Data collection: During each visit, physicians will collect data on the disease and on disease activity: 66 swollen joint counts, 68 tender joint counts, tender entheseal points (Leeds Enthesitis Index) and body surface area of psoriasis. This will allow calculation of most of the usual composite scores of PsA: Arythmetic Mean of Desirability Functions modified (AMDF modified), Disease Activity in PSoriatic Arthritis (DAPSA), clinical DAPSA (c-DAPSA), Minimal Disease Activity (MDA) and Psoriatic Arthritis Disease Activity Score (PASDAS). Well-validated Patient Reported Outcomes will be collected from patients: Patient Global Assessment (PGA), Pain, Health Assessment Quality (HAQ), PSoriatic Arthritis Impact of Disease (PSAID), Psoriatic Arthritis Quality of Life (PsAQoL), 12-Item Short Form Health Survey (SF-12), Patient Acceptable Symptom State (PASS) and Minimal clinically important differences (MCID) as well as the recent Flare questionnaire proposed by GRAPPA. Assessment of disease activity status (i.e. remission or flare) will be performed by both physician and patient using global questions.