Bladder Cancer versus Hemorrhagic Cystitis: A Case of Mistaken Identity in a 34-Year-Old Male Undergoing Therapy for Granulomatosis with Polyangiitis.

A 34-year-old male was referred for management of bladder cancer noted on workup for gross hematuria and new-onset irritative voiding symptoms. The patient's history was significant for recently diagnosed granulomatosis with polyangiitis for which he was undergoing treatment with oral cyclophosphamide and corticosteroids. Cystoscopy revealed lesions suspicious for malignancy, but the patient was diagnosed with hemorrhagic cystitis secondary to BK virus infection upon cytology review, and immunostaining confirmed a polyomavirus infection of the urothelium. The patient's symptoms resolved after a modification of his immunosuppressive regimen, and antiviral therapy was ultimately unnecessary. Though symptomatic BK virus infection of the genitourinary tract is common in immunosuppressed transplant patients, its occurrence in a patient undergoing immunomodulation for an autoimmune disease has not been reported yet. This case illustrates the potential for active BK virus infections in atypical patient populations and underscores the importance of rigorous hematuria workup, particularly in patients with multiple risk factors.