Primary Membranous Nephropathy With Enhanced Staining of Exostosin 1/Exostosin 2 in the Glomeruli: A Report of 2 Cases

Technological advances have allowed the discovery of 6 subtypes of membranous nephropathy based on target antigens: M-type phospholipase A(2) receptor (PLA(2)R), thrombospondin type 1 domain-containing 7A (THSD7A), neural epidermal growth factor-like 1 protein, semaphorin 3B, exostosin 1 (EXT1), and EXT2. EXT1/EXT2 are thought to be associated with secondary (autoimmune) membranous nephropathy. Although it has been reported that PLA(2)R- and THSD7A-associated membranous nephropathy have rarely been detected concomitantly, there have been no previous reports demonstrating PLA(2)R- or THSD7A-associated membranous nephropathy with enhanced glomerular staining of EXT1/EXT2. We describe 2 cases of primary membranous nephropathy with enhanced glomerular staining of EXT1/EXT2. Patient 1 was diagnosed with PLA(2)R-associated primary membranous nephropathy, and patient 2 was diagnosed with THSD7A-associated primary membranous nephropathy. Both patients achieved clinical remission in response to immunosuppressive therapy. Neither patient demonstrated signs of autoimmune diseases, and antinuclear antibodies were absent in their sera. Based on these 2 cases, enhanced staining of EXT1/EXT2 in glomeruli, although rare, can be detected in primary membranous nephropathy without autoimmune diseases.