OP0024 THE ROLE OF ULTRASONOGRAPHY IN EVALUATING IDIOPATHIC INFLAMMATORY MYOPATHIES: A STUDY INVESTIGATING THE ACCURACY OF B-MODE MUSCLE ULTRASOUND
Authors: C. Galluzzo, N. Pipitone, N. Possemato, F. Crescentini, B. Fautrel, Y. Allenbach, C. Salvarani, O. Benveniste
Journal: Annals of the Rheumatic Diseases (2024)

<h3>Background:</h3> Idiopathic inflammatory myopathies (IIM) represent a complex group of muscle diseases with diagnostic challenges. Muscle ultrasound (US) has recently gained attention for its potential in detecting muscle changes in IIM due to its non-invasive nature, accessibility, and cost-effectiveness. Previous studies have highlighted US as a promising tool for IIM evaluation, yet its diagnostic accuracy against the established gold standard of magnetic resonance imaging (MRI) warrants further exploration. This study seeks to assess the diagnostic utility of US in IIM. <h3>Objectives:</h3> The primary aim of this study was to assess the ability of US to identify alterations in selected muscles in patients with IIM and to evaluate its diagnostic accuracy. Ancillary objectives were to evaluate if there were differences in various parameters between patients with different US outcome, and to compare the performance of US with that of MRI. <h3>Methods:</h3> This prospective, cross-sectional, single-blind study enrolled patients with suspected or confirmed inflammatory myopathy at Pitié-Salpêtrière Hospital, Paris, from April to November 2023. Qualitative B-mode ultrasound assessments were conducted on 16 muscles bilaterally, evaluating echointensity and echotexture with recorded video clips. Outcomes were categorized as positive or negative based on qualitative assessment. Patient data, including demographics, anthropometrics, serum CK levels (U/L), and muscle strength (manual muscle testing (MMT) on Kendall's scale [0-10]), were recorded. Additionally, available MRI data collected from the patients were analyzed, with outcomes categorized as positive or negative based on signal intensity changes in T1-weighted or STIR sequences. <h3>Results:</h3> The study cohort consisted of 40 patients with myopathies, including 26 patients diagnosed with IIM (4 anti-synthetase syndrome, 5 dermatomyositis, 12 immune-mediated necrotizing myopathy, 5 overlap myositis), 8 patients with other myopathies (1 facioscapulohumeral muscular dystrophy, 1 vacuolar myopathy, 1 non specific myopathy, 1 dysferlinopathy, 4 inclusion-body myositis (IBM)) and 6 healthy subjects. Patients presenting with IBM were categorized in a separate group than non-IBM IIM category due to their distinct ultrasonographic features as evidenced by prior studies. All participants underwent US, and 31 of them had available MRI data. The median interval between US and MRI was 4 days (0-2482). Considering the clinical diagnosis made by the expert the diagnostic standard, in the IIM subgroup, US demonstrated a sensitivity of 84.6% and a specificity of 35.7%, with a positive predictive value (PPV) of 71.0% and a negative predictive value (NPV) of 55.6%. MRI showed a sensitivity of 68.4%, specificity of 41.7%, PPV of 65.0%, and NPV of 45.5%. Cohen's kappa coefficient indicated substantial agreement between US and MRI (Kappa = 0.620, 83% concordance, p = 0.004), including only patients for whom the interval between US and MRI was less than 30 days. Statistical analysis using Student's t-test revealed significant differences in disease duration and mean MMT scores between positive and negative results for both US and MRI. Binomial logistic regression indicated a significant association between disease duration and both US and MRI positivity. <h3>Conclusion:</h3> In this prospective, single-blind study qualitative muscle US demonstrated comparable diagnostic sensitivity to MRI. Both modalities had limited specificity for distinguishing IIM from other myopathies. Substantial agreement between US and MRI was observed, underscoring the potential of US as a valuable diagnostic tool. Disease duration emerged as a crucial parameter influencing positive US outcomes, emphasizing the need for its consideration in results' interpretation. Our study advocates a wider adoption of muscle US in the diagnostic setting of IIM. While recognizing MRI's unique strengths, the accessibility, cost-effectiveness, and diagnostic performance of US make it a promising tool. However, these results warrant further validation in larger, multi-center studies to confirm the reliability of US as a diagnostic tool for IIM. <h3>REFERENCES:</h3> <b>NIL.</b> <h3>Acknowledgements:</h3> Claudio Galluzzo wishes to express profound appreciation for the grant support provided by the European League Against Rheumatism (EULAR). This EULAR long-term grant has been essential in supporting the research activities related to this publication. <h3>Disclosure of Interests:</h3> <b>None declared.</b>