Pilot Study to evaluateThrombomodulin to Rule Out Giant Cell Arteritis (GCA) in Polymyalgia Rheumatica (PMR) Patients. (THROPIQ)

Inclusion Criteria: * Patient who has given oral consent * Patient \> 50 years of age Patients with PPR, meeting ACR/EULAR 2012 criteria: * age \> 50 years at onset of symptoms * inflammatory limb-girdle pain * elevated ESR (\>20 mm/hr) and/or CRP (\> 10 mg/l) * AND Score ≥ 4 points among * Morning stiffness \> 45 minutes (2 pts) * Hip pain or limitation of amplitude (1 pt) * Rheumatoid factor or anti-CCP antibodies negative (2 pts) * Absence of other joint pain (1 pt) Exclusion Criteria: * Patient not affiliated to national health insurance * Patient under legal protection (curatorship, guardianship) * Patient subject to a measure of legal safeguard * Pregnant or breast-feeding women * Adult patient unable to provide consent * Patient having received corticosteroid or immunosuppressive treatment in the month prior to inclusion * Patient with a contraindication to corticosteroid therapy * Patients with an active infection, neoplasia or other inflammatory/autoimmune condition * Patients with late onset rheumatoid arthritis. * Conditions rendering vascular imaging unfeasible or uninterpretable: * For angio-CT: allergy to iodine, renal failure (CKD \<30 mL/min) * For PET scan: unbalanced diabetes NB: only one of the two vascular imaging techniques will be performed, depending on the patient\&#39;s condition and the technical resources available. Secondary exclusion criteria: * Final diagnosis of paraneoplastic PMR * Final diagnosis of RA * Negative PET scan (if performed 72 hours after glucocorticoid introduction)