The Outcome Measures in Rheumatology (OMERACT) Ultrasound Working Group developed a new definition for ultrasound-visualized aggregates in gout lesions and validated a semi-quantitative scoring system for aggregates, tophus, and double contour sign ultrasound lesions that are indicative of monosodium urate (MSU) depositions in patients with gout, according to study results published in Seminars in Arthritis and Rheumatism.
Despite the inclusion of ultrasound in the OMERACT classification criteria for visualizing MSU depositions, no consensus exists on scoring ultrasound gout lesions. The objectives of the current study were to develop a new definition of aggregates to improve reliability of the gout lesion, establish a new consensus-based scoring system for ultrasound gout lesions, and assess intra- and inter-reader reliabilities accordingly.
Using a Delphi process for establishing group consensus, 24 of the 37 rheumatologists who were invited to participate reviewed hyperechoic lesions to distinguish between small aggregates, which were previously found to have low reliability in ultrasound identification, and larger tophus depositions. Based on these assessments, successive rounds of aggregate definitions were sent to participants until an agreement of greater than 75% was reached.
A novel, semi-quantitative scoring system, in which ultrasound lesions were graded in severity from 0 to 3, was used to assess the reliability of the new aggregate definition. Rheumatologists were sent scored static images and asked to state their level of agreement with the absence (grade 0-1) or presence (grade 2-3) of aggregates using a Likert scale (1-5). The semi-quantitative scoring system was also tested for aggregate, tophus, and double contour gout lesions for all grades (grade 0-3) using the Delphi process and Likert scale agreement.
The new consensus definition for aggregates was, “Bright hyperechoic, isolated spots too small to fulfil the tophus definition and characterized by maintaining their high degree of reflectivity when the insonation angle is changed.”
Kappa (κ) analysis of intra- and inter-reader reliability supported the scoring of aggregates using the new definition (κ=0.71 and 0.61, respectively).
During the re-definition of aggregates, an overarching principle was also established, which stated, “The aggregates can only be scored in a patient if other ultrasound features suggestive of gout such as [double contour] and/or tophus are present/have previously been present at patient level and if the aggregates are not located inside a tophus.”
Using the Delphi process to assess the semi-quantitative scoring system for aggregate, tophus, and double contour lesions, both intra- (κ=0.74-0.80) and inter-reader reliabilities (κ=0.61-0.67) were found to be good.
Study limitations included low response rates and biased feedback, which are typically characteristic of the Delphi process.
The authors concluded, “This study constitutes the first step towards a novel, reliable, semi-quantitative ultrasound scoring system available to clinicians and sonographers assessing [patients with] gout during urate-lowering therapy. The next step is to assess the reliability of the ultrasound scoring system when tested in a patient-based exercise.”
Christiansen SN, Filippou G, Sicre CA, et al; OMERACT Ultrasound Working Group. Consensus-based semi-quantitative ultrasound scoring system for gout lesions: Results of an OMERACT Delphi process and web-reliability exercise. Semin Arthritis Rheum. Published online January 10, 2021. doi:10.1016/j.semarthrit.2020.11.011