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CT scans show limited diagnostic ability for early gout

Rod Tucker
16 July, 2021  

Single-source dual-energy CT scans successfully identify joint urate crystal deposition but are less accurate for the detection of early gout.

Gout is a common condition that affects between 0.1% and 10% of the world’s population. The condition is characterised by the deposition of monosodium urate in tissues and around the joints and which may contribute to progressive joint destruction. The identification of monosodium urate in synovial fluid relies on tissue aspirates though in recent years, a diagnosis of gout has been increasingly made based on the observation of monosodium urate with the use of the imaging modality, dual-energy CT scans (i.e., dual-energy computer tomography or DECT, scanning), which allows for automatic colour-coding of urate depositions. In 2019, a review of 10 studies concluded that DECT had a high diagnostic accuracy in established gout although the technique has a low sensitivity for detecting the condition in those with recent onset disease. While many studies have relied upon dual-source DECT, the performance of other types of DECT such as single-source rapid kilovoltage switching DECT and dual-scan single source CT has been less well studied. This led to a team from the Department of Radiology, The First Affiliated Hospital of Anhui Medical University, Hefei, China, to retrospectively investigate the diagnostic performance of single-source DECT in patients with suspected gout in the ankles or feet. In addition, the team were interested in the ability of the technology to evaluate urate deposition using a semi-quantitative DECT scoring system. For this scoring system, each scan is divided into four areas and graded based on the maximum amount of urate deposited measured during visual inspection. The DECT derived scores are correlated with urate volumes and enable the differentiation of those with and without gout. For the current study, included patients were those with suspected gout of the feet or ankles and categorised in terms of disease duration as early (< 1 year), middle (1–3 years) and late (> 3 years). All scans were performed with a single-source DECT system, Discovery CT750HD and Revolution CT. The sensitivity, specificity and area under the receiver operating characteristic curve (AUC) were calculated for comparative purposes.

Findings
In total, 196 patients were included; 125 with a mean age of 56.1 years were examined using the Discovery CT750HD and 71 (mean age = 51.7 years) with the Revolution CT. A history of tophus (i.e., deposits of urate) were found in 16.8% of patients and 37 patients were in receipt of urate-lowering therapy at the time the scan. The overall sensitivity, specificity and AUC of single-source DECT in the 196 patients were 38.1%, 95.4% and 0.67 in early-stage group, 62.9%, 100% and 0.815 for the middle group and 77.5%, 87.5% and 0.825 for the late-stage group. Using the Discovery CT750HD, the sensitivity, specificity and AUC for gout diagnosis were 55.5%, 100% and 0.778 in the early stage and values were similar for the Revolution CT and for each disease duration. As might be expected the urate deposition scores were significantly higher for those with a longer disease duration.

The authors concluded that while both single-source DECT scanning showed great promise for accurately detecting monosodium urate, it had limited diagnostic sensitivity for patients with early or short-term gout.

Citation

Shang J et al. Gout of feet and ankles in different disease durations: diagnostic value of single-source DECT and evaluation of urate deposition with a novel semi-quantitative DECT scoring system. Adv Rheumatol 2021