Tubulointerstitial nephritis associated with IgG4-related autoimmune disease

Autoimmune pancreatitis is a chronic fibroinflammatory condition primarily affecting the pancreas. Recent accumulating evidence suggested that autoimmune pancreatitis is a systemic autoimmune disease (immunoglobulin G4 [IgG4]-related autoimmune disease) affecting various organs with dense infiltration of IgG4-positive mononuclear cells. Tubulointerstitial nephritis is still a mysterious disease with an unknown cause. We report 2 cases of tubulointerstitial nephritis associated with autoimmune pancreatitis. In these patients, dense infiltrations of IgG4-positive mononuclear cells were observed in renal interstitium, with high serum IgG4 levels. Furthermore, in patient 1, who had sclerosing cholangitis, serum alkaline phosphatase and serum creatinine levels changed synchronously. Steroid therapy was followed by improved renal function and serum IgG4 levels in both patients. Because tubulointerstitial nephritis associated with IgG4-related autoimmune disease shows a favorable response to steroids and the renal dysfunction and pancreatic dysfunction are reversible, awareness of this entity is necessary for early diagnosis and prompt treatment. In addition, these cases support the hypothesis that IgG4-related autoimmune disease could be one cause of tubulointerstitial nephritis.