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Routine immunofluorescence (IF) on frozen tissue failed to demonstrate immunoglobulin deposits; however, IF performed on formalin-fixed paraffin-embedded tissue following pronase digestion revealed masked monotypic lambda light chain deposits. This case highlights the diagnostic challenge posed by masked deposits and underscores the importance of advanced IF techniques in complex cases of cryoglobulinaemia.<\/jats:p>","DOI":"10.1136\/bcr-2025-269981","type":"journal-article","created":{"date-parts":[[2026,5,28]],"date-time":"2026-05-28T12:30:19Z","timestamp":1779971419000},"page":"e269981","update-policy":"https:\/\/doi.org\/10.1136\/crossmarkpolicy","source":"Crossref","is-referenced-by-count":0,"title":["Severe cryoglobulinaemic vasculitis associated with monoclonal gammopathy: a diagnostic challenge of masked deposits"],"prefix":"10.1136","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0009-0005-1384-8195","authenticated-orcid":false,"given":"Beatriz Pedro","family":"Fernandes","sequence":"first","affiliation":[{"name":"Nephrology, ULS Coimbra, Coimbra, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Alexandra","family":"Esteves","sequence":"additional","affiliation":[{"name":"Nephrology, ULS Coimbra, Coimbra, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Ana Carolina","family":"Pimenta","sequence":"additional","affiliation":[{"name":"Nephrology, ULS Coimbra, Coimbra, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Lu\u00eds","family":"Rodrigues","sequence":"additional","affiliation":[{"name":"Nephrology, Centro Hospitalar e Universit\u00e1rio de Coimbra, Coimbra, Portugal, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Nuno","family":"Oliveira","sequence":"additional","affiliation":[{"name":"Nephrology, centro Hospitalar e Universit\u00e1rio de Coimbra, Coimbra, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"V\u00edtor","family":"Sousa","sequence":"additional","affiliation":[{"name":"Coimbra\u2019s Medical College, Coimbra, USA"},{"name":"Coimbra\u2019s Hospital and Universitary Center, Coimbra, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]},{"given":"Rui","family":"Alves","sequence":"additional","affiliation":[{"name":"Nephrology, centro Hospitalar e Universit\u00e1rio de Coimbra, Coimbra, Portugal"},{"name":"Universidade de Coimbra Faculdade de Medicina, Coimbra, Coimbra, Portugal"}],"role":[{"vocabulary":"crossref","role":"author"}]}],"member":"239","published-online":{"date-parts":[[2026,5,27]]},"reference":[{"key":"2026090305052684000_19.5.e269981.1","doi-asserted-by":"publisher","DOI":"10.1182\/blood-2012-07-445304"},{"key":"2026090305052684000_19.5.e269981.2","doi-asserted-by":"publisher","DOI":"10.1681\/ASN.2017121319"},{"key":"2026090305052684000_19.5.e269981.3","doi-asserted-by":"publisher","DOI":"10.1038\/s41581-018-0077-4"},{"key":"2026090305052684000_19.5.e269981.4","unstructured":"Johnson RJ , Feehally J , Floege J , et al . 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