This study aimed to 1) develop and test the reliability of a semiquantitative ultrasound score to assess muscle quality in patients with rheumatoid arthrit

Objectives: To assess the prognostic value of ultrasound-based quantification of vascular inflammation for predicting relapses in giant cell arteritis (GCA). Methods: The Monitoring Activity of GCA through UltraSound (MAGiCUS) project is an international, multicentre, prospective, observational study including newly diagnosed GCA patients. Ultrasound of temporal and axillary arteries was conducted at baseline, 1, 3, 6, and 12 months. Vascular inflammation was quantified using the OMERACT GCA Ultrasonographic Score (OGUS). The primary outcome was the occurrence of the first clinical relapse between 6 and 12 months. Results: Among 156 GCA patients from 19 centres, 31 (19.9%) experienced a relapse. In patients without a relapse, OGUS was significantly lower at all follow-up visits than baseline (-0.15 to -0.35). Baseline OGUS was significantly higher in relapsing patients (1.58 vs 1.16, p < 0.001). In multivariate analysis, an increase in 0.1 units in baseline OGUS was associated with relapse (OR 1.19, 95% CI 1.08, 1.34). This association remained significant for 0.1 increases in OGUS at 1 month (OR 1.37, 95% CI 1.17, 1.66) and at 3 months (OR 1.51, 95% CI 1.20, 1.98). The areas under the receiver operating characteristic curve for predicting relapse were 0.70 (95% CI 0.58 –0.80) for baseline OGUS, 0.74 (95% CI 0.60 –0.85) at 1 month, and 0.67 (95% CI 0.56 –0.78) at 3 months. Conclusion: Ultrasound-based quantification of vascular inflammation has prognostic value for predicting relapses during follow-up in GCA. Higher baseline, 1-month and 3-months OGUS are associated with an increased probability of clinical relapse.