IgG4-Related Tubulointerstitial Nephritis 20 Years After Kidney Transplant

Introduction: IgG4-related disease is a relatively rare infiltrative condition that can have multiple systemic involvement including the kidneys. This condition is characterized by dense lymphoplasmacytic infiltrates rich in plasma cells often with elevated serum Immunoglobulin G4 (IgG4) levels. The most common renal manifestation is tubulointerstitial nephritis. Histopathological features are highly characteristic in diagnosis regardless of IgG4 serum levels and include dense lymphoplasmacytic infiltrates organized in a storiform pattern, obliterative phlebitis, and eosinophil infiltrates. Recurrent or de-novo IgG4 related kidney disease has rarely been described in clinical literature. Case Description: We describe a case of a 62-year-old male with chronic kidney disease attributed to interstitial nephritis who received a deceased donor kidney transplant 20 years ago. He presented with acute kidney injury with serum creatinine of 4.2 mg/dL (baseline 1.4-1.6 mg/dL). Work up with transplant renal ultrasound, cell free DNA assay, urine culture and BK PCR was negative. Renal allograft biopsy showed severe mixed inflammation with eosinophils, chronic interstitial inflammation with abundant plasma cells and moderate arteriosclerosis. Immunohistochemistry staining for IgG4 was diagnostic. Lab work revealed elevated serum IgG4 level (1467 mg/dl), low complements, sub-nephrotic range proteinuria. These were absent in a previous kidney biopsy. His prior IgG4 and complement levels were normal. He was treated with steroids and scheduled for rituximab as it has shown to improve clinical and serological features of this disease. His creatinine improved to 3.1 mg/dl with improvement in IgG4 levels to 526 mg/dL and normalization of his complement levels with steroids. Discussion: It is unclear if this is a recurrent or de-novo disease. However, despite these uncertainties, treatment with steroids and biological agents poses good outcomes for transplanted kidneys affected by this infiltrative disease.Interstitial inflammatory infiltrates are composed of lymphocytes and clusters of plasma cells, most of which are positive for IgG4 immunohistochemistry