Inflammatory mass extending into adjacent muscle 2
    • Strictures in the terminal ileum 1

4. Additional Diagnostic Tests

• Interferon-gamma release assay (IGRA) or tuberculin skin test (TST): To detect TB infection 1
• Stool studies: To exclude other infectious causes 3
• Fecal calprotectin: To assess inflammatory activity 1

Differentiating from Crohn's Disease

Terminal ileal tuberculosis often mimics Crohn's disease, making differential diagnosis challenging 4. Key distinguishing features include:

Feature	Tuberculosis	Crohn's Disease
Endoscopic appearance	Transverse ulcers, patulous ileocecal valve	Longitudinal/aphthous ulcers, cobblestone appearance
Involvement pattern	Localized (primarily ileocecal)	Skip lesions throughout GI tract
Wall thickening	Variable, often asymmetric	Uniform, less pronounced
Lymphadenopathy	Common, often necrotic	Less common
Histopathology	Caseating granulomas	Non-caseating granulomas

Pitfalls and Caveats

1. Sampling error: Multiple biopsies from different sites are essential as tuberculosis can have patchy involvement 1

2. False negatives: Acid-fast bacilli may be difficult to detect in paucibacillary intestinal TB; negative smear does not rule out TB 5

3. Misdiagnosis as Crohn's disease: This is common and can lead to inappropriate immunosuppressive therapy, which may worsen tuberculosis 4

4. Surgical specimens: When surgery is performed for other reasons (e.g., suspected appendicitis), any terminal ileal specimens should be saved in normal saline for microbiological testing and in formalin for histopathology 1

5. Extrapulmonary TB: Remember that patients may not have concurrent pulmonary TB, so negative chest imaging does not exclude intestinal TB 1

By following this systematic approach to diagnosis, tuberculosis of the terminal ileum can be identified accurately, allowing for appropriate treatment to be initiated promptly, which is crucial for reducing morbidity and mortality associated with this condition.