Ultrasound Synovitis Scoring in RA: EULAR-OMERACT 2025
Clinical Significance of the Scale
The combined EULAR-OMERACT score is designed for standardized ultrasound assessment of synovitis in rheumatoid arthritis. It combines two different but complementary characteristics: gray-scale synovial hypertrophy as a morphological component and power Doppler as a sign of vascularization of the inflamed synovium. The study EULAR-OMERACT 2025 demonstrated that the joint score retains clinical significance when transitioning to the patient level: the cumulative ultrasound burden of synovitis correlates with disease activity and joint damage.
For practice, this is especially important in the dynamic monitoring of RA: the uniform numerical scale reduces variability in descriptions, facilitates comparison of studies, and allows distinguishing minimal, moderate, and severe synovitis not by subjective formulation but by a reproducible combination of GS and PD.
What is Assessed on Ultrasound
The basic unit of the system is an individual joint. For each joint, gray-scale synovial hypertrophy is first assessed, then the intra-synovial Doppler signal, after which a combined class is assigned. Synovitis in this system is not just 'fluid' and is not reduced to a single PD signal: the key gray-scale substrate is hypertrophied synovium.
The gray-scale assessment answers the question of how pronounced the synovial tissue is in the joint cavity. Power Doppler answers the question of whether there is blood flow in this tissue and its relative intensity. Therefore, two joints with the same synovial thickness may receive different final classes if one of them has an intense PD signal.
Combined EULAR-OMERACT Score 0–3
| Final Class | Combination of GS and PD | Interpretation |
|---|---|---|
| 0 | GS 0 and PD 0 | No ultrasound signs of synovitis |
| 1 | GS 1 and PD 0–1 | Minimal synovitis |
| 2 | GS 2 and PD 0–2 or GS 1 and PD 2 | Moderate synovitis |
| 3 | GS 3 and PD 0–3 or GS 1–2 and PD 3 | Severe synovitis |
The logic of the table is simple: pronounced synovial hypertrophy itself raises the final class, but an intense Doppler can also move the joint into a more severe category even with a smaller volume of synovium. This makes the scale sensitive to both the structural component of synovitis and its activity.
Gray-Scale Hypertrophy: Separate Assessment 0–3
| GS Class | Description |
|---|---|
| 0 | No synovial hypertrophy |
| 1 | Minimal hypertrophy filling the angle between periarticular bones without protruding beyond the line connecting their peaks |
| 2 | Hypertrophy protrudes beyond this line but does not spread along the bone diaphysis |
| 3 | Hypertrophy protrudes beyond the line and spreads along at least one bone diaphysis |
The gray-scale part requires a stable scanning plane and the same joint position in repeated studies. The main error is substituting synovial hypertrophy with effusion. Effusion is usually more anechoic and easier to displace or compress with the probe, whereas hypertrophied synovium is less displaceable and less compressible.
Power Doppler: Separate Assessment 0–3
| PD Class | Description of Doppler Signal |
|---|---|
| 0 | No signal |
| 1 | Up to three single signals, or up to two single and one confluent signal, or up to two confluent signals |
| 2 | More than class 1, but the signal occupies less than 50% of the gray-scale synovial area |
| 3 | The signal occupies more than 50% of the gray-scale synovial area |
PD assessment is more dependent on machine settings than GS. For comparability, identical presets, low scale speed, adequate pulse repetition frequency, minimal wall filter, and exclusion of vessel compression by the probe are needed. The protocol should specify that the intra-synovial signal was assessed, not a pericapsular vessel or motion artifact.
How to Record the Result in the Protocol
The optimal record for each joint: 'GS x, PD y, combined EULAR-OMERACT z'. For example: 'Right 2nd MCP: GS 2, PD 1, combined score 2'. This form is transparent for the rheumatologist: it shows what the class is based on — the volume of synovium or vascular activity.
If the study is performed for monitoring, it is important to maintain the same set of joints and the same methodology. When comparing with a previous study, it should be indicated which joints changed class, not just stating 'positive dynamics'. A decrease in PD with preserved GS may indicate a reduction in inflammation activity with residual synovial hypertrophy; a decrease in both GS and PD indicates a more complete ultrasound improvement.
What the 2025 Validation Added
The study EULAR-OMERACT 2025 tested whether the joint score works as a patient-level indicator when results are aggregated across joints. The authors compared ultrasound synovitis with clinical measures of RA activity and joint damage indicators. The study's conclusion: the system demonstrates good construct validity, meaning it measures a clinically relevant phenomenon, not an isolated ultrasound sign.
The practical consequence is that the combined score can be used as a standardized language for ultrasound monitoring of RA. It does not replace clinical activity indices and is not a standalone basis for changing therapy, but it makes the contribution of ultrasound more reproducible and comparable between visits.
Limitations and Typical Pitfalls
- Isolated PD without Synovial Hypertrophy requires verification: a vessel near the capsule, motion artifact, or incorrect area of interest is possible.
- Probe Compression can reduce the PD signal and underestimate the class.
- Different PD Settings between visits make dynamics unreliable.
- Assessment of Only 'Presence/Absence of Synovitis' loses information about severity and does not utilize the 0–3 scale capabilities.
- Comparison of Different Joint Sets at the patient level may distort the total score.
Practical Algorithm
- Select and fix a set of joints for the study.
- In each joint, find the maximum zone of synovial hypertrophy in a standardized projection.
- Assign a GS class 0–3.
- Activate PD with constant settings and assess the intra-synovial signal 0–3.
- Assign the final EULAR-OMERACT class 0–3 using the combined table.
- In the conclusion, indicate joints with the maximum class and class dynamics relative to the previous study.
Frequently asked questions
Is it necessary to specify GS and PD separately if there is a combined score?
Yes. The combined class shows the overall severity of synovitis, but separate GS and PD explain what it is due to: the volume of synovium, vascular activity, or their combination.
Can PD 3 be considered severe synovitis with GS 1?
Yes. In the EULAR-OMERACT system, the combination of GS 1–2 with PD 3 corresponds to a final class of 3, which is severe synovitis.
Does the ultrasound score replace clinical indices of RA activity?
No. The 2025 validation confirms the construct validity of the ultrasound score relative to activity and damage, but the scale is used as a standardized supplement to clinical assessment.