Giant cell arteritis (GCA) is a rare disease characterized by vasculitis of the large arterial trunks targeting the thoracic aorta and its dividing branches, affecting adults over the age of 50. Vasculitis lesions cause thickening of the arterial wall, visible on temporal artery biopsy (TAB) or vascular imaging (echo-Doppler, angio-CT, angio-MRI, 18FDG PET-CT). This is a severe disease that can lead to blindness. Early diagnosis is essential, so that steroids therapy can be started as soon as possible to prevent complications. Doppler ultrasonography of the temporal arteries provides rapid, non-invasive diagnostic support. However, the recommendations do not specify how soon temporal artery Doppler should be performed after steroids treatment, except that the halo sign would disappear after about 5 days on steroids. Sensitivity seems to be better when the examination is performed early, but the time taken for the halo sign to disappear is unknown. The investigator suggests that the disappearance of the temporal artery halo sign in GCA patients is observed earlier than D14 of steroids treatment usually reported in the literature. He speculates that the sensitivity of the temporal artery Doppler decreases as early as D3 of steroids treatment, and that beyond D7 it is not useful to perform this examination as its sensitivity becomes too low.

Inclusion Criteria:

• Patients aged 50 and over
• Without legal protection.
• Meeting GCA classification criteria as defined by ACR 2022.
• Newly diagnosed with an indication for corticosteroid treatment.
• Have not yet received corticosteroid treatment for GCA.
• No contraindication to corticosteroid treatment.
• Person affiliated with or benefiting from a social security scheme.
• Free, informed and written consent signed by the participant and the investigator (at the latest on the day of inclusion and before any examination necessary for the research).

Exclusion Criteria:

• Patients with a relapse of Giant Cell Arteritis (GCA).
• Patients who have previously undergone a temporal artery biopsy (TAB), including for other reasons.
• Patients who have received oral corticosteroid treatment in the past month or are currently on corticosteroid therapy (excluding hydrocortisone or local corticosteroids).
• Patients with other types of vasculitis that may constitute a differential diagnosis: presence of antibodies against the cytoplasm of neutrophils (ANCA), positive syphilis serology, positivity of an IGRA test (Interferon Gamma Release Assay).
• Patients having received immunosuppressive treatment or biotherapy in the month prior to inclusion. If the patient's condition warrants the use of biotherapy or immunosuppressive treatment, its initiation will be delayed until after Day 7 to avoid interfering with the Doppler procedure.