{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,27]],"date-time":"2026-03-27T12:12:16Z","timestamp":1774613536565,"version":"3.50.1"},"reference-count":39,"publisher":"MDPI AG","issue":"7","license":[{"start":{"date-parts":[[2026,3,27]],"date-time":"2026-03-27T00:00:00Z","timestamp":1774569600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["JCM"],"abstract":"<jats:p>Background: Rapidly progressive glomerulonephritis (RPGN) is a severe nephrological emergency, frequently secondary to anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis. In older adults, the coexistence of comorbidities and monoclonal gammopathy of undetermined significance (MGUS) makes it difficult to distinguish between ANCA vasculitis and monoclonal gammopathy of renal significance (MGRS), which differ in prognosis and treatment. The coexistence of PR3-ANCA-associated vasculitis and MGUS is uncommon and sparsely documented. Case Presentation: A 72-year-old woman with hypertension and type 2 diabetes presented with acute deterioration and rapidly progressive renal failure, requiring hemodialysis. She had subnephrotic proteinuria, hematuria, and an active urinary sediment. The autoimmune workup showed ANCA negativity using immunofluorescence, but PR3-ANCA positivity using ELISA. Hematologic characterization documented an IgG kappa monoclonal spike; no bone lesions, amyloidosis, or criteria for multiple myeloma were found; and the patient was classified as MGUS. Renal biopsy revealed necrotizing extracapillary pauci-immune glomerulonephritis with cellular and fibrocellular crescents and no monoclonal deposits, consistent with PR3-ANCA vasculitis. Induction therapy with methylprednisolone pulses and oral prednisone was initiated; cyclophosphamide was not administered because of catheter-associated Staphylococcus aureus bacteremia and upper gastrointestinal bleeding complicated by disseminated intravascular coagulation. The patient died on day 25 due to infectious and hemorrhagic complications. Conclusions: This case provides additional documentation of an uncommon overlap between PR3-ANCA-associated vasculitis and MGUS in a Latin American patient and highlights the role of renal biopsy in distinguishing MGRS from pauci-immune vasculitis in the presence of paraproteinemia. It also underscores the need to tailor immunosuppression in frail older adults, balancing disease control against the risk of severe infection.<\/jats:p>","DOI":"10.3390\/jcm15072554","type":"journal-article","created":{"date-parts":[[2026,3,27]],"date-time":"2026-03-27T11:12:25Z","timestamp":1774609945000},"page":"2554","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":0,"title":["PR3-ANCA-Associated Vasculitis in IgG\u03ba MGUS: A Fatal Case of Rapidly Progressive Glomerulonephritis"],"prefix":"10.3390","volume":"15","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-8629-8527","authenticated-orcid":false,"given":"Carlos","family":"Berrocal","sequence":"first","affiliation":[{"name":"Departamento de Medicina Interna, Universidad del Valle, Cali 760032, Colombia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9167-9204","authenticated-orcid":false,"given":"\u00c1lvaro","family":"Arbel\u00e1ez-Cort\u00e9s","sequence":"additional","affiliation":[{"name":"Departamento de Medicina Interna, Universidad del Valle, Cali 760032, Colombia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7636-7149","authenticated-orcid":false,"given":"Alyi","family":"Arellano","sequence":"additional","affiliation":[{"name":"Departamento de Medicina Interna, Universidad del Valle, Cali 760032, Colombia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Antonio","family":"Pe\u00f1a","sequence":"additional","affiliation":[{"name":"Departamento de Medicina Interna, Universidad del Valle, Cali 760032, Colombia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-1890-4983","authenticated-orcid":false,"given":"H. A.","family":"Nati-Castillo","sequence":"additional","affiliation":[{"name":"Programa de Medicina, Facultad de Salud, Universidad Santiago de Cali, Cali 760045, Colombia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Nancy","family":"Mejia","sequence":"additional","affiliation":[{"name":"Departamento de Medicina Interna, Universidad del Valle, Cali 760032, Colombia"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-2760-8791","authenticated-orcid":false,"given":"Alice","family":"Gaibor-Pazmi\u00f1o","sequence":"additional","affiliation":[{"name":"One Health Research Group, Universidad de Las Am\u00e9ricas, Quito 170125, Ecuador"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0009-0002-3717-383X","authenticated-orcid":false,"given":"Marlon","family":"Arias-Intriago","sequence":"additional","affiliation":[{"name":"Pathology Department, SOLCA (Sociedad de Lucha Contra el C\u00e1ncer del Ecuador), Quito 170138, Ecuador"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1178-0546","authenticated-orcid":false,"given":"Juan S.","family":"Izquierdo-Condoy","sequence":"additional","affiliation":[{"name":"One Health Research Group, Universidad de Las Am\u00e9ricas, Quito 170125, Ecuador"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2026,3,27]]},"reference":[{"key":"ref_1","unstructured":"Rout, P., and Leslie, S.W. 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