Abdominal Tuberculosis

Abdominal tuberculosis is infection of the peritoneum, gastrointestinal tract, abdominal lymph nodes or solid viscera by Mycobacterium tuberculosis, mostly through reactivation of latent foci, ingestion of sputum, or hematogenous spread.

It makes up 1 to 3% of all tuberculosis and 5 to 10% of extrapulmonary disease. Pulmonary disease is seen in only 15 to 25% of patients. Risk factors: HIV infection, cirrhosis, diabetes, chronic kidney disease (especially peritoneal dialysis), immunosuppressants including anti-TNF agents, malnutrition and alcohol use.

Forms

• Peritoneal: wet-type (ascites), dry plastic (adhesions, caseation) and fibrotic

• Intestinal: ileocecal in most cases, with ulcerative, hypertrophic or ulcerohypertrophic types

• Nodal: mesenteric, peripancreatic and portal nodes, with caseation

• Visceral: liver, spleen and pancreas

Complications: intestinal obstruction (strictures, adhesions), perforation (usually in the ulcerative form), fistula, malabsorption, hemorrhage and abdominal cocoon.

Treatment is highly effective, and mortality is about 5 to 10% mainly from delayed diagnosis and cirrhosis.

• Abdominal pain (80 to 90%), weight loss, fever, night sweats, anorexia and diarrhea or constipation, over weeks to months

• Ascites (doughy abdomen), a right iliac fossa mass, subacute obstruction, and lymphadenopathy

• Peritoneal: distension and diffuse tenderness

• Intestinal: obstructive symptoms, hematochezia and bowel sounds that are hyperactive

1. Ascitic fluid analysis: lymphocytic exudate (over 500 cells/microlitre with over 70% lymphocytes), serum-ascites albumin gradient under 11 g/L in most (but over 11 g/L in cirrhosis), protein over 30 g/L, and adenosine deaminase over 30 to 39 U/L (sensitivity about 90%).

2. Fluid and tissue microbiology: acid-fast smear (low yield, about 3%), Xpert MTB/RIF (sensitivity about 30% in fluid but higher in tissue), and culture (about 35 to 70%, with results at 2 to 6 weeks).

3. Laparoscopy with peritoneal biopsy: the best test (over 95%), showing miliary nodules, thickened peritoneum and adhesions, with caseating granulomas on histology.

4. Imaging: CT with contrast (ascites with high attenuation, thickened omentum, necrotic nodes with a hypodense center, ileocecal thickening) and ultrasound with fine septations.

5. Colonoscopy and ileoscopy with biopsy for ileocecal disease (transverse ulcers, nodules, a patulous ileocecal valve).

6. Supporting tests: chest radiograph, HIV test, interferon-gamma release assay, CA-125 (raised in peritoneal disease, which can mimic ovarian cancer).

Antituberculous therapy is the same as for pulmonary disease.

Standard regimen (6 months)

• Intensive phase (2 months): isoniazid 5 mg/kg (maximum 300 mg), rifampicin 10 mg/kg (maximum 600 mg), pyrazinamide 25 mg/kg (maximum 2 g) and ethambutol 15 to 20 mg/kg (maximum 1.2 g), all orally once daily.
• Continuation phase (4 months): isoniazid and rifampicin at the same doses once daily.
• Pyridoxine 10 to 25 mg orally daily with isoniazid.
• Longer therapy (9 to 12 months) for drug-resistant disease or slow response.
• Children: isoniazid 10 mg/kg (7 to 15), rifampicin 15 mg/kg (10 to 20), pyrazinamide 35 mg/kg (30 to 40) and ethambutol 20 mg/kg (15 to 25) once daily.

Monitoring: liver enzymes at baseline and every 2 weeks for 2 months, then monthly (stop all drugs if ALT is over 5 times the upper limit, or over 3 times with symptoms, then reintroduce sequentially), visual acuity and color vision with ethambutol, and uric acid and renal function.

HIV: start antiretroviral therapy within 2 weeks if CD4 count is under 50 cells/microlitre, otherwise within 8 weeks. Adjust for rifampicin interactions (dolutegravir 50 mg twice daily).

Pregnancy: use isoniazid, rifampicin and ethambutol with pyridoxine 25 mg daily, and pyrazinamide where local practice allows. Avoid streptomycin.

Adjuncts and surgery

• Steroids are not routinely given (no proven benefit in abdominal disease).
• Surgery for obstruction not responding to treatment, perforation, abscess, fistula or bleeding. Limit resections (strictureplasty, ileocecal resection) and avoid extensive bowel loss.
• Cefazolin 2 g IV with metronidazole 500 mg IV before surgery, and enteral or parenteral nutrition in malnourished patients.
• Drain large ascites only when symptomatic.

Follow-up monthly during therapy with weight, symptoms and ascites, and imaging at 3 to 6 months. Counsel on adherence, contact tracing and HIV screening.