Retroperitoneal Fibrosis in Chronic Kidney Disease

We report two cases of retroperitoneal fi brosis that emerged during a clinical course of moderate chronic kidney disease. In both cases, we observed an elevation in the serum CRP and IgG4 levels without an increase in the white blood cell count. The patients were treated with prednisolone. Their clinical conditions improved with a decrease in the serum IgG4 to total IgG ratio. The present cases suggest the importance of a differential diagnosis of retroperitoneal fi brosis in the medical care of chronic kidney disease patients, and we propose a useful biomarker for retroperitoneal fi brosis, which we suspect is associated with IgG4-related disease.