When the Cows Come Home: The Diagnostic Challenge of Mycobacterial Peritonitis

Abstract

A 56-year-old West African man presented with a 50-pound weight loss over three months and three days of right lower quadrant abdominal pain. His physical exam was notable for abdominal distention, mild abdominal tenderness, lungs that were clear to auscultation, and a lack of stigmata of chronic liver disease. Computerized tomography (CT) demonstrated moderate ascites, diffuse peritoneal enhancement and nodularity, and no pulmonary disease. Paracentesis showed exudative fluid with a serum albumin-to-ascites gradient of 0.6 and lymphocyte predominance, prompting concern for tubercular peritonitis. Beyond nationality, no further risk factor for Mycobacterium tuberculosis could be identified. Further questioning revealed that he had consumed unpasteurized goat milk at a farm in Guinea, raising suspicion for Mycobacterium bovis. A laparoscopic peritoneal biopsy showed mesothelial lined fibrous and adipose tissue with focally caseating granulomas. Although culture with Ziehl-Neelsen stain of the ascites fluid was negative, he was treated with two months of rifampin, isoniazid, pyrazinamide, and ethambutol, followed by an empiric isoniazid and rifampin course for M. bovis that was lengthened given presumed pyrazinamide resistance. After four months of therapy, the patient reports significant improvement in his symptoms. Only 2% of extrapulmonary disease affects the peritoneum, and only 3.1% of patients with mycobacterial disease are infected with M. bovis. M. bovis is transmitted to humans mainly through the consumption of unpasteurized milk. In industrialized nations M. bovis is almost nonexistent due to strict regulations. Symptoms are non-specific; vague abdominal pain and distention are common complaints. Peritoneal culture with Ziehl-Neelsen is positive in only 3% of confirmed cases of mycobacterial peritonitis. Therefore, laparoscopy is preferred; histopathology findings of granulomas with caseating necrosis are diagnostic of mycobacterial peritonitis. Routine diagnostic modalities often cannot differentiate between M. bovis and M. tuberculosis when cultures are negative. Despite the many similarities among M. bovis and M. tuberculosis, it is important to note that treatment is longer and prognosis is worse for M. bovis. This case reminds us of the diagnostic challenge of mycobacterial peritonitis and the importance of considering M. bovis, especially in patients presenting from endemic areas.