• Hyeonjeong Lee, Jaeseok Yang, Jinykung Kwon, Mihwa Heo, Yaerim Kim, Jin Hyuk Paek, Hyeongchan Shin, Misun Choe, Seungyeup Han, and Kyubok Jin.
• Division of Nephrology, Department of Internal Medicine, Keimyung University School of Medicine, Keimyung University Kidney Institute, Daegu, Republic of Korea.
• Medicine (Baltimore). 2024 Jul 26; 103 (30): e39021e39021.

RationaleImmune-mediated vasculitis with 2 or more autoantibodies, for example, anti-proteinase-3, combined with anti-myeloperoxidase (MPO) or anti-glomerular basement membrane (GBM) antibodies, is extremely unusual. Furthermore, the coexistence of autoimmune vasculitis and hematological malignancies is uncommon. Herein, we describe a case of double-seropositive anti-neutrophil cytoplasmic antibody (ANCA) vasculitis with multiple myeloma.Patient ConcernsA 79-year-old Asian man presented with persistent leg edema and kidney dysfunction. His kidney function rapidly decreased, and serologic test results showed higher titers of the anti-MPO antibody (54.7 IU/mL) and anti-GBM antibodies (>200 IU/mL). Additionally, the clinical features showed the possibility of monoclonal gammopathy with anemia and hyperglobulinemia. We performed kidney and bone marrow biopsy. Serum protein electrophoresis and immunofixation revealed no significant differences, but the results of the bone marrow smear were compatible with those of myeloma with 15% plasmacytosis. However, kidney biopsy showed diffuse crescentic glomerulonephritis without deposition of the immune complex or kappa/lambda chain.Diagnoses And InterventionsFinally, the patient was diagnosed with double-seropositive ANCA-associated glomerulonephritis and multiple myeloma. Given the patient's performance status, we initiated low-dose steroid pulse therapy, followed by conservative management.OutcomesWhile the pulmonary lesions showed improvement, the kidney function did not regain its previous state, prompting the initiation of kidney replacement therapy by hemodialysis. There has been a decrease in the levels of anti-GBM and anti-MPO antibodies since the initial diagnosis.LessonsThis case elucidates the complex interplay between ANCA-associated glomerulonephritis and hematologic malignancy and emphasizes the need for a nuanced treatment strategy considering its multifaceted clinical presentation.Copyright © 2024 the Author(s). Published by Wolters Kluwer Health, Inc.

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