Inclusion Criteria:  Major patient (age ≥ 18 years) Patient with RA according to American College of Rheumatology (ACR) / European Congress of Rheumatology (EULAR) 2010 or ACR 1987 or patient with PsA according to ClASsification criteria for Psoriatic ARthritis (CASPAR) criteria Patient undergoing treatment with methotrexate (MTX) (oral or injectable) initiated for at least 3 months. Naïve patient of biotherapy or tsDMARD and requiring the introduction of a first bDMARD or tsDMARD due to the activity of the disease. Patient informed and accepting the computer processing of his/her medical data and informed of his/her rights of access and rectification.  Exclusion Criteria:  Patient participating in an interventional study in rheumatology Patient with axial spondyloarthritis (for patients with PsA)