Size matters: observations regarding the sonographic double contour sign in different joint sizes in acute gouty...

In distinguishing urate arthritis (UA) from non-crystal-related arthritides, joint sonography including the detection of the double contour sign (DCS) and hypervascularization using power Doppler ultrasound (PDUS) is an important step in the diagnostic process. But are these sonographic features equally reliable in every accessible joint under real-life conditions?

We retrospectively analyzed 362 patients with acute arthritis and evaluated the DCS and the degree of PDUS hypervascularization in patients with gout and in those with arthritis other than urate arthritis (non-UA). We classified all joints into the groups small, medium, and large. Sensitivities, specificities, positive and negative predictive values (PPV/NPV), and a binary regression model were calculated. We also evaluated the influence of serum uric acid levels (SUA) on the presence of a DCS in each joint category.

Sensitivity of the DCS in gout was 72.5% in the entire cohort, 66.0% in large, 78.8% in medium, and 72.3% in small joints. In wrist joints the DCS sensitivity maxed at 83.3%, with a specificity of 81.8%. The lowest rates of DCS sensitivity were found in gout patients with elbow joint involvement (42.9%). In all joints except metatarsophalangeal joint 1 (MTP-1), the incidence of a DCS increased by the increment of SUA levels above 7.5 mg/dl (p < 0.001). PDUS signals were most commonly found in medium and small joints and were only scarce in large joints, independent of the underlying diagnosis.

In our study we detected different rates of accuracy regarding DCS and PDUS in patients with acute arthritis. The best results were seen in medium-size joints, especially wrists.