Immunoglobulin G4-related disease (IgG4-RD) is a systemic inflammatory disease found in many organs including biliary tract, salivary gland, kidney, and lung. Tubulointerstitial nephritis is the most common renal manifestation, but hematologic involvement of IgG4-RD is rare. Here, we report on a case of a 57-year-old male with IgG4-related interstitial nephritis with bicytopenia, which was initially thought to be systemic lupus erythematosus. He presented with proteinuria, anemia, thrombocytopenia, and low complement levels. Histological findings showed an increased number of IgG4-positive plasma cells (＞200/high power field), and an elevated IgG4/IgG ratio (＞90%). Serum levels of IgG and IgG4 were also increased. This case emphasized the importance of differential diagnosis of IgG4-RD and immune complex glomerulonephritis. (J Rheum Dis 2015;22:401-404)

Keywords: Immunoglobulin G4-related disease, Thrombocytopenia, Anemia, Interstitial nephritis, Hypocomplementemia