Objective Recently, a new concept of IgG4-related systemic disease including autoimmune pancreatitis, characterized by a high serum IgG4 level and tissue infiltration by IgG4-positive plasma cells, has been proposed. Our aim was to investigate the renal involvement in this condition.
Patients and Methods We investigated the results of laboratory and imaging studies of the kidneys in 7 patients with IgG4-related systemic disease, and examined the renal histology in four of them. All patients showed elevated serum IgG4 levels, and 4 had autoimmune pancreatitis. The other three patients showed involvement of various extrapancreatic organs (lymphadenopathy, sialadenitis or renal insufficiency), and abundant IgG4-positive plasma cell infiltration was confirmed in their affected tissues.
Results Six of the 7 patients showed some renal abnormalities. In one patient, hydronephrosis was observed accompanied by retroperitoneal fibrosis. Another patient showed multiple low-density areas in both kidneys by computed tomography, and gallium citrate scintigraphy showed gallium-67 accumulation in both kidneys, although renal function was normal. Four patients had tubulointerstitial nephritis. In two of them, the tubulointerstitial nephritis was diffuse. In one patient, marked diffuse but patchily distributed lymphoplasmacytic infiltration of the renal interstitium was observed. In another patient, computed tomography showed a tumor-like low-density mass; open biopsy of the mass showed aggregates of lymphocytes and plasma cells in the renal interstitium.
Conclusion Renal parenchymal lesions in IgG4-related systemic disease are due to dense lymphoplasmacytic infiltration of the renal interstitium, and the lesions vary from diffuse tubulointerstitial nephritis to tumor-like masses according to the distribution patterns of the infiltrating cells.