What is the diagnosis and treatment approach for abdominal tuberculosis (TB)?

Diagnosis of Abdominal Tuberculosis

Abdominal tuberculosis requires a high index of suspicion in patients presenting with fever, abdominal pain, and weight loss, particularly those from endemic areas, with diagnosis confirmed through tissue sampling (endoscopic or laparoscopic biopsy) for histopathology and culture, followed by standard 6-month four-drug anti-TB therapy. 1, 2

Clinical Presentation and When to Suspect

Suspect abdominal TB in patients presenting with:

• Fever (70-84% of cases), abdominal pain (65-88%), and weight loss (36-68%) 2
• Ascites (30-67% of cases), which may be free or loculated 2
• Night sweats accompanying fever 2

Critical caveat: Up to 85% of patients with abdominal TB have no pulmonary involvement, so absence of lung disease does not exclude the diagnosis 1, 2. This makes diagnosis particularly challenging and requires heightened clinical suspicion 3.

High-Risk Populations Requiring Lower Threshold for Suspicion:

• Immigrants from endemic areas (Asia, Africa) 2
• HIV/AIDS patients 2
• Immunosuppressed individuals 2
• Patients with positive tuberculin skin test 2

Anatomical Distribution

The ileocecal region and terminal ileum are involved in 50-90% of gastrointestinal TB cases, making this the most critical area to evaluate 1, 2, 4. Intestinal TB represents 58-60% of all abdominal TB cases 2.

Diagnostic Algorithm by Clinical Category

The diagnostic approach should be categorized based on presentation pattern 3:

1. Gastrointestinal Involvement (Ileocecal/Intestinal)

• First-line approach: Endoscopy with biopsy 3
• MDCT enterography shows characteristic findings: short-segment strictures with symmetrical concentric mural thickening and homogeneous mural enhancement 4
• Barium studies may be normal in early disease 5
• Common pitfall: The presentation can closely mimic Crohn's disease, particularly in the ileocecal region, but night sweats and positive tuberculin skin test favor TB 2

2. Wet Peritonitis (Ascites)

• Ultrasound-guided aspiration of ascitic fluid for analysis 3
• If aspiration non-diagnostic, proceed to laparoscopy with peritoneal biopsy 3
• Ascitic fluid analysis can confirm diagnosis in some cases 5

3. Lymphadenopathy

• Sonographically-guided biopsy of mesenteric lymph nodes 5, 3
• If ultrasound-guided biopsy fails, proceed to laparoscopy 3

4. Solid Organ Lesions

• Ultrasound-guided aspiration 3

5. Dry/Fixed Peritonitis

• Endoscopy as first approach 3
• Diagnostic laparotomy should be kept as the last option for achieving histological diagnosis 3

Imaging Findings

Ultrasound (Particularly Useful in Resource-Limited Settings)

Characteristic sonographic features of early abdominal TB include:

• Mesenteric thickness ≥15 mm with increased echogenicity (due to fat deposition) 5
• Mesenteric lymphadenopathy 5
• Dilated small bowel loops (68% of cases) 5
• Minimal ascites (30% of cases) 5
• Omental thickening with altered echogenicity 5

MDCT Enterography

• Allows comprehensive assessment of well-distended bowel loops 4
• Shows thickness and enhancement of entire bowel wall in all three planes 4
• Most common finding: Short-segment strictures with symmetrical concentric mural thickening and homogeneous mural enhancement 4
• Additional findings: lymphadenopathy, ascites, enteroliths, peritoneal thickening 4

Microbiological and Molecular Diagnosis

Critical limitation: Due to the paucibacillary nature of abdominal TB, sensitivity of AFB smear, culture, and PCR assays are usually lower than in pulmonary TB 6, 7. This necessitates tissue diagnosis.

Recommended Diagnostic Tests:

• AFB smear and mycobacterial culture from tissue samples (gold standard when positive) 7
• Histopathological examination of biopsy specimens 7
• Nucleic acid amplification tests (NAATs): PCR/multiplex-PCR and nested PCR show reasonable sensitivity/specificity 6
• GeneXpert MTB/RIF: Reveals low sensitivity but high specificity, useful for differential diagnosis of intestinal TB versus Crohn's disease 6
• Real-time PCR for circulating M. tuberculosis cell-free DNA in ascitic fluid 6

A definite diagnosis can be reached in only 80% of patients; therapeutic diagnosis (empiric treatment with clinical response assessment) should be tried in the remaining 20% 3.

Treatment

Standard Medical Therapy

The recommended regimen is 6 months: isoniazid, rifampin, pyrazinamide, and ethambutol for the initial 2 months (intensive phase), followed by isoniazid and rifampin for 4 months (continuation phase) 1, 2.

• Initial intensive phase: Daily administration of all four drugs 1
• Continuation phase: Daily isoniazid and rifampin 1

Extended Treatment Indications:

• HIV-positive patients: Extend treatment to at least 9 months 1
• Patients who remain culture-positive 2
• Resistant organisms 2
• Fluoroquinolone-susceptible multidrug-resistant TB with extrapulmonary involvement: 9-month all-oral regimen 1

Surgical Management

Surgery is reserved for specific complications 1:

• Intestinal perforation (resection and anastomosis is preferred procedure) 1, 2
• Intestinal obstruction not responding to medical therapy 2
• Diagnostic uncertainty requiring tissue diagnosis 2
• Fistula formation 2

Common pitfall: Delaying surgical intervention when complications like perforation or obstruction occur can lead to increased morbidity 2, 7.

Follow-Up Monitoring

• Close follow-up is needed to evaluate effectiveness of treatment 7
• Ultrasound can document regression of mesenteric thickening, lymphadenopathy, and ascites at 1,3,6, and 12 months after starting therapy 5
• Endoscopic interventions may be required for managing complications during treatment 7