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

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.


Eligibility Criteria:
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)

Patient with suspected GCA requiring diagnostic work-up. Suspicion of GCA will be based on:

* The presence of at least one clinical sign of GCA (temporal headache, temporal artery abnormalities, jaw claudication, scalp hyperesthesia, visual disturbance).
* OR the presence of a significant inflammatory syndrome defined by CRP \> 100 mg/L or a ESR \> 100 mm/hr

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)