Disparity Between Ultrasound- and Clinical Findings in Psoriatic Arthritis in Remission

Current data indicate limited correlations between Ultrasound- and clinical findings of inflammation (synovitis, tenosynovitis, dactylitis, enthesitis) in psoriatic arthritis (PsA). This can could be in relation with subjective parameters included in composite clinical scores, such as patient's global assessment of disease activity. Indeed, there is often a disagreement between patient's and evaluator's global assessments of disease activity in psoriatic arthritisPsA. This can reduce the chance to obtain clinical remission, as defined by such composite clinical scores. Does residual clinical activity assessed by the patient (and not by the evaluator) reflect objective inflammation assessed by ultrasound, or is it in relation with other factors such as fatigue or depression? Objectives: Primary end point: In PsA patients deemed to be in remission according to their assessing consultant rheumatologist (i.e. low physician's global assessment of disease activity), to compare the proportion of patients with persistant persistent ultrasound findings of inflammation (i.e. at least one power Doppler synovitis, tenosynovitis, dactylitis or, enthesitis, "= PD\>0") depending on whether patient and physician's global assessments of disease activity are in agreement or in disagreement (disagreement between patient and physician's global assessments defined by a difference on a VAS ≥ 30/100). Secondary end points : * Proportion of patients in clinical remission or low disease activity according to different clinical composite scores (DAS28-CRP, SDAI, DAPSA, et MDA) and proportion of patients in ultrasound remission or minimal ultrasound disease activity (defined as a PD-score=0 and a PD-score≤1 respectively), in this population. * Comparison of rates of clinical remission and ultrasound remission in patients considered or not in remission according to DAPSA criteria * Correlation between different composite clinical scores (DAS28-CRP, SDAI, DAPSA, MDA) and ultrasound findings (global power Doppler ultrasound sum score combining synovitis, tenosynovitis, enthesitis, then power Doppler ultrasound score for synovitis, tenosynovitis, enthesitis separately) in this population * Correlation between different Patient Reported Outcomes (PROs such as HAQ, PsAID, DLQI) and ultrasound findings (global power Doppler ultrasound sum score combining synovitis, tenosynovitis, enthesitis, then power Doppler ultrasound score for synovitis, tenosynovitis, enthesitis separately) in this population * Evaluation of factors associated with ultrasound remission (PD=0) and with minimal ultrasound disease activity (PD≤1) * Evaluation of factors associated with a disagreement between patient and physician's global assessment of disease activity (patient global assessment on a VAS - physician's global assessment on a VAS ≥ 30/100). Study design: prospective transversal observational study Inclusion criteria: PsA patients fulfilling CASPAR criteria in remission as determined by physician Exclusion criteria: patient simultaneously included in another study with blinded treatment; Steinbrocker class IV patients Outcome measure : Comparison of the proportion of patients in ultrasound remission (i.e. no power Doppler synovitis, tenosynovitis, dactylitis, enthesitis, PD=0) depending on whether patient and physician's global assessments of disease activity are in agreement or in disagreement