Immunoglobulin G4-related disease mimicking multiple myeloma

Immunoglobulin G4-related disease (IgG4-RD) is a rare, poorly understood immune mediated disorder. It is characterized by a wide clinical spectrum depending on the organs affected. Serum IgG4 may be elevated, but this is not mandatory. Imaging abnormalities are usually detected in the affected organs, which typically show enlarged dimensions. Definitive diagnosis is made upon tissue biopsy demonstrating lymphoplasmacytic infiltration with predominance of polyclonal IgG4-positive plasma cells, storiform fibrosis and obliterative phlebitis. The most common renal manifestations [(IgG4-related kidney disease (IgG4#8209;RKD)] include tubulointerstitial nephritis, membranous glomerulonephritis and pyelitis. There is, usually, good therapeutic response to corticosteroids, but rituximab may be needed in cases of relapsing or resistant disease. A diagnostic challenge, and because it diagnosis needs specific immunohistochemical staining techniques, IgG4-RKD should be contemplated in the differential diagnosis of obscure kidney disease in order not to be missed.