Membranous nephropathy in Kimura disease: A case report and literature review on renal biopsy findings.

Kimura disease (KD) is a chronic benign granulomatous disease. Approximately 20% of patients with KD have renal disease. Membranous nephropathy (MN) is one of the main renal pathologies in KD; however, the underlying mechanism remains unknown. We herein present a 28-year-old male diagnosed with KD after biopsy of a left lower eyelid mass 11 years earlier. He visited our hospital with edema in the lower legs and scrotum. A blood test showed a serum creatinine level of 0.95 mg/dL and serum albumin level of 0.9 g/dL. Urinalysis revealed heavy proteinuria with mild hematuria. Renal biopsy showed spike formation by PAM staining and granular deposits of IgG and C3 in the glomerular basement membrane by direct immunofluorescence microscopy (IF). Electron microscopy revealed subepithelial electron-dense deposits (EDD). IF staining for the phospholipase A2 receptor (PLA2R) was positive in the glomerular basement membrane, leading to a diagnosis of PLA2R-associated MN. Our literature review on MN in KD included 14 cases, all of which exhibited subepithelial EDD, while subendothelial EDD was absent in 10. PLA2R staining was positive in 2 of the 3 cases examined. The results of this case and the literature review suggest the involvement of autoantibodies against podocyte antigens in the pathogenesis of MN in KD. Further studies are needed on these antigens.