A case of immunoglobulin G4-related disease with a urethral lesion diagnosed by radiological imaging before biopsy.

We present a 50-year-old female with IgG4-related disease (IgG4-RD) of the urethra. She had been diagnosed with IgG4-RD involving the pancreas, lacrimal glands, salivary glands, kidneys, and right breast 5 years earlier, which had remitted after steroid treatment. In recent months, she had experienced urinary incontinence. Her local physician noted a urethral stricture. Magnetic resonance imaging (MRI) showed a lesion surrounding the urethra, with a slightly high signal intensity on T2-weighted and short-term inversion recovery images, and a mildly high signal intensity on diffusion-weighted images. Accordingly, IgG4-RD involving the urethra was suggested. Her serum IgG4 level was slightly elevated at 127 mg/dL, which is below the normal upper limit of 135 mg/dL. A transurethral biopsy revealed significant lymphocytic and IgG4-positive plasma cell infiltrates (50-80/high-power field), fibrosis, and obstructive phlebitis. Thus, IgG4-RD of the urethra was confirmed. A systematic search including CT and MRI did not reveal any new gross lesions. Steroid therapy improved her symptoms within a few days. Follow-up MRI revealed shrinking of the urethral lesion and lower signal intensity on T2-weighted images. IgG4-RD with urethral lesions is extremely rare. No cases of diagnosis of IgG4-RD urethral lesions based on MRI findings before biopsy have been reported to date. When a middle-aged woman presents with uniform circumferential urethral lesions, IgG4-RD should be considered in the differential diagnosis. Here, we report detailed imaging findings and radiological differential diagnoses, and discuss relevant literature.