Secondary Membranous Lupus Nephritis Presenting with Bilateral Renal Vein Thrombosis: A Diagnostic and Therapeutic Challenge

Introduction: Membranous glomerulonephritis (MGN) is a common cause of nephrotic syndrome in adults. While most cases are idiopathic, autoimmune conditions like systemic lupus erythematosus (SLE) can cause secondary MGN, specifically Class V lupus nephritis. The nephrotic state, combined with lupus-related endothelial injury and vasculitis, increases the risk of venous thromboembolism, including renal vein thrombosis (RVT), a rare but serious complication. Case Description: A 46-year-old woman with a history of lupus nephritis diagnosed in adolescence, previously treated with high-dose steroids and cyclophosphamide, presented with worsening renal function and new left leg swelling. Her history included antiphospholipid syndrome and pulmonary embolism requiring suprarenal IVC filter placement. Serologic workup revealed high-titer ANA (1:2560) and positive anti-dsDNA, anti-Smith, RNP, and SSA antibodies. Kidney biopsy confirmed membranous nephropathy consistent with Class V lupus nephritis. She had been on mycophenolate and had received rituximab; prednisone was tapered. Her creatinine worsened from 0.8 to over 3 mg/dL. Duplex ultrasound showed extensive DVT in the left leg. CT revealed a thrombus below the IVC filter, and bilateral RVT was confirmed by ultrasound. She was started on a heparin drip and transitioned to warfarin. She remained hemodynamically stable and did not require vascular intervention. Discussion: While RVT is typically associated with primary MGN, this case shows that secondary MGN from lupus can present with bilateral RVT. The presence of an IVC filter may have contributed to venous stasis and clot propagation. Timely imaging helped define the thrombus burden and excluded complications like phlegmasia. Despite extensive clotting, the patient was successfully managed with conservative therapy including immunosuppression and anticoagulation.