Isolated testicular immunoglobulin G4-related disease mimicking malignancy: a rare case report.

Background: Immunoglobulin G4-related disease (IgG4-RD) is a systemic fibroinflammatory disorder that can involve virtually any organ; however, isolated testicular disease remains exceptionally rare. Its ability to mimic malignancy, both clinically and radiologically, frequently results in an unwarranted orchiectomy. Case presentation: We report a 49-year-old man from eastern Nepal who presented with a 3-day history of painless right testicular swelling. Examination revealed a firm, non-tender mass with normal serum tumor markers (beta-human chorionic gonadotropin, alpha-fetoprotein, and lactate dehydrogenase). Scrotal ultrasonography demonstrated multiple hypoechoic lesions without internal vascularity, raising suspicion for malignancy. A right high inguinal orchiectomy was performed. Histopathological evaluation revealed dense lymphoplasmacytic infiltration, storiform fibrosis, and a predominance of IgG4-positive plasma cells (40-45%), confirming IgG4-related disease of the testis. The postoperative course was uneventful. Discussion: This case exemplifies the diagnostic challenge posed by isolated testicular IgG4-RD, a benign yet deceptive entity that can be misinterpreted as testicular cancer. Despite characteristic radiological features and normal tumor markers, clinical suspicion for malignancy often drives unnecessary surgery. Recognition of IgG4-RD in the differential diagnosis is essential, as timely medical therapy with corticosteroids can achieve remission and preserve the testis. Conclusion: Isolated testicular IgG4-RD should be considered in patients presenting with painless testicular enlargement and normal tumor markers. Early identification and appropriate immunopathological evaluation may help avoid unnecessary orchiectomy and facilitate individualized management, including surveillance or immunosuppressive therapy, depending on disease extent and clinical activity.