A Rare Case of Hemophagocytic Lymphohistiocytosis Triggered by Intravesical Bacillus Calmette-Guérin (BCG) for Bladder Cancer.

Intravesical bacillus Calmette-Guérin (BCG) therapy is widely used for non-muscle-invasive bladder cancer but can rarely lead to severe systemic complications. Hemophagocytic lymphohistiocytosis (HLH) is a life-threatening hyperinflammatory syndrome characterized by fever, cytopenias, and organ dysfunction. We describe a 63-year-old man who developed HLH after re-induction BCG therapy. He presented with fever, hepatosplenomegaly, pancytopenia, and liver and kidney dysfunction. Laboratory tests revealed hyperferritinemia and elevated soluble interleukin-2 receptor levels. Liver biopsy showed non-caseating granulomas without acid-fast bacilli, and bone marrow biopsy confirmed hemophagocytosis. Urine culture yielded Mycobacterium tuberculosis complex, consistent with prior BCG instillation. Treatment with high-dose corticosteroids, intravenous immunoglobulin, and BCG-active antibiotics resulted in rapid recovery. This case illustrates that HLH is a rare but serious complication of intravesical BCG, and emphasizes the importance of early recognition and combined immunosuppressive and anti-mycobacterial therapy.