Clinical features and outcomes of immunoglobulin G4-related kidney disease and immunoglobulin G4-related retroperitoneal fibrosis in Korea

Immunoglobulin G4 (IgG4)-related disease (RD) is a newly recognized disease, and a few epidemiologic studies about this disorder have been published. This research aimed to demonstrate the clinical features and outcomes of IgG4-related kidney disease (RKD) and IgG4-related retroperitoneal fibrosis (RPF) compared to other organs' involvement. Patients who were diagnosed with IgG4-RD from January 2009 to July 2019 at three medical institutions in South Korea were included. They were classified into three groups: RKD, RPF, and Others groups. The differences in symptoms, laboratory, histological and radiological findings, treatment, and outcomes among the three groups were evaluated. Of 94 patients, 13 (13.8%) and 22 patients (23.4%) were classified into the RKD and RPF groups, respectively. There were older (p = 0.004) and more asymptomatic patients (p = 0.02) in the RKD and RPF groups. In the RKD group, hypocomplementemia (p = 0.003) and eosinophilia (p = 0.001) were more frequently identified. In logistic regression analysis, hypocomplementemia (odds ratio [OR], 14.04; 95% confidence interval [CI], 1.38-142.95) and decreased renal function at the time of diagnosis (OR, 0.95; 95% CI, 0.91-0.98) were associated with renal involvement. Older age (OR, 1.05; 95% CI, 1.00-1.11), male (OR, 6.11; 95% CI, 1.41-26.61), and higher serum IgG4 levels (OR, 1.00; 95% CI, 1.00-1.00) were associated with retroperitoneal involvement. The treatment duration was longer in the RKD and RPF groups (p = 0.01) with glucocorticoids. Renal and retroperitoneal involvement in IgG4-RD presented clinical features that distinguish it from other organs' involvement, such as incidental diagnosis, hypocomplementemia, eosinophilia, and the need for a longer duration of maintenance treatment.