Bucillamine-induced membranous nephropathy versus primary membranous nephropathy: comparing pathological features and kidney prognosis.

To evaluate the pathological and clinical course differences between bucillamine‑induced membranous nephropathy (BCL-MN) and primary membranous nephropathy (p-MN). This retrospective cohort study included 29 BCL-MN patients and 98 p-MN patients at two hospitals from 2000 to 2019. We compared the kidney biopsy findings and clinical course between the BCL-MN and p-MN groups, focusing on pathological differences, proteinuria relapse rates, and 30% or greater decrease in the eGFR. While kidney function and proteinuria levels were similar, histopathological differences were observed. BCL-MN group showed less spike formation in LM and more stage I cases. IgG1 was predominant in BCL-MN group, contrasting with IgG4 in p-MN group. BCL-MN group had significantly higher prevalence of segmental subepithelial deposits (66.7% vs. 24.7%, p < 0.001) and para-mesangial deposits (61.5% vs. 18.1%, p < 0.001). Notably, foot process effacement in areas without dense deposits was more common in BCL-MN (96.3% vs. 4.6%, p < 0.001). Clinically, the majority of patients in the BCL-MN group experienced proteinuria resolution after 1 year of drug discontinuation alone, and there was no progression of renal function decline. BCL-MN differs from p-MN both histologically and clinically, which may be related to the mechanism induced by BCL.