Introduction: Monoclonal gammopathy of renal significance (MGRS) is a recently recognized disorder from pathologic M protein causing renal disease and minimal hematologic disease burden. Failure to treat leads to poor outcomes from progression to advanced monoclonal gammopathies and end stage renal disease (ESRD). We present a case of MGRS with immunotactoid glomerulopathy.
Case Report : A 66-year-old female presented in December 2015 with mild granulocytopenia and anemia. Workup revealed serum 0.28 mg/dL IgM kappa monoclonal M-protein and kappa/lambda ratio of 2.23. She underwent surveillance for MGUS. Due to acute kidney injury, peripheral edema and hypertension, nephrology workup was obtained in December 2017. She had nephrotic range proteinuria and hematuria. Urine studies suggested paraproteinemia. Renal biopsy demonstrated immunotactoid glomerulopathy with membranoproliferative glomerulonephritis pattern. Immunofluorescence showed kappa light chain in mesangial and capillary loop, and heavy IgM and moderate C3 staining. Electron microscopy revealed numerous immunotactoid deposits beneath the glomerular basement membrane and mesangium. M-protein burden remained stable. Her bone marrow biopsy was nondiagnostic, however peripheral flow cytometry identified a small CD20+, CD5-, CD10-, CD23-, B-cell population with kappa light chain restriction. Diagnosis was reclassified as MGRS and she was treated with rituximab weekly for four doses. Follow-up demonstrated stability of M-protein and light chains, improvement of AKI and hypertension, but persistent nephrotic range proteinuria. We are planning an additional eight-week course of weekly rituximab. Treatment outcome and further studies are pending.
Discussion: MGRS is a rare monoclonal gammopathy that was formerly subclassified under MGUS. Patients were undertreated due to under-recognition of the disorder and its renal sequalae. Treatment with regimens targeting a plasma cell or B-cell clone can reduce the clone and improve renal outcomes. Our patient experienced a partial response to clone directed therapy with rituximab. Further treatment is pending.
Conclusion: Clinicians should be aware of MGRS. Collaboration with nephrology is key for proper diagnosis and prognosis. Consider treating more aggressively than MGUS to improve renal and hematologic outcomes. Prospective interventional studies are needed.
