Assessing the sensitivity to change of the OMERACT ultrasound structural gout lesions during urate-lowering therapy

Objectives: To evaluate the sensitivity to change of ultrasound structural gout lesions, as defined by the Outcome Measures in Rheumatology (OMERACT) ultrasound group, in patients with gout during urate-lowering therapy (ULT). Methods: Ultrasound (28 joints, 26 tendons) was performed in patients with microscopically verified gout initiating or increasing ULT and repeated after 3 and 6 months. Joints and tendons were evaluated by ultrasound for presence of the OMERACT structural gout lesions - double contour sign (DC), tophus, aggregates and erosion - scored binarily. A sum score was calculated at patient and lesion level. Changes at 3 and 6 months in patient sum scores and lesion scores at different locations were evaluated. Results: 50 patients (48 men), mean age 68.9 (range, 30-88) years, were included. Ultrasound showed a statistically significant decrease in DC and tophus sum scores from 0 months (3.16 and 2.68, respectively) to 3 months (2.33 and 2.43) and 6 months (1.34 and 1.83) (all p<0.002). The aggregate sum score only decreased significantly from 3 to 6 months (6.02 to 5.02, p=0.002), whereas erosion sum score remained almost unchanged. All four structural lesions were most commonly found in metatarsophalangeal (MTP) 1 joints (>1 lesions bilaterally), and furthermore MTP2-4 and knee joints were common sites especially for DC. Likewise, these regions were the locations with most pronounced changes in scores. Conclusion: Ultrasound assessment of the OMERACT structural gout lesions scored binarily seems to be a useful tool for monitoring urate depositions during ULT. Particularly DC and tophus showed sensitivity to change after only 3 months of treatment.