Lymphoplasmacytic Lymphoma with Extensive Subendothelial Deposits Resembling Wire Loop Lesions: A Case Report

Introduction: Lymphoplasmacytic lymphoma (LPL) is an indolent B-cell non-Hodgkin lymphoma that primarily involves lymphocytes differentiating into plasma cells producing IgM-type immunoglobulins. It can occasionally present with renal impairment. Here, we report a rare case of LPL with renal lesions resembling wire loop lesions of lupus nephritis. Case Description: A 65-year-old male presented with leg edema and proteinuria. A renal biopsy revealed numerous glomeruli with wire loop-like lesions (Left Figure). IF staining showed deposits of IgG, IgA, IgM, C3, and C1q in the mesangial and subendothelial regions, with positive κ light chain. Congo-red staining was negative. Electron microscopy identified extensive subendothelial deposits (Right Figure). Tests for antinuclear and anti-DNA antibodies were negative, with no extrarenal manifestations of systemic lupus erythematosus. Immunoelectrophoresis detected an IgM-κ type M protein in the serum, and cryoglobulins were negative. A bone marrow biopsy confirmed LPL. Upon presentation, the laboratory results were as follows: serum creatinine (S-Cr) 1.49 mg/dL, urine protein/creatinine ratio 1.54 g/gCr, and CH50 <14.0 U/mL. The patient was started on DRC therapy (dexamethasone, rituximab, and cyclophosphamide), resulting in a decreasing trend in IgM to 128 mg/dL, proteinuria to 0.37 g/gCr, and S-Cr to 1.41 mg/dL at 6 months. Discussion: Renal complications of LPL include hyperviscosity syndrome, amyloidosis, and cryoglobulinemia. This case featured widespread subendothelial deposits, resembling lupus nephritis wire loop lesions. To our knowledge, such lesions have not been previously reported in LPL. Chemotherapy led to reductions in IgM levels, proteinuria, and improved renal function, indicating monoclonal IgM’s role in forming these lesions.