## 4 Discussion  
Over the last decade, the growing evidence supporting the use of US has led to a radical revolution in the management of patients with GCA [13]. According to the 2018 update of the EULAR recommendations for the management of LVV, a diagnosis of GCA should be confirmed by either imaging techniques or histologic examination in order to increase the diagnostic accuracy [14,15]. In specialized centers provided with the adequate machine equipment and appropriate expertise, TA and AX US has become the first-line imaging modality in case of suspected GCA. In recent years, the application of US as part of FTA clinics has progressively reduced the need for TAB in patients presenting with signs and symptoms suggestive of GCA. In our study, we have confirmed this trend, with only four patients needing an invasive tool to confirm the diagnosis, with obvious advantages for patients and in terms of costs [4,6]. US has been demonstrated to further improve the diagnostic yield given its significantly higher sensitivity compared to TAB [16]. Indeed, US has the advantage of being non-invasive, allowing a thorough assessment of vessels in their whole length, and permits extending the exam to other cranial or extra-cranial arteries if needed. Moreover, US allows access to the results of the examination instantly to guide further decisions on diagnosis and treatment [4,17]. In our study, a high sensitivity of US reaching 81.98% (95% CI 73.55-88.63%) and specificity of 99.43% (95% CI 96.88-99.99%) was demonstrated. Although our study confirmed a high specificity of US for the diagnosis of GCA, it must be kept in mind that the halo sign has been described in patients with TA involvement due to other diseases, including anti-neutrophil cytoplasm antibodies (ANCA)-associated vasculitis, amyloidosis, and neoplasms, therefore, the US findings must in all cases be correlated with the clinical scenario [18, 19, 20]. The early referral of patients with suspected GCA to a FTA clinic is critical to prevent acute complications, such as permanent visual loss [6,7,21]. In a recent study, we showed that FTA combined with the US of TA and AX significantly reduced the incidence of blindness, mainly due to a decreased diagnostic delay and earlier treatment initiation [8]. In the current study, visual loss occurred in 10.8% of patients with a final diagnosis of GCA, representing a significantly lower frequency compared to the standard care assessment of the disease. The FTA clinics have without doubt changed the prognosis of GCA and the irreversible ischemic damage. Nonetheless, the fear of severe complications such as visual loss and the non-specific nature of the majority of symptoms of LVV also leads to a relevant proportion of patients being referred to the FTA who do not receive a final diagnosis of GCA. In our cohort, only 39% of first referrals had a final confirmed diagnosis of GCA. We analyzed the presenting symptoms leading to the referral to the FTA to identify relevant clinical features to help improve our evaluation of the pre-test probability of GCA and distinguish patients without vasculitis. We demonstrated that jaw claudication, tongue claudication, scalp tenderness, and bilateral visual loss are the most specific symptoms to distinguish GCA from other conditions. Interestingly, headache is not reported in at least 33% of patients with a final diagnosis of GCA, underlying the need to keep a high level of suspicion even in patients without the most frequent cranial symptoms of the disease. Especially for patients with extra-cranial GCA, the referral to FTA clinics might be further delayed by the non-specific nature of the reported symptoms. Systemic manifestations, including \(\geq\)2 general symptoms, although non-specific, were significantly more frequent in the GCA group. Furthermore, patients with a final diagnosis of GCA far more frequently had a combination of different cranial or extra-cranial symptoms.