OP0248 MAGNETIC RESONANCE IMAGING OF SHOULDER GIRDLE IN POLYMYALGIA RHEUMATICA – INFLAMMATORY FINDINGS AND THEIR DIAGNOSTIC VALUE
Authors: M. Fruth, L. Künitz, P. Martin-Seidel, S. Tsiami, X. Baraliakos
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Non-synovial inflammation as detected by magnetic resonance imaging (MRI) and FDG-PET/CT have recently been described as characteristic imaging features in polymyalgia rheumatica (PMR). While the diagnostic ability of FDG-PET/CT in PMR has been demonstrated in recent studies, the value of MRI is undefined. <h3>Objectives:</h3> To describe inflammatory MRI findings in shoulder girdle of patients with PMR and evaluate their discriminatory potential against other causes of shoulder girdle pain. <h3>Methods:</h3> Retrospective study of 496 contrast-enhanced MRI scans of the shoulder girdle from 122 PMR patients and 374 non-PMR cases. Two radiologists blinded to clinical and demographic information evaluated inflammation at 6 non-synovial sites (Figure 1) and 3 synovial sites for presence or absence of inflammation. Non-synovial sites: around axillary recess of fibrous humeroglenoidal capsule (CAP), around tendinous origin of long head triceps brachii (LHT), around coracoclavicular ligament (CC), around intramuscular tendon of subscapularis muscle (SSC), around intramuscular tendon of infraspinatus muscle (IS) and around tendinous origins of short head biceps brachii and coracobrachialis muscle (BBSH) at the tip of coracoid process. Synovial sites: subacromial bursa (SAB), humeroglenoidal joint (HGJ) and tendon sheath of long head biceps brachii (LBTS). Prevalence of synovial and non-synovial inflammation were analysed and tested alone, in combination and together with clinical information for their ability to differentiate PMR from non-PMR. <h3>Results:</h3> High prevalence of non-synovial inflammation was identified as prominent imaging finding in PMR, in average 3.4±1.7 out of the 6 predefined non-synovial sites were inflamed compared to 1.1±1.4 in non-PMR group, p&lt;0.001. The detection of inflammation at 3 out of 6 predefined non-synovial sites differentiated PMR patients from controls with a sensitivity/specificity of 73.8%/85.8%, respectively (area under the curve (auc) 0.840, Figure 2). A lower diagnostic threshold of at least 2 inflamed non-synovial sites still performed excellent, with a sensitivity increased to 84.4% at the expense of a lowered specificity of 73.8%. Presence of synovitis also differed significantly between PMR patients and non-PMR cases, 2.5±0.8 versus 1.9±1.1 out of 3 predefined synovial sites (p&lt;0.001). The optimal threshold for synovitis detection was at least 2 inflamed synovial sites to differentiate PMR from non-PMR cases, but performed only moderately, sensitivity/specificity of 86.1%/36.1%, respectively (auc 0.649). The discriminatory potential of synovitis detection markedly improved if concomitant elevated inflammatory markers and bilateral shoulder girdle pain were present (auc 0.755). This combination of clinical and imaging features improved especially the specificity to 73.5% while sensitivity decreased to 72.1% when synovitis was present at least at 2 synovial sites. The discriminatory potential of prevalence of non-synovial inflammation in concomitant presence of synovial inflammation at SAB or LBTS performed only slightly inferior compared to sole prevalence of non-synovial inflammation (auc 0.837). Detection of at least 2 inflamed non-synovial sites in presence of synovitis of SAB or LBTS differentiated PMR from non-PMR with a sensitivity/specificity of 83.6%/74.6%, improving specificity slightly at the cost of sensitivity compared to sole prevalence of non-synovial inflammation. <h3>Conclusion:</h3> Contrast-enhanced MRI of the shoulder girdle is a reliable imaging tool with significant diagnostic value in assessment of patients suffering from PMR. It has a convincing discriminatory effect to differentiate from other causes of shoulder girdle pain and therefore help diagnostic decision-making in equivocal cases. <h3>REFERENCES:</h3> <b>NIL.</b> <h3>Acknowledgements:</h3> <b>NIL.</b> <h3>Disclosure of Interests:</h3> <b>None declared.</b>