Background The OMERACT Ultrasound scoring system (USSS) of joint in RA has been shown to be reliable and sensitive to change when used in clinical trial setting. However it is unclear whether this reliability is also achieved in clinical daily practice among Rheumatologists performing US in a non-research setting and using different machines.

Objectives To assess agreement between non-research sonographers in scoring synovitis using the OMERACT USSS and using the scoring of an OMERACT expert as gold standard. To assess the reliability of the USSS by using different US machines.

Methods First an OMERACT US expert presented the scoring method and supervised a training session. The wrist, MCP 2 and 3 joints of the left hand (dorsal aspect) of 3 RA patients were then successively evaluated by 9 Rheumatologists with 3 different US machines: Hitachi Arietta = H, GE Logic E9 = G, Esaote MyLab 7= E. The USSS included B-mode acquisition of synovial hypertrophy (SH), joint effusion (JE) and bone erosion (BE), and Power-Doppler (PD) activity. JE, SH and BE were scored binary; SH and PD were score semi quantitatively (0 to 3), by both the 9 participating Rheumatologists and the OMERACT US expert. The agreement between each participant with the scoring of the OMERACT US expert was quantified by proportions. The inter-US machine reproducibility was assessed by kappa statistics for discrete variables and weighted kappa's for ordinate.

Results The 3 joints of 3 patients each were evaluated on the 4 US items (SH, JF, BE, PD) on a different US machine. So 27 values were obtained for each joint within each item. The percentages of exact agreement (PEA) between these 27 values and the scores of the OMERACT US expert were calculated and ranged between 33% (9/27) for SH-MCP3, 37% for JF-MCP2 and PD-Wrist, 41% for SH-wrist, 48% BE-MCP3, 52% PD-MCP3, 56% PD-MCP3, 59 JF-wrist and BE-MCP2, 63% JF-MCP3, 67% SH-MCP2 and 78% (21/27) for BE-wrist. For the inter-US machines reproducibility, kappa between the 3 machines was calculated on 9 data (3 patients x 3 joints). The reliability was low for detecting JE ≤0.211. Acceptable reliability among machines was found for SH, BE and PD (table 1).

Conclusions Non OMERACT-expert Rheumatologists can apply the USSS, and this score works well across different machines. The difference among machines and sonographers is mostly captured by the low reliability of JE. The OMERACT USSS could be used by sonographers in their everyday clinical practice to evaluate the activity of RA patients. Further studies in clinical-based settings will allow to define more precisely the applicability of this scoring system.

Disclosure of Interest None declared