Azathioprine as successful maintenance therapy in IgG4-related tubulointerstitial nephritis

A 65-year-old man presented with a progressive increase in plasma creatinine (PCr). Two years before, diffusion-weighted magnetic resonance imaging had revealed a relapse of immunoglobulin G4 (IgG4)-related autoimmune pancreatitis (AIP) associated with sclerosing cholangitis. Bilateral hypointense renal cortical nodules were also described. Kidney biopsy showed patchy disappearance of tubules, sparse interstitial fibrosis and IgG4+ plasma cells (>30 per high power field) leading to the diagnosis of IgG4-related tubulointerstitial nephritis (TIN). Despite methylprednisolone, PCr and serum IgG4 levels remained elevated. Starting azathioprine (AZA) normalized IgG4 levels, which elicited corticosteroid withdrawal after 17 months. One year later, renal function remains stable. Our clinical observation underlines the importance of biological and radiological long-term follow-up of patients with previous AIP in order to early detect IgG4-related renal involvement. Corticosteroids are the first choice, but in the case of adverse effects or partial remission, AZA could be a useful and safe alternative therapy.