Chronic Granulomatous Interstitial Nephritis Presenting Five Years After Intravesical Bacillus Calmette-Guérin Therapy: A Case Report and Literature Review.

Intravesical administration of Bacillus Calmette-Guérin (BCG) has been the standard treatment for non-muscle invasive bladder cancer (NMIBC).  Its efficacy in preventing recurrence and tumor progression has been well established; however, rare immune-mediated complications, particularly parenchymal renal involvement, pose significant diagnostic challenges. This report describes an exceptional case: that of a 73-year-old man who developed renal failure five years after his last BCG instillation. Histopathological examination revealed granulomatous interstitial nephritis. This case is remarkable for its exceptionally long and unusual latency period, which generally manifests within days to months in other patients.  After initiating corticosteroid therapy, the patient experienced partial renal recovery and stabilization of renal function during follow-up, highlighting the potential role of immunological mechanisms in delayed renal injury.  This study underscores the need for long-term renal monitoring in patients treated with BCG immunotherapy.