IgG4-related kidney disease: Pathogenesis, diagnosis, and treatment.

IgG4-related disease (IgG4-RD) is a recently recognized multisystem disease characterized by lymphoplasmacytic inflammation and fibrosis in affected tissues that can affect several organs including the kidney, the involvement of which is often manifested by tubulointerstitial nephritis. The pathogenic mechanisms of IgG4-RD are divided into two sections: one focused on potential initiation mechanisms, particularly genetic, and the other on specific pathological pathways. For the specific pathological pathways, cellular immunity, particularly T-cell mediated immunity, has been implicated in the pathogenesis of IgG4-RD. Renal involvement may manifest as an intrinsic IgG4-related kidney disease (IgG4-RKD) or as a consequence of ureteric obstruction from retroperitoneal fibrosis. Intrinsic kidney disease is most commonly a tubulointerstitial nephritis, but may also present with a variety of glomerular lesions, in particular membranous nephropathy. The first-line treatment of IgG4-RKD is steroids. The long-term side effects of corticosteroids including diabetes, relapses, and resistance to corticosteroid therapy have prompted some experts to use immunosuppressive agents such as rituximab. However, the pathogenesis remains poorly understood. As any delay in treatment may result in irreversible renal failure, early diagnosis and appropriate therapy are very important. Randomized studies are needed to confirm the efficacy of immunosuppressants such as rituximab.