Membranous-like glomerulopathy with monoclonal immunoglobulin deposits in a patient with class V lupus nephritis: a case report and literature review

Patients who have lupus nephritis are usually asymptomatic. A few lupus nephritis patients may experience edema, hypertension, nocturia, polyuria, and foamy urine. Foamy urine or nocturia are early indicators of proteinuria, indicating tubular or glomerular dysfunction. Membranous-like glomerulopathy with masked IgG kappa deposits (MMMD) represents a form of immune complex deposition marked by concealed IgG kappa-restricted deposits, which are located in the subepithelial and mesangial areas as seen on electron microscopy. We report a rare case of a 26-year-old Hispanic woman with a history of systemic lupus erythematosus (SLE) diagnosed in 2015, who was initially evaluated for proteinuria and underwent a renal biopsy in 2019. The biopsy demonstrated membranous glomerulonephritis consistent with class V lupus nephritis. The patient volunteered to participate in a clinical trial for lupus nephritis in mid-2023. The second renal biopsy done at this visit (4 years after the initial renal biopsy) reported membranous glomerulonephritis, consistent with lupus class V and MMMD. Given the new finding of MMMD, a search for monoclonal gammopathy was initiated by looking for flow cytometry, serum protein electrophoresis (SPEP), and serum-free light chains, all of which were reported as negative. As the workup for monoclonal gammopathy and monoclonal gammopathy of renal significance (MGRS) was negative, MMMD was considered a secondary manifestation of lupus nephritis, a rare renal presentation of the condition.