{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,11,28]],"date-time":"2025-11-28T15:30:03Z","timestamp":1764343803417,"version":"3.46.0"},"reference-count":16,"publisher":"Oxford University Press (OUP)","issue":"2","license":[{"start":{"date-parts":[[2025,1,1]],"date-time":"2025-01-01T00:00:00Z","timestamp":1735689600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/academic.oup.com\/pages\/standard-publication-reuse-rights"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":[],"published-print":{"date-parts":[[2025,7,25]]},"abstract":"<jats:title>Abstract<\/jats:title>\n                  <jats:p>Microscopic polyangiitis (MPA), a form of ANCA-associated vasculitis (AAV), can present a diagnostic challenge when it manifests with atypical symptoms. We report a case of MPA where the predominant clinical feature was myalgia with normal creatine kinase levels, underscoring the importance of a comprehensive diagnostic approach. A 60-year-old male presented with bilateral lower leg myalgia and gait disturbance. Physical examination revealed muscle tenderness and weakness. Magnetic resonance imaging (MRI) with fat-suppressed T2-weighted imaging showed heterogeneous high signal intensity in the lower limb muscles, suggestive of myositis. However, laboratory investigations found normal serum creatine kinase levels, and all tested myositis-specific autoantibodies were negative. A muscle biopsy yielded inconclusive results. In contrast, serology was positive for myeloperoxidase\u2013antineutrophil cytoplasmic antibody (MPO-ANCA). Despite preserved kidney function and unremarkable urinalysis, a kidney biopsy was performed, which revealed fibrinoid necrosis in small arteries. This led to a definitive diagnosis of MPA. This case highlights that MPA should be considered a key differential diagnosis in patients presenting with myalgia, particularly in the presence of a positive MPO-ANCA serology. While muscle manifestations occur in ~20% of AAV cases, they are not included in the current classification criteria. Our findings underscore that kidney biopsy remains a critical diagnostic tool for establishing a definitive diagnosis of MPA, even when renal symptoms are minimal, facilitating timely and appropriate immunosuppressive therapy.<\/jats:p>","DOI":"10.1093\/mrcr\/rxaf062","type":"journal-article","created":{"date-parts":[[2025,11,7]],"date-time":"2025-11-07T13:04:36Z","timestamp":1762520676000},"source":"Crossref","is-referenced-by-count":0,"title":["Myalgia as initial presentation of microscopic polyangiitis: diagnostic utility of kidney biopsy"],"prefix":"10.1093","volume":"9","author":[{"ORCID":"https:\/\/orcid.org\/0009-0004-8639-6911","authenticated-orcid":false,"given":"Miyu","family":"Wakatsuki","sequence":"first","affiliation":[{"name":"Nephrology Center and Department of Rheumatology, Toranomon Hospital Kajigaya , Kanagawa ,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Yuki","family":"Oba","sequence":"additional","affiliation":[{"name":"Nephrology Center and Department of Rheumatology, Toranomon Hospital Kajigaya , Kanagawa ,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Junko","family":"Kanda-Kikuchi","sequence":"additional","affiliation":[{"name":"Department of Neurology, Toranomon Hospital Kajigaya , Kanagawa ,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kei","family":"Kono","sequence":"additional","affiliation":[{"name":"Department of Pathology, Toranomon Hospital , Tokyo ,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Masayuki","family":"Yamanouchi","sequence":"additional","affiliation":[{"name":"Nephrology Center and Department of Rheumatology, Toranomon Hospital Kajigaya , Kanagawa 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Science of Tokyo , Tokyo ,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Naoki","family":"Sawa","sequence":"additional","affiliation":[{"name":"Nephrology Center and Department of Rheumatology, Toranomon Hospital Kajigaya , Kanagawa ,","place":["Japan"]}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"286","published-online":{"date-parts":[[2025,11,8]]},"reference":[{"key":"2025112810272805400_ref1","doi-asserted-by":"crossref","first-page":"71","DOI":"10.1038\/s41572-020-0204-y","article-title":"ANCA-associated vasculitis","volume":"6","author":"Kitching","year":"2020","journal-title":"Nat Rev Dis Primers"},{"key":"2025112810272805400_ref2","doi-asserted-by":"crossref","first-page":"321","DOI":"10.1136\/annrheumdis-2021-221796","article-title":"2022 American College of Rheumatology\/European Alliance of Associations for Rheumatology classification criteria for microscopic 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