Microscopic detection of bacillus Calmette–Guérin mycobacteria in bladder biopsy using fluorescence in situ hybridization: Détection microscopique des Bacilles biliés de Calmette et Guérin (BCG) dans une biopsie vésicale par hybridation in situ en fluorescence

Intravesical instillation of Bacilli Calmette Guérin (BCG) as a superficial bladder cancer treatment is generally well tolerated, but local or systemic complications may occur, some of which may be life-threatening. Following the suspicion of post-BCG cystitis in a 72-year-old man with a history of urothelial carcinoma treated by intravesical BCG instillation, we used fluorescence in situ hybridization (FISH) targeting the rpoB gene of the Mycobacterium tuberculosis complex to detect Mycobacterium bovis BCG in paraffin-embedded bladder biopsy sections. FISH yielded specific detection of BCG mycobacteria in the bladder biopsy section, appearing as red-fluorescent bacilli. Treatment with rifampicin, ethambutol and isoniazid is then initiated in combination with corticosteroid therapy.