Polymyalgia rheumatica (PMR) is a rheumatologic condition occurring in patients \> 50 years old, characterized by inflammatory pain of the scapular (shoulder) and pelvic (hip) girdles. PMR is most often isolated but can be associated with giant cell arteritis (GCA), a large vessels vasculitis, in 16 to 21% of case. The main features of GCA are headaches, jaw claudication, visual disturbances, abnormal temporal artery, scalp tenderness associated to elevated CRP and/or ESR. However, GCA could be asymptomatic in particular in case of isolated involvement of large vessels (subclinical GCA). GCA requires high doses of glucocorticoids, compared to isolated PMR, to avoid complications resulting from vascular remodeling (stroke, blindness). Ruling out GCA in PMR patients relies on the performance of some complementary exams that explore cranial vessels as color doppler ultrasound and/or temporal artery biopsy and large vessels that relies on PET/FDG or angio CT scan. The aim of this study is to identifie serum biomarkers that could rule out or identifies GCA in patients with PMR features. Ultimately, if biomarkers are identified, this could allow to select PMR patients in whom complementary exams are needed or not. For this study, investigators chose to explore thrombomodulin. Thrombomodulin is a protein that is increased in the circulating blood during vascular inflammation, and therefore seems to be a good candidate for distinguish isolated PMR from PMR associated with GCA.