Biologics are routinely used for the treatment of rheumatoid arthritis (RA). Adalimumab is a human monoclonal antibody that inhibit the Tumor Necrosis Factor alpha (TNF-alpha). Identification of RA patients who respond to biologics is a challenging goal to avoid unnecessarily, costly and potentially harmful treatment.

The aim of the study is to address if 18 F FDG is a valuable biomarker for the assessment of the clinical response in RA with TNF-alpha blocking agent. Eight patients fulfilling the ACR (American College of Rheumatology) criteria will by enrolled. Patient will receive adalimumab according to the current guidelines i.e. 40mg /14 days sub cutaneously. The decision will stand on a high activity of the disease defined by the DAS 28 (Disease Activity Score) above 5.1. Positron emission tomography will be performed before, 2 and 12 weeks after the begin of the treatment. The response to adalimumab will by assessed by the SUV (standard Unit value) measured on the inflammatory joints of hands, wrist, ankle, feet and knees and compared to measurement of clinical (total swollen and tender joints count) echographic (synovium thickness and power doppler) and chemical biomarkers (erythrocyte sedimentation rate, C reactive protein).

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Inclusion Criteria: - Patients with active Rheumatoid arthritis PR définie selon les critères ACR (1987) (annexe 7) [18], Activité importante de la maladie (DAS 28 > 5,1) (annexe 5) [7], Indication d'un traitement par adalimumab (en accord avec l'A.M.M.), Homme ou femme dont l'âge est supérieur ou égal à 18 ans, Acceptant de participer à l'étude et ayant donné son consentement éclairé, Affiliés ou bénéficiaire d'un régime de sécurité sociale.