{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,7,8]],"date-time":"2026-07-08T14:20:46Z","timestamp":1783520446678,"version":"3.55.0"},"reference-count":12,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2026,7,8]],"date-time":"2026-07-08T00:00:00Z","timestamp":1783468800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Med."],"abstract":"<jats:sec>\n                    <jats:title>Background<\/jats:title>\n                    <jats:p>Distinguishing immune complex-mediated membranoproliferative glomerulonephritis (IC-MPGN) with coincident monoclonal gammopathy of undetermined significance (MGUS) from monoclonal gammopathy of renal significance (MGRS) remains challenging when biopsy sampling is inadequate and gold-standard pathologic workup is incomplete.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Case Presentation<\/jats:title>\n                    <jats:p>A 60-year-old woman presented with upper abdominal fullness and heartburn. Routine testing revealed nephrotic-range proteinuria, acute kidney injury (AKI), and hypocomplementemia. Serum immunofixation showed IgM-\u03ba monoclonal gammopathy. Bone marrow examination identified a clonal B-lymphocyte population of approximately 1% with no evidence of lymphoplasmacytic lymphoma or multiple myeloma. Kidney biopsy demonstrated IC-MPGN type I with mesangial and subendothelial electron-dense deposits. Immunofluorescence revealed granular deposition of IgG, IgM, C3, kappa, and lambda, indicating a polyclonal immune complex pattern. Cryoglobulin testing was negative on three occasions under strict 37 \u00b0C conditions. These findings suggested but could not confirm IC-MPGN with coincident IgM-\u03ba MGUS; MGRS could not be excluded because only one non-sclerotic glomerulus was available for light microscopy and pronase-digested paraffin immunofluorescence was not performed. The patient received methylprednisolone pulse therapy followed by rituximab. At 1-month follow-up, serum albumin increased from 25.6 to 31.3 g\/L, serum creatinine decreased from a peak of 231.0 to 94.0 \u03bcmol\/L, and 24-h urine protein decreased from 7,930 mg to 1.1 g. Complement C3 and C4 normalized. Clinical improvement was observed following combined therapy; however, the independent contribution of rituximab cannot be determined from this single case.<\/jats:p>\n                  <\/jats:sec>\n                  <jats:sec>\n                    <jats:title>Conclusion<\/jats:title>\n                    <jats:p>This case underscores the diagnostic uncertainty inherent in distinguishing coincident MGUS from MGRS when polyclonal immunofluorescence coexists with monoclonal gammopathy but gold-standard pathologic workup is incomplete. It highlights the need for standardized pathologic evaluation, including pronase-digested paraffin immunofluorescence, and illustrates that routine urinalysis in older adults with non-renal symptoms can reveal clinically significant kidney disease.<\/jats:p>\n                  <\/jats:sec>","DOI":"10.3389\/fmed.2026.1869336","type":"journal-article","created":{"date-parts":[[2026,7,8]],"date-time":"2026-07-08T13:47:57Z","timestamp":1783518477000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":0,"title":["Case Report: Diagnostic uncertainty in IC-MPGN coexisting with IgM-\u03ba MGUS"],"prefix":"10.3389","volume":"13","author":[{"given":"Qishun","family":"Wu","sequence":"first","affiliation":[{"name":"Department of Nephrology, The Second Affiliated Hospital of Wannan Medical University","place":["Wuhu, Anhui, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ling","family":"Yang","sequence":"additional","affiliation":[{"name":"Department of Nephrology, The Second Affiliated Hospital of Wannan Medical University","place":["Wuhu, Anhui, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Xin","family":"Lin","sequence":"additional","affiliation":[{"name":"Department of Nephrology, The Second Affiliated Hospital of Wannan Medical University","place":["Wuhu, Anhui, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhiliang","family":"Yu","sequence":"additional","affiliation":[{"name":"Department of Nephrology, The Second Affiliated Hospital of Wannan Medical University","place":["Wuhu, Anhui, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Zhangli","family":"Wu","sequence":"additional","affiliation":[{"name":"Department of Nephrology, The Second Affiliated Hospital of Wannan Medical University","place":["Wuhu, Anhui, China"]}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"1965","published-online":{"date-parts":[[2026,7,8]]},"reference":[{"key":"B1","doi-asserted-by":"publisher","first-page":"712","DOI":"10.3390\/cells12050712","article-title":"Diagnostic and prognostic comparison of immune-complex-mediated membranoproliferative glomerulonephritis and C3 glomerulopathy","volume":"12","author":"Kovala","year":"2023","journal-title":"Cells."},{"key":"B2","doi-asserted-by":"publisher","first-page":"2003","DOI":"10.1007\/s12325-025-03167-x","article-title":"Expert discussion on immune complex-mediated membranoproliferative glomerulonephritis: challenges and considerations","volume":"42","author":"Lafayette","year":"2025","journal-title":"Adv Ther."},{"key":"B3","doi-asserted-by":"publisher","first-page":"45","DOI":"10.1038\/s41581-018-0077-4","article-title":"The evaluation of monoclonal gammopathy of renal significance: a consensus report of the International Kidney and Monoclonal Gammopathy Research Group","volume":"15","author":"Leung","year":"2019","journal-title":"Nat Rev Nephrol."},{"key":"B4","first-page":"227","article-title":"The complexity and conundrums of monoclonal gammopathy of renal significance: MGRS vs non-MGRS","volume":"100","author":"Sethi","year":"2021","journal-title":"Kidney Int."},{"key":"B5","doi-asserted-by":"publisher","first-page":"7","DOI":"10.1093\/ndt\/gfz176","article-title":"Proliferative glomerulonephritis with monoclonal immunoglobulin deposits: a new entity","volume":"6","author":"Nasr","year":"2011","journal-title":"Clin J Am Soc Nephrol."},{"key":"B6","doi-asserted-by":"publisher","first-page":"506","DOI":"10.1053\/j.ajkd.2013.02.370","article-title":"C3 glomerulonephritis associated with monoclonal gammopathy: a case series","volume":"62","author":"Zand","year":"2013","journal-title":"Am J Kidney Dis."},{"key":"B7","doi-asserted-by":"publisher","first-page":"611","DOI":"10.1007\/s40620-020-00723-2","article-title":"Clone-directed therapy for proliferative glomerulonephritis with monoclonal immunoglobulin depositions: is it always necessary? 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