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Background A subset of patients without overt systemic lupus erythematosus (SLE) present with biopsy findings typically seen in lupus nephritis (LN). Although a minority eventually develops SLE, many do not. It remains unclear how to classify or treat these patients. Our study attempted to further understand the clinical and pathological characteristics of cases with lupus-like nephritis (LLN). Methods Among 2700 native kidney biopsies interpreted at University of Rochester Medical Center (URMC) from 2010 to 2019, we identified 27 patients with biopsies showing lupus-like features (LL-fx) and 96 with LN. Of those with LL-fx, 17 were idiopathic LLN and 10 were associated with a secondary etiology (e.g., infection/drugs). Results At the time of biopsy, the LLN-group tended to be slightly older (44 vs. 35), male (58.8 vs. 17.7%, p = .041), and Caucasian (47.0 vs. 28.1%, p = .005). Chronic kidney disease was the most common biopsy indication in LLN (21.4 vs. 2.8%, p = .001). Both LN and LLN presented with nephrotic-range proteinuria (mean 5.73 vs . 4.40 g/d), and elevated serum creatinine (mean 1.66 vs . 1.47 mg/dL). Tubuloreticular inclusions (TRIs; p < .001) and fibrous crescents ( p = .04) were more often seen in LN, while more tubulointerstitial scarring was seen in LLN ( p = .011). At mean follow-up of 1684 d (range: 31–4323), none of the LLN patients developed ESRD. A subset of both LN and cases with LL-fx overlapped with other autoimmune diseases. Conclusions Lupus-like pathologic features are seen in a wide array of disease processes. The findings suggest that LLN may be a manifestation of an autoimmune process that overlaps with SLE.

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.

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