Giant Cell Arteritis (GCA): An international, multicentre, longitudinal evaluation of clinical, laboratory and ultrasound parameters in the diagnosis, prognosis and monitoring of GCA.

Background: Giant cell arteritis (GCA) is a vasculitis, varies in extent, severity and outcomes, hence requires disease stratification for targeted management. Ultrasound (US) non-compressible halo is currently categorised in a dichotomous pattern. We developed a US scoring system to quantify the extent of vascular inflammation and investigated its diagnostic accuracy and association with clinical factors in GCA. Methods: HAS GCA is a prospective study recruited from 7 European GCA fast-track clinics. Southend probability score (GCAPS) risk-stratified patients into 3 categories. Temporal and axillary US Halo Scores (HS) were calculated from the halo thickness and extent in bilateral temporal arteries, parietal and frontal branches (TAHS) and axillary arteries (AAHS). These scores were summed to generate a Total Halo Score (THS). GCA patients had US at baseline,1,3,6,12 months. Primary outcome was remission at 12 months (prednisolone ≤ 5mg). Results: 229 participants (84 GCA) were included: 73 completed follow-ups, 11 lost to follow-up and 65 achieved remissions (figure). GCA median age was 75 years. GCAPS stratified GCA and controls to Low risk (0% vs 46%; Sn-undefined, Sp-99), Intermediate risk (21% vs 38%; Sn-83, Sp-98) and High risk (79% vs 16%; Sn-99, Sp-91). The optimal GCAPS cut-off point was ≥12 (Sn-89, Sp-78). Median THS was 21.5 in GCA and 8 in controls. Optimal cut-off Halo Score in diagnosis was TAHS ≥6 (Sn-86, Sp-92), AAHS ≥11 (Sn-52, Sp-75), THS ≥17 (Sn-76%, Sp-91%). At 12 months, median TAHS, AAHS and THS reduced from 13 to 3, 12 to 9 and 21.5 to 12, respectively. Conclusion: Along with GCAPS, Halo Score successfully discriminates GCA from non-GCA. Extent of arterial inflammation in GCA can be quantified by ultrasound halo scoring.