Not a Minimal Change: IgG4 to Minimal Change Disease (MCD) in a Kidney Transplant Recipient

Introduction: Progressing to end-stage renal disease due to an IgG4 disease is rare but development of Minimal-Change Disease on a transplanted kidney is even more uncommon. We report a patient with non-nephrotic proteinuria diagnosed with MCD. Case Description: A 74-years-old male patient with ESRD due to biopsy proven IgG4 tubulointerstitial nephritis, who received a living donor kidney transplant from his son, develops non-nephrotic range proteinuria of 1-1.5g/d three years post transplant with stable creatinine of 0.7 and GFR of 94ml/min/1.732. Pre-transplant cPRA was 0%, no delayed graft function and post transplant course was uncomplicated. At presentation he was asymptomatic. The urinalysis was only remarkable for proteinuria without casts. He does not take NSAIDs, and uses acetaminophen occasionally for pain. Further workup did not find abnormalities in serum: IgG4, K/L ratio, SPEP, BK virus, C3, C4, or tacrolimus levels. The patient has a diagnosis of type 2 diabetes mellitus but has always been well controlled, with current A1C 6.5%. Initial treatment plan included the start of SGLT2 inhibitors, and optimizing an existing ARB. Persistent unexplained proteinuria prompted a kidney allograft biopsy. The biopsy was reviewed by the USA Joint Pathology Center: 21 glomeruli, 0 of which were globally sclerosed and <10% IFTA, under light microscopy. No abnormalities found on 8 glomeruli under immunofluorescence. Electronic microscopy found diffuse effacement of foot processes. The biopsy was consistent with Minimal Change Disease glomerulopathy. Discussion: Literature review found very few case reports of newly developed Minimal Change Disease in transplanted kidneys, and specifically none in a patient with ESRD from IgG4 disease. Many of the case reports had low glomeruli counts in their biopsies, which raises the possibility of missed FSGS. Our biopsy contained over 20 glomeruli, strongly indicating MCD. Our patient does not have a clear risk factor for developing MCD and did not have nephrotic range proteinuria. We are in a patient centered discussion about treatment paths, which include stress doses steroids, and alternative immunotherapies. This case highlights the importance of allograft biopsies as part of a thorough post transplant follow up, so that treatments can be tailored to address unexpected pathology.