[55] Clinicopathologic Features of IgG4-Associated Retroperitoneal Fibrosis

Madelyn Lew, Mollie Carruthers, Arezous Khosroshahi, Robert Hasserjian, John H Stone, G P Nielsen, Vikram Deshpande. Massachusetts General Hospital, Boston, MA

Background: Retroperitoneal fibrosis (RPF) can be divided into idiopathic and secondary cases. Studies have suggested that idiopathic RPF can be classified into cases that are associated with histopathologic features of IgG4-related disease (IgG4-RD) and those that are not. We analyzed previously unclassified cases of RPF to estimate the prevalence of IgG4-RD within this cohort and to compare clinicopathologic features of IgG4-related and non-IgG4-related RPF.
Design: Following chart review, we subclassified 23 RPF cases into idiopathic or secondary categories on the basis of clinical features. Immunohistochemical analysis for IgG4 and IgG was performed on the 22 idiopathic RPF cases with available paraffin blocks. RPF cases were classified as IgG4-related if the IgG4/IgG-positive plasma cell ratio was greater than 40%. Demographic, radiologic, and histologic features were compared between patients with IgG4-related and non-IgG4-related RPF. Statistical analysis was performed using Fisher's exact test or unpaired t-test.
Results: Twelve of 22 (55%) of the idiopathic RPF cases were classified as IgG4-related and 10 (45%) were classified as non-IgG4-related. IgG4-related RPF cases occurred more frequently in men (M:F ratio of 10:2 vs. 4:3), although the difference was not statistically significant. Compared with non-IgG4-related RPF, IgG4-related RPF was more likely to show periaortic involvement (83% vs. 28%, P=0.02), storiform-type fibrosis (83% vs. 28%, P=0.02), and increased eosinophilic infiltration defined as >5 eosinophils per high power field (83% vs. 0%, P<0.001) in association with a plasma cell infiltrate. In the IgG4-related cases, the mean IgG4/IgG ratio was 79%. However, the mean overall number of IgG4-positive plasma cells per high-power field (HPF) was 13, a figure much lower than that generally observed in other organs involved with IgG4-RD.
Conclusions: IgG4-RD accounts for a sizable subset of patients with idiopathic RPF. Both histologic features and immunohistochemical analysis for IgG4 are critical to the diagnosis of IgG4-RD. Findings of plasma cell infiltration, tissue eosinophilia (>5 eosinophils/high power field), and storiform fibrosis suggest the diagnosis of IgG4-RD in RPF. In this context, the IgG4/IgG ratio may be more important in the diagnosis of IgG4-related RPF than the absolute number of IgG4-positive plasma cells/HPF, particularly when extensive fibrosis is the paramount finding.
Category: Bone & Soft Tissue

Monday, March 19, 2012 1:00 PM

Poster Session II # 23, Monday Afternoon


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