Histopathology of Disseminated Mycobacterium bovis Infection Complicating Intravesical BCG Immunotherapy for Urothelial Carcinoma

Intravesical instillation of Bacillus Calmette-Guerin (BCG) is a mainstay of adjunctive therapy for superficial bladder cancer. Disseminated BCG infection (BCG-osis) after this therapy is rare and potentially life-threatening; only isolated case reports detail the histopathologic findings thereof, few of which had a diagnosis confirmed by molecular testing. We report 3 additional cases of BCG-osis complicating BCG therapy, all confirmed by cultures and molecular assays, including the first cases of wedge biopsy-confirmed BCG pneumonia and BCG olecranon bursitis. When suggested by a relevant clinical history, recognition of randomly distributed granulomas in any organ should prompt consideration of BCG-osis and liberal performance of AFB stains, aided by targeted molecular assays. Physicians should maintain a high index of suspicion when miliary infiltrates arise after intravesical BCG instillation, and close multidisciplinary communication is essential. Pathologist awareness of this rare cause of granulomatous inflammation aids recognition of BCG-osis and facilitates prompt initiation of antimycobacterial therapy.