A case of membranous nephropathy characterized by atypical distribution of phospholipase A2 receptor

A 77-year-old man was referred to our hospital with persistent proteinuria and progressive lower leg edema. Past history was unremarkable except for hypertension. Autoimmune diseases, infections, and malignancies were excluded based on clinical and laboratory test results. Renal biopsy specimens showed membranous nephropathy with segmental distribution of spikes and bubbling appearance. Double contour formation in glomerular tufts was also observed. There were no proliferative changes in the glomeruli. Interstitial fibrosis and tubular atrophy were moderate, and no interstitial inflammation was observed. Arteries showed moderate sclerotic changes with hyalinosis. Immunohistochemical analysis revealed no thrombospondin type 1 domain-containing 7A reactivity. Immunofluorescence staining showed segmental granular positivity of IgG on glomerular tufts and focal staining of IgG on the tubular basement membranes. IgG deposits (subclass distribution: IgG1, 2+; IgG2, -; IgG3, 1+; IgG4, 2+) and phospholipase A2 receptor type 1 (PLA2R1) immunoreactivity showed similar distributions in both glomeruli and renal tubular basement membranes. Electron microscopy revealed subendothelial edema in partially collapsed glomemlus. No subepithelial dense deposits were observed in the glomeruli under an electron microscope. This is the first documented case of membranous nephropathy (MN) with segmental distribution of PLA2R1 in the glomeruli and focal PLA2R1 positivity in renal tubular basement membranes. Our findings extend the pathological presentation of PLA2R1-associated MN. Future studies are required to examine the mechanistic insights of these atypical histopathological features.