Atypical Polypoid Bladder Lesion Mimicking Urothelial Carcinoma in a Young Male: A Case Report About a Possible Autoimmune-Triggered Granulomatous Inflammation With Secondary Colonization.

Gross hematuria is a critical clinical symptom requiring thorough diagnostic evaluation, particularly due to its association with urothelial carcinoma. However, other differential diagnoses must also be considered, including renal carcinoma, infection, urolithiasis, and autoimmune disease. We report the case of a 28-year-old male presenting with gross hematuria, flank pain, and dysuria. Imaging revealed bladder wall thickening and bilateral narrowing of the renal pelvis. Cystoscopy showed a large, polypoid lesion suggestive of urothelial carcinoma. Transurethral resection (TUR-B) was performed; however, histological analysis revealed granulation tissue with inflammatory infiltrates, multinucleated giant cells, and necrosis but no evidence of malignancy. Metagenomic sequencing identified Peptoniphilus sp. SAHP1, Anaerococcus mediterraneensis, and Trichomonas vaginalis, though their pathogenic role remained uncertain. Shortly after, the patient developed systemic inflammatory symptoms, including exanthema and gingivostomatitis. Biopsy of skin lesions showed leukocytoclastic vasculitis, and serologic testing yielded borderline myeloperoxidase-specific antineutrophil cytoplasmic antibody (MPO-ANCA) positivity. Under corticosteroid therapy, all symptoms, including the bladder lesion, regressed completely. This case highlights a rare constellation of findings mimicking urothelial carcinoma, ultimately pointing to a probable autoimmune vasculitic process with possible secondary microbial colonization. It underscores the diagnostic challenges posed by atypical presentations and the need for integrative interpretation of clinical, histological, and molecular findings in complex cases.