Polyarteritis Nodosa and Sarcoidosis Presenting with Myalgia and Myositis-Mimicking MRI Findings: A Report of Two Cases.

Authors

Masayuki Shinojima, Satoshi Kubo, Ippei Miyagawa, Yasuyuki Todoroki, Masatsune Ueno, Yoshiya Tanaka, Shingo Nakayamada

Published in

Modern rheumatology case reports. Jul 10, 2026. Epub Jul 10, 2026.

Abstract

Diseases presenting with muscle symptoms are diverse. We report two cases initially suspected of idiopathic inflammatory myopathies (IIMs) that were ultimately diagnosed as polyarteritis nodosa and sarcoidosis, respectively. Case 1 was a 30-year-old man with fever, limb muscle pain, and elevated inflammatory markers. Muscle MRI showed high signal intensity on fat-suppressed T2-weighted images, and biopsy revealed vasculitis with fibrinoid necrosis, leading to a diagnosis of polyarteritis nodosa. Case 2 was a 70-year-old man with proximal muscle pain and weakness and elevated muscle enzymes. MRI showed high signal intensity in the thigh muscles, and biopsy revealed noncaseating granulomas consistent with sarcoidosis. These cases highlight the diagnostic pitfalls of interpreting MRI findings and serum creatine kinase levels in isolation when evaluating suspected IIMs and underscore the critical role of histopathological evaluation, including muscle biopsy, in establishing an accurate diagnosis.

PMID:
42430520
Bibliographic data and abstract were imported from PubMed on 11 Jul 2026.

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