IgA Lambda Membranous Nephropathy: A Rare Entity with Diagnostic and Therapeutic Considerations

Membranous Nephropathy (MN) with monoclonal IgA-lambda deposits is exceptionally rare. We describe a case of MN with monoclonal IgA-lambda deposits complicated by delayed renal biopsy and subsequent therapeutic resistance. When the patient underwent kidney biopsy, Stage IV MN was identified by the Ehrenreich–Churg system, characterized by subepithelial deposits fully incorporated into the thickened glomerular basement membrane—features consistent with chronic, "burned-out" disease. Rituximab was initiated as first-line therapy but failed to produce clinical improvement. Because rituximab targets CD20-expressing B cells, its limited efficacy in IgA-mediated processes may reflect the absence of CD20 on mature IgA-secreting plasma cells. Additionally, the advanced Stage IV MN at the time of diagnosis suggests the disease may have progressed beyond the point at which immunosuppression could offer meaningful benefit. This case underscores the challenges of rare glomerular disorders: the critical role of timely renal biopsy, the potential limitations of conventional anti-CD20 therapy in IgA mediated renal disease, and the impact of patient-driven delays on clinical outcomes