IgG4-related tubulointerstitial nephritis with membranous nephropathy

We describe a 67-year-old woman who presented with significant proteinuria and hematuria. Kidney biopsy showed immunoglobulin G4 (IgG4)-related tubulointerstitial nephritis (TIN) with concurrent membranous nephropathy. IgG4-related TIN is a recently described entity that presents with progressive decreased kidney function and is characterized by a plasma cellrich infiltrate that is positive for IgG4. It is associated with patchy, often well-localized, tubular atrophy and interstitial fibrosis. Workup for circulating antiphospholipase A₂ receptor antibodies was negative, suggesting that the membranous nephropathy was not "primary" and may be linked to the IgG4-related disease. The presence of significant proteinuria and hematuria in the setting of IgG4-related TIN should raise suspicion of a glomerular disease. It is important to correctly diagnose IgG4-related TIN and concurrent membranous nephropathy because the lesion responds well to steroid therapy.