LAUSR

INTRODUCTION The pathologic features of membranous lupus nephritis (MLN) are occasionally encountered in secondary membranous nephropathy (sMN) without overt clinical evidence of SLE. Moreover, some sMN with lupus-like features (LL-MN) have a clinical presentation more typical of primary membranous nephropathy (pMN). Based on the confounding clinical and pathologic presentation, it is unclear how to categorize and treat these patients. METHODS We performed immunohistochemical staining for recently discovered target antigens associated with MN -NELL-1, THSD7A, and EXT1/2, and compared the clinicopathologic presentation of patients with LL-MN to those with pMN and MLN. RESULTS From 2015-2020, there were 21 patients with MLN and 99 with MN, of which 59% were diagnosed pMN and 41% sMN. 44% of sMN showed lupus-like features (LL-fx). All LL-MN were negative for PLA2R and NELL1, but 12% were positive for EXT1/2. 50% of LL-MN had an identifiable systemic disease, of which 56% were autoimmune disease (AD) and 44% infection. Compared to pMN, LL-MN had higher incidence of underlying AD (p=0.02). Within pMN, 24% also had LL-fx (LL-pMN), and all but 1 were PLA2R-(78%) or NELL1-positive (15%). Only 5% of pMN had an AD, 66% of which showed LL-fx. Most idiopathic LL-MN were treated and behaved clinically similarly to pMN. There were no differences in outcome in terms of progression towards ESRD or mortality between LL-MN versus pMN and MLN. CONCLUSION LL-MN appears to have a significant association with underlying AD and has a subset showing EXT1/2 positivity, whereas most LL-pMN and idiopathic LL-MN likely represent an atypical pathologic presentation of pMN.