The OMERACT Ultrasound Task Force — Status and Perspectives

1. Intra- and interobserver reliability of ultrasound detection and scoring of synovitis in different RA joints

The group presented the intra- and interobserver reliability results of an exercise for scoring synovitis in non-MCP RA joints. After a consensus session on a synovitis scoring system at the joint level and training on images, 6 RA patients were scanned by 12 observers (2 rounds). The following joints were included: PIP, wrists, knees, tibiotalar, and MTP joints. Intra- and interobserver reliability for detecting and scoring effusion, synovial hypertrophy, PD signal, and PD ultrasound (PDUS) global synovitis (joint-level) were assessed according to OMERACT rules and usual ultrasound practice using standard κ-coefficient and weighted κ-coefficient with absolute weighting [κ(w)] for semiquantitative grades. According to Landis and Koch¹⁴, κ values < 0.40 were considered poor, 0.40–0.60 moderate, 0.60–0.80 good, and 0.80–1 excellent. The results showed a moderate to excellent intraobserver reliability (κ-coefficient range 0.43–0.98) and a moderate to good interobserver reliability (κ-coefficient range 0.49–0.76) for detection of synovitis components (i.e., effusion, synovial hypertrophy, and PD signal) and grading. In addition, intra- and interobserver reliability for both PDUS global synovitis according to OMERACT rules and usual ultrasound clinical practice were good to excellent (κ-coefficient range 0.58–0.86). This demonstrated that OMERACT rules for PDUS scoring of MCP synovitis were valuable for detecting and scoring synovitis in other joints, and they are now implemented in usual ultrasound practice.

2. Ultrasound-based global synovitis score in RA (RA GLOSS)

Moving from joint level to patient level, the group developed an OMERACT ultrasound global synovitis score. For this objective, further evaluation is needed of how many and what joints should be assessed and how to produce a cumulative score. The results of a systematic review in the field of previous ultrasound scoring systems of synovitis in RA were presented (e.g., joint studied, grading used, construct and predictive validity, discrimination, and feasibility) during the Sharp symposium¹⁵. The results from 2 published multicenter longitudinal studies were discussed in more detail. The first, from Naredo and colleagues, compared an ultrasound 44-joint count with a number of reduced counts. It concluded that a 12-joint count was feasible and sensitive to change¹⁶. The second, from Backhaus and colleagues, proposed a 7-joint synovial recess count¹⁷. Both reduced joint counts demonstrated good responsiveness; however, correlation between ultrasound scores and clinical and laboratory findings varied according to the number and size of joints examined. The group agreed that both reduced joint counts required further testing in other multicenter longitudinal studies that also applied the recently devised OMERACT scoring system. For this purpose, a multicenter international study is under way in order to test, first, the sensitivity to change of the OMERACT synovitis scoring system at joint level, and second, to validate a reduced joint count (12 or 7 joints).

During the group discussions and feedback session, a need was expressed to develop the RA GLOSS systems by separating diagnostics from monitoring. For each system, it would be important to know what ultrasound findings and which joints should be assessed. For diagnosis, a large number of joints might need to be assessed, while for monitoring a smaller number is required.

3. Spondyloarthritis-associated enthesitis systematic review and Delphi definition exercise

A number of scoring methods for the peripheral enthesitis in SpA have been described^18,19,20,21, with limited data on their psychometric properties. Our group focused on standardization of peripheral enthesitis scores. Preliminary work on standardizing ultrasound enthesitis had already been performed by some members of the group^22,23, and this was used as a starting point. A systematic literature review of definition of enthesitis and its component lesions was presented during OMERACT 10. The results showed that most studies used variable definition of enthesitis and its components, making comparison of results difficult. Doppler assessment was included in only a few studies. Reliability, sensitivity, and specificity, and responsiveness were assessed in a minority of studies. A number of enthesitis scoring systems at the patient level have been used but all need consensus and validation. In order to produce a consensual definition of ultrasound enthesitis and elementary components, a Delphi exercise was conducted; the exercise focused on ultrasound elementary lesions and definitions among group members (26 ultrasonographers). The Delphi questionnaire included 4 main areas: (1) Definition of normal ultrasound enthesis and other anatomical structures; (2) Which lesions in GS and PD to include; (3) Ultrasound definition of elementary lesions; and (4) Which lesions reflect inflammation and damage. There was high agreement (> 80%) for definitions of normal enthesis and normal bursa and for separating both. There was also high agreement for assessing the following ultrasound elementary lesions: hypoechogenicity and increased thickness of tendon insertion, enthesophytes, calcifications, erosions, and Doppler signal at enthesis insertion.

The number of entheses to evaluate was discussed but it was suggested that we should evaluate 6 bilateral areas. These included quadriceps insertion, patellar tendon (proximal and distal), Achilles tendon, plantar fascia, and lateral epicondyle. In terms of scoring systems, agreement was obtained to develop one for diagnostic purposes and one for monitoring.

4. Preliminary results of an enthesitis intra- and interobserver reliability exercise in SpA patients

The group presented the intra- and interobserver reliability results of an exercise for detecting elementary components of enthesitis in SpA patients. Prior to this exercise, a consensus session on which lesions and sites to include and a training session on images were conducted. Six SpA patients were scanned by 12 observers (2 rounds). The assessed elementary components were as follows: cortical erosions, enthesophytes, increased thickness, hypoechogenicity, PD at cortical insertion, PD outside insertion, bursitis, and calcifications. The following bilateral sites were assessed for the presence of the above components and global enthesitis: epicondyle, Achilles tendon, and patellar ligament (both insertions). Intra- and interobserver reliability for detecting the above components were assessed using standard κ-coefficient and weighted κ-coefficient, with absolute weighting [κ(w)] for semiquantitative grades¹⁴. The results showed a variable intra- and interobserver reliability for detecting the elementary components (better for PD than for GS). However, enthesitis as global definition was more reliable than single components (interobserver κ-coefficient, 0.67; intraobserver κ-coefficient range 0.45–0.80).

The results of an additional Web-based intra- and inter-reader reliability exercise on ultrasound detection of SpA enthesitis were also presented. We tested the elementary components and the definition of enthesitis in a large group of sonographers (18 participants, 120 ultrasound images). The results were variable but comparable to the reliability exercise in patients (interobserver κ-coefficient, 0.61; intraobserver κ-coefficient range 0.20–0.70).

5. Preliminary results of a Delphi definition exercise in hand OA and subsequent reliability exercise

The ultrasound group had previously decided to focus on standardization of joint-related pathologies in OA. After a systematic review of the literature²⁴, an OMERACT/OARSI US sub-task force focused on hand OA. A Delphi exercise focusing on ultrasound elementary lesions and definitions in OA was conducted among group members (21 sonographers). The Delphi process aimed at reaching consensus on ultrasound elementary lesions, definitions, and ultrasound scanning technique. The results showed high to good agreement (> 80%) for evaluating cartilage, osteophytes, bone erosions, cortical irregularities, synovial membrane, and synovial fluid. It was suggested to differentiate ultrasound inflammation and structural damage.

The group undertook 2 reliability exercises in patients with early and late hand OA. There was a high variability in the detection of all elementary lesions in the former exercise, with moderate improvement in detection of some structural damage lesions in the second exercise. The results of these exercises highlighted specific problems of interpretation of cartilage lesions and cortical abnormalities.

Rheumatoid Arthritis; Synovitis

A multicenter international study is currently under way that aims to test the responsiveness of the composite RA OMERACT synovitis scoring system (GS + PD) as applied to different core sets of joints. In addition, group work has begun to focus on the use of ultrasound for evaluating tenosynovitis and structural damage (i.e., bone erosions and tendon damage) in RA. Testing the added value, predictive value in relation to disease-centered (e.g., erosions), and patient-centered (e.g., function) outcomes, as well as the diagnostic value of ultrasound in clinical trials, is a priority objective. Future research directions also include further validation of global ultrasound scoring of synovitis at the patient level for diagnostic purposes and for monitoring in RA.

Spondyloarthritis Enthesitis

After reaching consensus on preliminary selection and definition of the elementary lesions that should be evaluated in peripheral SpA enthesitis, the group is investigating scoring systems at joint level and at patient level with differentiation of elementary lesions useful for activity assessment and damage assessment. The group is also planning further research on the development of reliable and feasible scoring systems for early diagnosis and monitoring of SpA.