A subtask force from the Outcome Measures in Rheumatology (OMERACT) ultrasound working group arrived at unanimous agreement regarding a reliable ultrasound score and definition of enthesitis in patients with spondyloarthritis (SpA) and psoriatic arthritis (PsA), according to findings published in the Annals of the Rheumatic Diseases.

Although several enthesitis definitions and scoring systems exist, each incorporates different ultrasound elementary lesions, which has made the comparison of different studies difficult. Investigators aimed to assess the reliability and utility of potential lesions for the detection of enthesitis in SpA and PsA, with the goal of establishing an accepted universal definition amenable to scoring across studies.

Investigators recruited 5 patients with SpA or PsA to undergo scanning using power Doppler and dynamic B-mode ultrasound at 4 bilateral locations — elbow lateral condyle, inferior and superior poles of the patella, and calcaneal insertion of the Achilles tendon — for a total examination of 40 entheses, performed by 11 rheumatologists blinded to clinical characteristics. Readers were asked to evaluate 9 elementary lesions as present or absent, including enthesophytes, thickened insertion, hypoechogenicity, bursitis, erosions, calcifications, bone irregularities, and Doppler signal inside and around enthesitis.

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Intra- and inter-observer reliability were calculated using kappa values. Each lesion was categorized as structural or inflammatory by the readers, who were also asked to decide which lesions should be included in the final enthesitis definition, with the understanding that only those present in ≥75% of entheses would be considered.

All 5 participants (mean Bath Ankylosing Spondylitis Activity Index, 4.5; mean C-reactive protein, 5 mg/L) were women who were HLA-B27-positive and taking nonsteroidal anti-inflammatory medications.

With the exception of bone irregularities (54%) and enthesophytes (55%), the interobserver prevalence of the 9 elementary lesions was low, with reliability ranging from poor (thickened enthesis kappa, 0.1; 95% CI, 0-0.7) to good (enthesophytes kappa, 0.6; 95% CI, 0.5-0.7). However, after adjustment for low prevalence, kappa values increased for all lesions (median for all components ≥0.8), with bursitis (0.8) and Doppler detection at the insertion (0.9) demonstrating the greatest reliability.

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A total of 16 of the 40 entheses were rated as positive for enthesitis. The finalized global enthesitis definition and scoring system included the following elementary ultrasound components: insertion Doppler signal, erosions, calcifications/enthesophytes (combined into 1 category), increased enthesis thickness, and hypoechogenicity. Structural components included calcifications/enthesophytes and erosions, while hypoechogenicity, enthesis Doppler signal, and increased enthesis thickness were considered inflammatory.

The researchers noted that the current scoring system did not weigh enthesitis severity or activity.

 “This study confirms the ability of [ultrasound] to detect the components that describe an enthesitis and the good reliability (according to the observed prevalence of the lesions) in scoring them,” the authors concluded. They recommended that future trials be conducted to allow for widespread implementation of their scoring system in clinical practice.

This study was supported by an unrestricted grant from AbbVie France.

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Balint PV, Terslev L, Aegerter P, et al. Reliability of a consensus-based ultrasound definition and scoring for enthesitis in spondyloarthritis and psoriatic arthritis: an OMERACT US initiative [published online August 3, 2018]. Ann Rheum Dis. doi:10.1136/annrheumdis-2018-213609