Mycobacterium bovis Osteomyelitis Following Intravesical Bacille Calmette-Guérin Immunotherapy

Intravesical Bacille Calmette-Guérin (BCG) immunotherapy is a standard treatment for high-risk or intermediate-risk nonmuscle-invasive bladder cancer (NMIBC). BCG is a live-attenuated strain of Mycobacterium bovis , a member of the Mycobacterium tuberculosis complex (MTBC). Although systemic complications are rare, disseminated BCG infection (“BCG-osis”)—including BCG osteomyelitis—remains a possibility. However, identifying BCG as the causative organism in these cases may be delayed by the insidious nature of mycobacteria and their potential to mimic malignant processes. We present 2 cases of BCG osteomyelitis following BCG immunotherapy, discuss their diagnostic challenges, and highlight the importance of prior BCG exposure in guiding appropriate antimicrobial therapy.