Background/Purpose:

Ultrasound (US) has received an increasing attention in detecting uric monosodium urate (MSU) deposits, and is included in the ACR/EULAR classification criteria for gout. The OMERACT US group has developed definitions for US elementary lesions in gout including double contour (DC) sign (deposits of crystals on the surface of cartilage), tophus (larger hypo-echoic aggregation of crystals, usually well delineated), aggregates (small hyper-echoic deposits) and erosions. MSU deposits may be found in many different regions in an individual with gout but with some predilection sites. The present objective was to asses by US the presence of MSU deposits in a high number of locations known to be involved, and to identify areas to include when screening for gout by US.

Methods:

This includes baseline data from a prospective observational study where patients with crystal-proven gout who presented after a recent gout flare were included (117 patients (mean (SD) 56.9 (14.1) years old, 8.5 (7.3) years disease duration, 93.2% men), all with insufficiently treated serum uric acid level (>360 μmol/L/>6 mg/dl). We performed a systematic extensive assessment with US (GE E9 machine, grey scale 15MHz) to detect MSU deposits, using the OMERACT definitions for DC, tophi and aggregates. The following locations were assessed bilaterally; radiocarpal joint, MCP 2, insertion of triceps and quadriceps, the patellar tendon (divided into proximal and distal), cartilage of distal femur (maximal flexed knee) and the talar cartilage of the tibiotalar joint, the MTP 1 joint as well as the Achilles tendon. Sum of sites with deposits was calculated and correlations were performed by use of Spearman, and frequencies of deposits were calculated as percentages at each site.

Results:

The mean (SD) serum uric acid level was 488 (88) μmol/L. There was no significant correlation between number of sites with deposits and uric acid level (r=0.11), but with disease duration (r=0.25, p=0.007). The table shows that DC was primarily found in MTP1, followed by talar and femoral cartilage. Tophi and aggregates were primarily found in MTP1, followed by distal patellar and triceps tendons. There were no major differences between right and left side. In 21 patients (17.9%) DC was seen on femoral or talar cartilage, but not in the MTP1 joints.

Conclusion:

There is limited knowledge on the primary locations of MSU deposits, and the present study suggests US examinations of MTP1, distal patellar and triceps tendons as well as talar and femoral cartilage to be the most important sites to explore for presence of MSU deposits in patients examined for possible gout.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/where-to-look-for-uric-acid-crystals-results-from-a-norwegian-ultrasound-study/