Immunoglobulin G4-related tubulointerstitial nephritis: A not to be missed diagnosis.

Immunoglobulin G4-related tubulointerstitial nephritis (IgG4-TIN) is a newly recognized clinicopathological entity characterized by a dense interstitial infiltrate of IgG4-positive plasma cells accompanied by fibrosis and obliterative phlebitis causing acute or chronic renal dysfunction amenable to corticosteroid therapy. IgG4-TIN is the dominant manifestation of renal involvement in IgG4-related disease (IgG4-RD) which is a novel, immune-mediated, fibroinflammatory and multiorgan disorder. We describe a case of IgG4-TIN with isolated renal involvement in an elderly male patient with poor response to corticosteroid therapy. The distinctive serological, histopathological, and ultrastructural features of this condition which can facilitate differential diagnosis of TIN are highlighted to emphasize the need for early diagnosis and preservation of kidney function.