Background Assessment of disease activity in early psoriatic arthritis (PsA) is a challenge because of the potential underestimation of the extent of inflammation by clinical examination and the absence of disease-specific biochemical markers. Sensitive and reliable diagnostic modalities enabling visualization of early inflammatory changes may be useful tools for monitoring the response to therapy.

Objectives Prospective study to analyze the correlation between semiquantitative ultrasound (US) scores and clinical parameters during the course of the disease and to determine the prognostic value of US findings for the overall clinical outcome, defined by EULAR response criteria and minimal disease activity (MDA).

Methods Patients with psoriasis with a recent onset of joint pain (<5 years, visual analogue scale (VAS) pain ≥30/100) who were naive to immunosuppressive treatment were eligible for study inclusion (n=42). To date, 23 patients have completed a minimum of 1 follow-up visit, Patients were evaluated by US and clinically at baseline and after 3, 6 and 12 months. In each patient, a total of 56 joints were examined by US Grey-Scale (GSUS) and power doppler (PDUS). US findings were scored separately on a 0-3 semi-quantitative scale as previously described. US synovitis score was calculated by adding the scores in the GSUS and PDUS modes for all joints examined. Clinical assessment included a joint count of 68 tender and 66 swollen joints, VAS for disease activity (patient and physician), VAS for pain, DAS28-CRP, Leeds dactylitis instrument, HAQ and CRP. Treatment was initiated and modified at the discretion of the primary rheumatologist and dermatologistfollowing international recommendations. EULAR response criteria and criteria for MDA (Coates L. et al.) in PsA were defined for each follow-up period.

Results At baseline, US synovitis score showed a highly significant correlation with TJC68 (r=0,57), SJC66 (r=0,63), physician global activity (r=0,54) and DAS28-CRP (r=0,42). In contrast, the US synovitis score did not correlate with disease duration, PASI, HAQ and patient global activity. Longitudinal data showed a significant correlation between relative changes in the US score and changes in several clinical parameters within 3 month treatment periods: TJC68 (r=0,62), SJC66 (r=0,49) and physician global activity (r=0,42). Clinical responders were more likely to have higher US scores at baseline and showed a significantly higher reduction of the mean US synovitis score between the follow-up-visits compared to non-responders: 25,2 vs. 11,4 (p=0,05) (good EULAR response)/15,3 vs. 12,9 (n.s.) (moderate EULAR response)/12,3 vs. 13,4 (n.s.) (no EULAR response)/13,3 pt. vs. 6,8 pt. (n.s.) (MDA)/16,1 pt. vs. 14,5 pt. (n.s.) (no MDA).

Conclusions US is a useful diagnostic and monitoring tool in early psoriatic arthritis. US findings correlate significantly with parameters of clinical disease activity during the course of treatment. Clinical responders (defined by EULAR response criteria and MDA) showed a higher relative reduction of the US score. Therefore, reduction of inflammatory changes detected by US within a 3-month follow-up period may be predictive for a favourable long term clinical, functional and radiographic outcome - this hypothesis will be further analyzed in the ongoing study.

Disclosure of Interest None Declared