The primary aim of the study was to evaluate whether rheumatoid arthritis (RA) patients considered to be in remission according to clinical criteria sets still had persisting ultrasound (US) synovitis. We further intended to evaluate the capacity of our US score to discriminate between the patients with a clinically active disease versus those in remission.

This is an observational study nested within the Swiss Clinical Quality Management in Rheumatic Diseases (SCQM) rheumatoid arthritis cohort. A validated US score (SONAR score) based on a semi-quantitative B-mode and Doppler (PwD) score as part of the regular clinical workup by rheumatologists in different clinical settings was used. To define clinically relevant synovitis, the same score was applied to 38 healthy controls and the 90st percentile was used as cut-off for ‘relevant’ synovitis.

Three hundred and seven patients had at least one US examination and concomitant clinical information on disease activity. More than a third of patients in both DAS28 and ACR/EULAR remission showed significant gray scale synovitis (P=0.01 and 0.0002, respectively) and PwD activity (P=0.005 and 0.0005, respectively) when compared to controls. The capacity of US to discriminate between the two clinical remission groups and patients with active disease was only moderate.

This observational study confirms that many patients considered to be in clinical remission according the DAS and the ACR/EULAR definitions still have residual synovitis on US. The prognostic significance of US synovitis and the exact place of US in patients reaching clinical remission need to be further evaluated.