IgG4-related disorder of the retroperitoneum resembling Castleman's disease plasma cell type: a report of 2 cases.

This study reports 2 cases of IgG4-related disorder of the retroperitoneum resembling plasma cell type of Castleman's disease. A single lesion was located in the renal hilum and ureter, respectively, in these 2 cases. Histologically, both lesions were characterized by reactive follicular hyperplasia with active germinal centers and a sheet of polyclonal mature plasma cells in the interfollicular area. The prominent sclerosis and/or fibrosis, which were characteristic histological findings of IgG4-related disorders, were absent. However, immunohistochemical study demonstrated numerous IgG4+ plasma cells accounting for more than 50% of IgG+ cells. The phlebitis that occurs with early lesions of obliterative phlebitis is one of the characteristic histological findings of IgG4-related disorders and was noted in one case. Serum IgG4 concentration was increased in one case. The serum interleukin-6 level was within the normal range in one case that was examined. From a therapeutic perspective, it is important to discriminate IgG4-related disorder from plasma cell type of Castleman's disease.