Effects of Tofacitinib on Body Composition, Bone Mineral Density and Bone Marrow Adiposity in Patients With Rheumatoid Arthritis: the TOFAT Project

Inclusion Criteria: * Adult patient's ≥18 years old with moderately to severely active Rheumatoid Arthritis (RA) (ACR/EULAR criteria ) * Previously untreated with Janus Kinase (JAK) inhibitors * With an indication for tofacitinib will be eligible. * All patients will have to be treated with tofacitinib either alone or with methotrexate. -Healthy volunteers should be ≥18 years old. Exclusion Criteria: * • treatment with more than three anti-Tumor Necrosis Factor alpha (TNFα). Patients who were receiving anti-TNFα will be required a washout period lasting at least five-half-lives before to start tofacitinib, * previously exposed to JAK inhibitors, * patients who were receiving non-anti-TNFα biologics (abatacept, tocilizumab, sarilumab or rituximab) will be required a washout period lasting at least five-half-lives before to start tofacitinib * Concomitant methotrexate (MTX) will be permitted if started ≥3 months prior to study start and at a stable dose (≤25 mg/week) for ≥4 weeks. * history or discovery of an osteoporotic fracture AND/OR T-score≤-3 if ≥50 years AND/OR Z-score ≤-3 if \<50 years during the screening phase, * current treatment with oral corticosteroids higher than 10 mg prednisone/day, * pathologies or treatments that could affect the bone metabolism (breast cancer with aromatase inhibitors, gastrointestinal malabsorption, stomach cancer, primary hyperparathyroidism, uncontrolled hyperthyroidism…), * weight\> 160 kg, * patients on restrictive d…