IgG4-producing lymphoma arising in a patient with IgG4-related disease.

We herein report a case in which an IgG4-producing lymphoma arose in a patient with a previous diagnosis consistent with an IgG4-related disease. A 43-year-old man presented with enlarged cervical lymph nodes and was treated with steroids and radiation for what was initially assumed to be Kimura's disease, although the lesions were later histologically re-diagnosed as IgG4-related lymphadenopathy. Fourteen years later, when the patient was 58-years-old, he presented with retroperitoneal fibrosis and swollen lymph nodes. The suspicious lesions were not histologically examined as the patient did not give consent. However, the serum IgG4 concentration was high (1400 mg/dL) and he was clinically diagnosed with systemic IgG4-related disease. Although steroid administration reduced the size of the lesions, tapering the dose finally resulted in systemic, prominently enlarged lymph nodes. Analysis of the biopsy specimen revealed that these multiple lymph node lesions were marginal zone B cell lymphomas that themselves expressed IgG4. Complete remission was achieved after a total of six courses of chemotherapy including rituximab. This case suggests that the infiltrating IgG4-expressing cells observed in IgG4-related disease can clonally expand to malignant lymphomas.