Dual-energy computed tomography (DECT) was superior to ultrasound for detecting gouty deposits — particularly at extra-articular locations — in patients presenting with suspected gouty arthritis of the knee. Although ultrasound had limited sensitivity, the double contour sign was the most important and reliable indicator of gouty knee arthritis, according to findings published in the American Journal of Roentgenology.
Despite the high prevalence of gout, few studies have compared ultrasound vs DECT for diagnosis of acute gouty arthritis in the knee. Researchers sought to describe monosodium urate deposition in both the intra-articular and extra-articular spaces of the knee and to evaluate the diagnostic utility of the double contour sign on knee ultrasound.
Between 2015 and 2016, 65 patients (80.0% men; median age, 61.7 years; mean disease duration, 7 years) with a history of gout and clinically diagnosed gouty knee arthritis were enrolled in a prospective trial comparing ultrasound and DECT for confirmation of disease. Ultrasound was performed using a 5- to 18-MHz transducer, and DECT was performed using a dual-source 128-multidetector CT scanner. Radiologists assessed both the intra-articular and extra-articular compartments for urate deposits.
Gout was identified as the final diagnosis by DECT in 52 of the 65 participants (80.0% sensitivity); the other 13 individuals received an alternative diagnosis. In addition, 33 of the 65 patients (50.8% sensitivity) were positively identified on ultrasound as having gout (P =.0016). Of the 52 individuals with gout confirmed by DECT, gout was also detected by ultrasound in 31 (59.6% sensitivity), and 7 of the 13 individuals who did not have gout detected by DECT were also negative for gout on ultrasound (53.8% specificity).
A positive double contour sign was observed on ultrasound in 23 of the 52 patients with positive findings on DECT (44.2% sensitivity), and no double contour sign was observed in 12 of 13 participants with negative findings on DECT (92.3% specificity). Furthermore, 23 of the 33 participants with positive ultrasound findings (69.7%) also displayed this sign.
DECT indicated the presence of extra-articular urate deposits in 44 of 52 people, and ultrasound identified the deposits in only 11 of 52 patients (P <.001). Serum uric acid levels were increased in 29 of the 52 patients with positive findings on DECT (55.8%) and in 20 of the 33 patients with a positive ultrasound examination (60.6%). Uric acid was not considered a good predictor of gouty knee arthritis vs DECT.
The researchers noted that joint fluid aspiration was not performed on all participants. Other study limitations included the inability to assess deep knee structures using ultrasound; use of only one radiologist to evaluate each modality, preventing interobserver correlation calculations; and possible urate crystal deposition below the DECT threshold, secondary to inclusion of patients with acute onset gouty arthritis of the knee.
Ultrasound was valuable for the detection of gouty knee arthritis; however, DECT was the superior modality, with a higher sensitivity for identifying urate deposition, especially extra-articular urate deposits. The authors concluded that, “[ultrasound] can be used for primary screening and DECT can be used for displaying disease extent.”
Strobl S, Halpern EJ, Ellah MA, et al. Acute gouty knee arthritis: ultrasound findings compared with dual-energy CT findings. AJR Am J Roentgenol. 2018;210(6):1323-1329.