IgG4-related disease involving the penis: a rare case report.

Immunoglobulin G4-related disease (IgG4-RD) is a chronic, systemic fibroinflammatory autoimmune disorder characterized by multi-organ involvement, elevated serum IgG4 levels, and dense infiltration of IgG4+ plasma cells. The disease can affect nearly any organ, and its clinical spectrum has continued to expand in recent years; involvement of the genitourinary system has been increasingly recognized, although direct involvement of the male external genitalia is extremely rare. We report a case of a 29-year-old man with IgG4-RD who initially presented with an unexplained penile mass. Clinical evaluation and laboratory testing revealed right inguinal lymphadenopathy along with elevated serum IgG4 and C-reactive protein (CRP) levels. Histopathological examination demonstrated fibrosis and an increased number of IgG4+ plasma cells, confirming the diagnosis of IgG4-RD. The patient received prednisone at 30 mg/day for four consecutive weeks, which resulted in a marked reduction of the lesion and improvement in symptoms, followed by a taper to a maintenance dose of 6 mg/day. During follow-up, no recurrence of symptoms has been observed. This case indicates that IgG4-RD should be considered in patients presenting with unexplained penile masses, and early recognition with multidisciplinary collaboration among urology, pathology, and rheumatology is essential to prevent unnecessary surgical procedures.