GRANULOMATOUS PERITONITIS CAUSED BY MYCOBACTERIUM BOVIS AFTER INTRAVESICAL BCG INSTILLATION: AN UNCOMMON AND POTENTIALLY SEVERE COMPLICATION

The BCG vaccine (bacillus Calmette-Guérin), made from live attenuated strains of Mycobacterium bovis , is used as adjuvant therapy to prevent recurrence of non-invasive bladder carcinomas, with good response rates. Dissemination of the bacillus is an extremely rare complication, estimated at 0.4%, but potentially severe, and may manifest as pneumonitis, skin infection, meningitis, hepatitis, and sepsis. Peritonitis is the rarest complication reported in the literature. A 45-year-old woman diagnosed with high-grade papillary urothelial carcinoma of the bladder underwent surgical treatment with transurethral resection of the lesion, followed by immunotherapy with intravesical BCG instillation. One month after initiation of therapy, after three administrations, she developed abdominal pain, nausea, vomiting, and fever (38.3°C). Upon admission, abdominal computed tomography revealed diffuse thickening of peritoneal planes and mesenteric layers, suggestive of peritonitis. Abdominal fluid aspiration showed 6,636 cells/mm³ (50% macrophages) and adenosine deaminase (ADA) of 59 U/L. Diagnostic videolaparoscopy demonstrated micronodular lesions in the pelvic peritoneum and throughout the omentum. Histopathological examination confirmed granulomatous lesions, with a positive rapid molecular test for the M. tuberculosis complex. Culture of the tissue fragment grew acid-fast bacilli, later identified as M. bovis . The patient was treated with rifampicin combined with isoniazid and ethambutol, with good clinical response, and is currently under outpatient follow-up. We present a case of granulomatous peritonitis caused by M. bovis following intravesical BCG instillation, confirmed by histopathology and culture. The most common complications of this procedure are local symptoms such as dysuria and abdominal pain, as well as systemic signs and symptoms such as fever, respiratory distress, and hypotension, related to intense cytokine release into the bloodstream. When bacillary dissemination occurs rather than hypersensitivity reaction alone, the most affected organs are the liver and lungs, with peritoneal involvement rarely described. Although rare, extravesical M. bovis infection after BCG instillation can be fatal and should be considered in all patients presenting systemic symptoms after therapy.