Assessing elementary lesions in gout by ultrasound: Results of an OMERACT patient-based agreement and reliability exercise

Objective. To test the reliability of the consensus-based ultrasound (US) definitions of elementary gout lesions in patients. Methods. Eight patients with microscopically proven gout were evaluated by 16 sonographers for signs of double contour (DC), aggregates, erosions, and tophi in the first metatarsophalangeal joint and the knee bilaterally. The patients were examined twice using B-mode US to test agreement and inter- and intraobserver reliability of the elementary components. Results. The prevalence of the lesions were DC 52.8%, tophus 61.1%, aggregates 29.8%, and erosions 32.4%. The intraobserver reliability was good for all lesions except DC, where it was moderate. The best reliability per lesion was seen for tophus (κ 0.73, 95% CI 0.61-0.85) and lowest for DC (κ 0.53, 95% CI 0.38-0.67). The interobserver reliability was good for tophus and erosions, but fair to moderate for aggregates and DC, respectively. The best reliability was seen for erosions (κ 0.74, 95% CI 0.65-0.81) and lowest for aggregates (κ 0.21, 95% CI 0.04-0.37). Conclusion. This is the first step to test consensus-based US definitions on elementary lesions in patients with gout. High intraobserver reliability was found when applying the definition in patients on all elementary lesions while interobserver reliability was moderate to low. Further studies are needed to improve the interobserver reliability, particularly for DC and aggregates.