The sponsor decided to stop financing the study.

During rheumatoid arthritis (RA) (in comparison with control subjects), body composition is altered with a loss of lean body mass, bone mass and an accumulation of fat mass.

Determination of total body fat and particularly its abdominal distribution (visceral adiposity) is important because of the cardiovascular (excess cardiovascular risk), metabolic (insulin resistance, diabetes and dyslipidemia) and bone (increased fracture risk) risks associated with this endocrine organ. Moreover, we do not have data concerning medullary adiposity in RA.

This pilot case-control study will be compare body composition, bone marrow adiposity and bone mineral density in patients with RA versus healthy volunteers.

Inclusion Criteria:

Subjects:

Males and females of age (age ≥ 18 years). Patients with RA according to American College of Rheumatology/EULAR 2010 criteria, Patients who have signed the informed consent

Controls:

Males and females of age (age ≥ 18 years). subjects who have signed the informed consent

Exclusion Criteria:

• Patients who have received more than three anti-TNFinhibitors
• Patients who have previously received a Janus kinase (JAK) inhibitor
• Patients with concomitant therapies as described below :

A combination with methotrexate is allowed if methotrexate is started ≥3 months before the start of the study and at a stable dosage (≤25 mg/week) for ≥4 weeks.

A combination to conventional synthetic DMARDs (csDMARDs) other than methotrexate is not allowed within 4 weeks before and/or during the clinical trial

• Corticosteroid therapy >10mg/d prednisolone equivalent is not allowed
• Intra-articular injections of corticosteroids are allowed if their number is less than or equal to 4
• Intravenous corticosteroid infusions are not allowed
• Immunosuppressants other than methotrexate are not allowed
• History or discovery of an osteoporotic fracture AND/OR T-score ≤-3 if ≥50 years old AND/OR Z-score ≤-3 if <50 years old during the screening phase,
• Corticosteroid therapy ≥ 10mg/d prednisolone equivalent,
• Pathologies or treatments affecting bone metabolism (breast cancer with antiaromatase, digestive malabsorption, stomach cancer, primary hyperparathyroidism, uncontrolled hyperthyroidism...),
• History of radiotherapy on the lumbar spine or the hip studied,
• Patients undergoing hormone replacement therapy (HRT) or patients already under anti-osteoporotic treatment (bisphosphonates, strontium ranelate, teriparatide or denosumab) apart from calcium and/or vitamin D supplementation, Chronic renal failure with creatinine clearance (CKD-EPI formula) ≤ 30 ml/min,

Patients with rheumatoid arthritis and controls