POS0553 Muscle MRI in polyarteritis nodosa: consistent findings in 6 patients

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Background: The gold standard for diagnosing polyarteritis nodosa (PAN) remains histopathological work-up. However, imaging techniques such as conventional angiography and abdominal CT/MR angiography are increasingly been used for detecting medium vessel involvement. Recent advances in imaging technology have made muscle MRI a promising tool for investigating vasculitis-related changes in extremity muscles. Objectives: We aimed in this study to describe muscle MRI findings in a prospective cohort of PAN patients. Methods: The Registry of HUVAC (Hacettepe University Vasculitis Research Centre) was established in 2014. From its inception onwards, all newly diagnosed/routine follow-up patients were prospectively registered in the database. From this registry, data on demographic characteristics, clinical presentation, underlying disease, muscle biopsy results, and MRI findings of PAN patients presenting with muscle involvement were collected and reviewed. Results: Of the 72 PAN patients in the registry including secondary PAN (hepatitis B-related, familial Mediterranean fever (FMF)-associated, adenosine deaminase 2 deficiency) 6 had muscle MRI because of severe myalgia and increased acute phase reactants (APRs) in the initial differential diagnosis period. Muscle enzyme elevation was inconsistent. FMF was the most common underlying disease and in 1 patient there was additional latent hepatitis B infection (Table 1). Muscle MRI consistently showed focal or patchy myositis with central tortuous and/or dilated vessels, most often affecting the quadriceps femoris, hamstring, and gastrocnemius muscles (Figure 1). Microaneurysmal dilatations and perifascial edema were commonly noted, consistent with PAN-associated muscle vasculitis. Muscle biopsy in one of the cases confirmed vasculopathic changes and myopathic features. Conclusion: Muscle MRI demonstrates characteristic findings suggestive of PAN, such as focal myositis with central vascular abnormalities and perifascial edema, making it a valuable non-invasive diagnostic tool. Consistent imaging patterns supporting PAN diagnosis may defer or even obviate biopsy in selected patients especially with elevated APRs and myalgia/leg pain. Table 1. Demographic, clinical and MRI features of patients . Figure 1Fat-saturated (FS) T1-weighted (T1W) pre- ( a ) and post-contrast ( b ), and T2W FS ( c ) axial MR images through the right calf in a 43-year-old male show active intramuscular vasculitis (arrows, b ) surrounded by muscle edema ( c ). Muscle biopsy revealed vasculopathic changes and myopathic features. REFERENCES: NIL . Acknowledgements: NIL . Disclosure of Interests: Omer Karadag: None declared, Büşra Firlatan Yazgan: None declared, Gizem Ayan: None declared, Ertugrul Cagri Bolek: None declared, Umut Kalyoncu: None declared, Adalet Elcin Yildiz: None declared, Ustun Aydingoz has received speaker fees from GE Healthcare, and consultancy fees from GE Healthcare. © The Authors 2025. This abstract is an open access article published in Annals of Rheumatic Diseases under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Neither EULAR nor the publisher make any representation as to the accuracy of the content. The authors are solely responsible for the content in their abstract including accuracy of the facts, statements, results, conclusion, citing resources etc.