This was a retrospective cross-sectional study including patients referred to a US fast track clinic (FTC) [2] at our Academic Center for screening of possible GCA over a 2-year period (from June 2019 to June 2021). Patients with suspected GCA are referred to this US clinic for examination within 24 h per protocol. For the purposes of this study, only consecutive patients with GCA suspicion were included. The study was performed in routine clinical practice conditions.

The following variables were collected from the electronic health records: demographics, presenting symptoms (headache, scalp tenderness, jaw claudication, visual symptoms and ocular ischemia diagnosis by an ophthalmologist, fever, polymyalgia rheumatica, and constitutional symptoms), previous use of glucocorticoids, and laboratory variables as C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), hemoglobin, and platelets. TA biopsy data were also included if available. The gold standard for GCA diagnosis was the clinical confirmation by the treating clinician after a 6 months follow-up. The clinical GCA diagnosis could be dismissed according to the clinician criteria, even in patients fulfilling ACR 1990 criteria or with positive imaging tests, if another more reasonable diagnosis was established.

To assess the CVR, the following variables were collected: body weight, height and body mass index, history of acute myocardial infarction, acute coronary syndromes, transient ischemic attack, stroke, aortic aneurism, peripheral artery disease, diabetes mellitus with or without organ damage, estimated glomerular filtration rate (eGFR) using the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) formula, cholesterol level (total cholesterol, high-density lipoprotein cholesterol and low-density lipoprotein cholesterol), systolic and diastolic blood pressure, and smoking habit (current or previous smoker). The European Society of Cardiology (ESC) Guidelines on CV Disease Prevention in clinical practice were applied to define four different categories of CVR [18]. We calculated the risk score of each patient using the available ESC CVD Risk Calculator app for mobile devices (https://www.escardio.org/Education/ESC-Prevention-of-CVD-Programme/Risk-assessment/esc-cvd-risk-calculation-app), and subjects were classified as very high, high, moderate, or low CVR. Patients with high or very high CVR were compared with patients with low or moderate CVR to determine differences in the diagnostic accuracy of the Halo Score.

The three TA segments (common superficial TA, its parietal and frontal branches) and extracranial (carotid, subclavian and distal axillary) arteries were bilaterally evaluated by US in all patients within 24 h per protocol (excluding weekends with delays up to 48 h). The exam was performed in a supine position, by a single experienced ultrasonographer (JMC) using an EsaoteMyLab8 (Esaote, Genoa) with a hockey stick 12–18 MHz high frequency transducer for the temporal arteries and an 8–14 frequency transducer for extracranial arteries. The distal axillary arteries were scanned from the axillary fossa. The focus was positioned at 5 mm below the skin for the TA and 2–3 cm for the axillary arteries. The pulse repetition frequency was 2–3 kHz. The color box was set at an angle between sound waves and artery < 60°. The presence or absence of a halo, compression, stenosis, or occlusion for cranial arteries and the presence of a halo for extracranial arteries were evaluated. The IMT was measured in gray scale mode in all the arteries included in the protocol if technically possible due to the maximum frequency probe (18 MHz). Doppler color mode was only used to better delineate the lumen of the vessel to improve the visibility of the IMT in unclear cases. The extent of vascular inflammation was quantified according to the Halo Score, identifying the maximum IMT in each artery and calculating the composite score according to predefined cut-off values. The halo grade scores of the axillary arteries were multiplied by a factor of 3. The Halo score values could range from 0 to 48 [10]. The presence of a halo and/or compression sign in temporal arteries or the presence of a halo in extracranial arteries in the absence of atherosclerosis was considered sufficient for a positive US examination. The ultrasonographer was not blinded to the clinical information of the patient.

Quantitative data were described as mean (standard deviation, SD) and qualitative variables as absolute frequency (percentages). Chi-square test or Fisher’s exact test were used to analyze differences between proportions; Student’s t test was used for comparison between means. Criterion validity was evaluated using receiver operating characteristic (ROC) curves with GCA clinical diagnosis as external criterion and construct validity was determined by Spearman’s rank correlation coefficient (rho). All tests were two-sided; p values < 0.05 were considered statistically significant. The SPSS software (version 23.0; IBM, USA) was used for statistical analysis.

This study was performed in accordance with the ethical standards of the responsible committee on human experimentation and the Helsinki Declaration of 1975, as revised in 1983. Research ethics committee approval for the protocol was obtained prior to commencing the study (RHEUM0322). The committee determined that written informed consent was not mandatory.