[IgG4-related prostatitis associated with retroperitoneal fibrosis: a case report].

A 70-year-old male was referred to our hospital because of an abnormally high prostate specific antigen (PSA) level (4.4 ng/ml) associated with lower urinary tract symptoms. Needle biopsy of the prostate did not reveal any malignant tissue. Four months later, the patient presented again with hydronephrosis, which was diagnosed using ultrasonography. Furthermore, contrast-enhanced computed tomography (CT) and magnetic resonance imaging (MRI) revealed left hydronephrosis caused by a soft tissue mass around the left iliac artery compressing the left ureter. Serum IgG4 level was 918 mg/dl. On immunohistochemical reevaluation of the prostate biopsy specimens, the samples were positive for IgG4 immunostaining. The patient was finally diagnosed with IgG4-related prostatitis with retroperitoneal fibrosis. With steroid therapy, the hydronephrosis and urinary symptoms were ameliorated. Our experience with this case suggests that in a male patient with urinary symptoms, biopsy of the prostate may be useful for exact diagnosis when IgG4-related disease is suspected.