IgG4-related sclerosing mesenteritis: a rare mesenteric disease of unknown etiology.

Sclerosing mesenteritis is a rare inflammatory and fibrosing disorder of unknown etiology, while IgG4-related disease (IgG4-RD) consists of mass-forming, fibroinflammatory lesions characterized by high serum IgG4 levels and tissue infiltration of many IgG4-positive plasma cells; obliterative phlebitis is common. This report describes a case of sclerosing mesenteritis that was considered a manifestation of IgG4-RD. A 53-year-old man underwent right hemicolectomy because of an ileocecal mass that did not improve with conservative therapy. The ill-defined fibroinflammatory lesion extended in the mesentery with storiform fibrosis, obliterative phlebitis, and infiltration of many IgG4-positive plasma cells. The ratio of IgG4-positive/IgG-positive cells was 64%, and the ratio of forkhead box protein 3 (FOXP3)-positive/CD4-positive cells was elevated (13%). It is likely that at least some cases of sclerosing mesenteritis are a manifestation of IgG4-RD. It is important to investigate this relationship because steroid therapy may benefit such cases.