Recurrent IgG4 Disease-Related Tubulointerstitial Nephritis Treated With Rituximab As Maintenance Therapy.

Immunoglobulin G4-related disease (IgG4-RD) is a rare chronic immune-mediated multisystem disease with renal manifestations of tubulointerstitial nephritis (IgG4-TIN) and membranous nephropathy (IgG4-MN). IgG4-RD and its sequelae are treated with immunosuppressive therapy, including steroids and rituximab (RTX), which have demonstrated high efficacy in achieving disease remission. We describe a patient who was diagnosed with pancreatitis secondary to IgG4-RD through laboratory and imaging studies. Despite being on RTX, he developed acute kidney injury (AKI) and was diagnosed with IgG4-TIN via kidney biopsy. He was treated with prednisone and RTX, and his symptoms and renal function improved. Despite RTX reaching peak efficacy 6 months after administration, our patient had a breakthrough IgG4-TIN during this period. This case highlights the importance of maintaining a high index of suspicion for renal involvement (IgG4-TIN or IgG4-MN) in patients with AKI superimposed on IgG4-RD, and that maintenance therapy with RTX retreatment was associated with longer relapse-free survival at 12 months of follow-up. Our patient had no severe infections or hypogammaglobulinemia (≤5 g/l) with RTX, confirming RTX's safety and efficacy in maintenance remission therapy for recurrent IgG4-TIN.