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Figure 2 Ultrasound synovitis (combined greyscale and power Doppler) scores across the SpA subgroups and healthy controls. SONAR-4 score includes DIP2, DIP3, MTP1 and knee joints. axSpA, axial spondyloarthritis; DIP, distal interphalangeal; HC, healthy controls; MTP, metatarsophalangeal; PsA, psoriatic arthritis; SONAR, SONography in Arthritis and Rheumatism; SpA, spondyloarthritis.
whether US-detected synovitis at PIP joints is caused by the primary inflammatory disease or OA. 35 Additionally, the inclusion of DIP joints in a SpA US score would help to differentiate between patients with PsA and RA. Similarly, the MTP1 joint was included in our final score because we observed significantly more synovitis (GS and PD) at this site in patients with SpA compared with controls. In patients with PsA, Dubash et al reported that the most prevalent site of GS ≥ 2 was the MTP1, followed by MTP2–4 and wrists. They also reported that PD was most prevalent at the wrists (17.5%) and MTP1 (12.6%). 36 There might be a potential overestimation of PsA-related synovitis at the MTP1 joint, as this site is also frequently affected by mechanical stress and OA. Nevertheless, it seems relevant to include the MTP1 joint in the current score since several other studies in PsA also reported significant inflammatory changes at this joint. 10 37 Altogether, to develop the SONAR score, these results indicate that the seven above-mentioned joints (wrist, MCP2, MCP3, hand DIP2 and DIP3, MTP1 and knee)
should be carefully evaluated with US in daily practice when there is a suspicion of SpA (PsA or axSpA). After performing several univariable analyses, we excluded 4/11 joints (PIP2, PIP3, MCP5 and foot PIP3) from the score as these sites were not able to significantly differen- tiate between patients with SpA and controls. Consequently, we propose a novel US score (SONAR- 7). This score examines seven joints bilaterally (including joints in both the upper and lower limbs) and encom- passes a mixture of both small and large joints. These seven sites were included in the final score as they demonstrated significant results in either the univari- able or multivariable regression analyses. Regarding the type of lesion included, we found that both GS (SH/thickening) and PD synovitis differentiated between SpA and HC in the univariable regression anal- ysis, with GS synovitis retaining significant results in the multivariable regression. Consequently, we included both lesions in this quantitative (0–3/joint) score eval- uating seven joints bilaterally, providing a range of 0–84and a threshold of 9 for a suspicion of SpA. This
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Elsehrawy GG, et al . RMD Open 2026; 12 :e006802. doi:10.1136/rmdopen-2026-006802
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