The possible involvement of immunoglobulin G4 (IgG4) in the pathogenesis of idiopathic sclerosing lesions has been suggested. In this study, a clinicopathologic analysis was performed to reveal characteristics of retroperitoneal fibrosis relating to IgG4. The study involved 17 patients with retroperitoneal fibrosis. Immunohistochemistry revealed numerous IgG4-positive plasma cell infiltrates in 10 cases (IgG4-related), but only a few positive cells in 7 cases (non-IgG4-related). All patients with IgG4-related retroperitoneal fibrosis were male, whereas all except 1 with unrelated lesions were female. Histologically, eosinophilic infiltration (>5 cells per high-power field) and obliterative phlebitis were commonly observed in IgG4-related lesions. Serologically, serum IgG and IgG4 concentrations were significantly higher in the IgG4-related cases, with the IgG4 concentrations all over 135 mg/dL (the upper limit of the normal range). Steroid therapy was performed in 13 cases, and was effective irrespective of IgG4. Three patients had recurrence during the follow up. Five of 10 IgG4-related cases had sclerosing lesions at other sites. The only tests that reliably distinguish the 2 groups were serum IgG4 levels or IgG4/IgG ratio in the plasma cells in a tissue biopsy. The only major clinical difference was the striking male predominance in IgG4-related cases. In conclusion, this study revealed that retroperitoneal fibrosis could be classified as IgG4-related or not. This distinction seems important to help better characterize the biology/pathogenesis of both groups and better predict the possibility of other IgG4-related processes at other anatomic sites.
Inflammatory abdominal aortic aneurysm (AAA) is a member of a family of disorders referred to as "chronic periaortitis" together with retroperitoneal fibrosis. Retroperitoneal fibrosis is included in IgG4-related disease, which is characterized by numerous infiltrating IgG4-positive plasma cells and high serum IgG4 concentrations. However, the relationship between IgG4-related disease and inflammatory AAA has not been documented. In this study, we examined the clinicopathologic characteristics of inflammatory (10 cases) and atherosclerotic (22 cases) AAAs, based on the hypothesis that inflammatory AAA might be related to IgG4-related disease. Cases of inflammatory AAA could be classified into 2 groups based on immunostaining of IgG4. Four patients showed diffuse infiltration of abundant IgG4-positive plasma cells (IgG4-related cases), whereas the remaining 6 cases of inflammatory AAA and all cases of atherosclerotic AAA had only a few IgG4-positive plasma cells (non-IgG4-related cases). IgG4-related inflammatory AAA was pathologically characterized by the frequent infiltration of eosinophils, lymph follicle formation, perineural inflammatory extension, and inconspicuous infiltration of neutrophils compared with non-IgG4-related inflammatory AAA. Obliterative phlebitis, which is venous occlusion with inflammatory cell infiltration, is observed in all IgG4-related cases. In addition, serum IgG4 concentrations were significantly higher in IgG4-related inflammatory AAA (109 to 559 mg/dL, normal range: 4 to 110 mg/dL) than non-IgG4-related inflammatory AAA (32 to 59 mg/dL) and all atherosclerotic AAA (12 to 83 mg/dL). In conclusion, inflammatory AAAs might be classified into 2 groups: IgG4-related or nonrelated. The former might be one of the IgG4-related diseases, and could be included in IgG4-related periaortitis together with retroperitoneal fibrosis.
Recognizing a new disease entity of IgG4-related IAAA seems important because this was clinically and pathologically different from conventional aAAA and non-IgG4-related IAAA.
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