Detection of Uric Acid Crystal Deposition by Ultrasonography and Dual-Energy Computed Tomography: A Cross-Sectional Study in Patients with Clinically Diagnosed Gout

SLR - November 2019 - Steven A. Tocci

Reference: Wang, Yu; Deng, Xeurong; Xu, Yufeng; Ji, Lanlan; Zhang, Zhouli. Detection of Uric Acid Crystal Deposition by Ultrasonography and Dual-Energy Computed Tomography: A Cross-Sectional Study in Patients with Clinically Diagnosed Gout. Medicine (Baltimore). 2018 Oct;97(42):e12834. doi: 10.1097/MD.0000000000012834.

Scientific Literature Review

Reviewed By: Steven A. Tocci, DPM
Residency Program: Ascension Wisconsin – Milwaukee, WI

Podiatric Relevance: A common pathology that podiatric surgeons encounter is gout. There are many situations in which gout can be diagnosed clinically. However, this is not true in when determining the extent of gout in joints. Two modalities that have gained momentum are dual-energy computed tomography (DECT) and ultrasonography (US) in imaging crystal deposition in the lower extremity. The aim of this study was to compare the performance of US and DECT in detecting crystal deposition. The US was performed by rheumatologists who were blinded to clinical data and DECT results.

Methods: Sixty (60) consecutive patients between 2012 and 2014 clinically diagnosed with acute or chronic gout underwent both US and DECT scans of bilateral 1st MTP joints, midfoot, ankle and knee. The US and DECT scans were done within three days of each other. Synovial fluid was obtained when possible. Two board certified radiologists were blinded to clinical diagnosis as well as US findings when analyzing DECT. Both were analyzed against synovial fluid analysis to detect sensitivity and specificity.

Results: The authors found that US can detect significantly more patients with crystal deposition than DECT (81.7 percent vs. 56.7 percent, respectively). The frequency of urate crystal deposition detected by US at the first MTP, knee, and ankle joint was 56.7 percent, 63.3 percent and 51.7 percent, respectively. Uric acid deposition was found by DECT in the first MTP, knee and ankle in 48.3 percent, 45.9 percent and 43.3 percent, respectively. The overall positivity of crystal deposition detected by US was significantly higher in US (81.7%) vs. DECT (56.7 percent). Both were equal at 99 percent specificity; however, US was significantly more sensitive at 97 percent vs. 62 percent for DECT.

Conclusions: The authors conclude that when performing imaging studies in diagnosing gout, US should be considered the first line choice due to the high specificity and higher sensitivity than DECT. This could be because DECT studies can have artifact, DECT has higher sensitivity in acute gout (when the study only had 13.3 percent of patients with active arthritis), and that DECT can miss smaller tophi, which are common in the first MTP joint. Another limitation of the study is that only 55 percent of the patients had synovial fluid analysis, which could skew the numbers. Based on this study, both US and DECT are viable imaging options when diagnosing gout, with US seemingly superior due to its significantly higher sensitivity with comparable specificity.