A Case of Immunoglobulin G4-related Tubulointerstitial Nephritis with Simultaneous Resolution of Plasma Cell Infiltration and Fibrosis after Steroid Treatment.

We performed 3 kidney biopsies in a 71-year-old man. At the first biopsy, we made the diagnosis of immunoglobulin G4 (IgG4)-related interstitial nephritis characterized by the simultaneous presence of IgG4-positive plasma cells and characteristic fibrosis with a bird's-eye pattern. At the second biopsy, rather than finding fibrosis as a post-inflammatory scar, we noted that steroid treatment had caused the simultaneous disappearance of IgG4-positive plasma cells and fibrosis and had restored the normal tubular structure. The third biopsy showed the recurrence of the disease with inflammatory cells accompanied by fibrosis. These findings suggest that IgG4-positive plasma cells and fibrosis occur simultaneously.