Differences of clinicopathological features between IgG4‐related and non‐IgG4‐related idiopathic retroperitoneal fibrosis

To evaluate the clinical and pathological features of IgG4-related and non-IgG4-related idiopathic retroperitoneal fibrosis (IRF) according to the latest classification criteria for IgG4-related disease in 2019.Patients with IRF confirmed by histological examination from our hospital between 2000 and 2020 were selected in this study. Medical records of all patients were reviewed by independent researchers. Retroperitoneal specimens were obtained for hematoxylin & eosin staining, elastic-collagenous fiber staining, and immunohistochemical analysis. The clinical and pathological features between IgG4-related and non-IgG4-related IRF were analyzed.A total of 105 patients were included with 77 in the IgG4-related group and 28 in non-IgG4-related group. The ratio of male to female patients and the incidence of acute renal failure were significantly higher in the IgG4-related group than in the non-IgG4-related group. Elevated erythrocyte sedimentation rate and C-reactive protein were more common and the recurrence rate was significantly higher in the IgG4-related group than in the non-IgG4-related group. Radiographically, the ureter was more easily involved by retroperitoneal soft tissue in the IgG4-related group. Histologically, there were no significant differences in the incidence of dense lymphoplasmacytic infiltration, storiform fibrosis, and obliterative phlebitis between the two groups except for the IgG4 staining.Idiopathic retroperitoneal fibrosis can be classified into IgG4-related and non-IgG4-related subtypes. There were no significant pathological differences between the two subtypes of IRF, except for the IgG4 staining. Patients with the IgG4 subtype tended to be more likely to be male, have a higher inflammatory index, and be more likely to have recurrence.