Gout is a crystal-depositing joint disease caused by a disorder of purine metabolism [1]. The prevalence of GA is increasing every year [2], making it a significant threat to human health. Acute attacks of gout cause severe pain in patients and even affect normal walking, thus causing inconvenience and lowering their quality of life. Early diagnosis and standardized treatment of gout can prevent disabilities, decrease the risk of comorbidities (e.g., cardiovascular and renal diseases associated with hyperuricemia) [3] [4], and reduce the economic burden on patients and society. Therefore, the sensitivity and specificity of diagnostic modalities for gout need to be improved to reduce underdiagnosis and misdiagnosis.
The gout classification criteria published by ACR/EULAR in 2015 [5] proposed that if at least one episode of swelling, pain, or tenderness in a peripheral joint or bursa occurs, the sufficient criteria to be met for the diagnosis of gout include the presence of MSU crystals in a symptomatic joint or bursa (i.e., in the synovial fluid) or tophus. If the sufficient criteria are not met, come to Criteria. The criteria were divided into three parts: clinical, laboratory, and imaging. If the total score is ≥ 8, gout may be diagnosed. However, this classification criterion had some limitations. Regarding the sufficient criteria, joint fluid aspiration is an invasive operation, and the operation of small joints, such as the metatarsophalangeal joint, is difficult; thus, it is not suitable for using as the preferred clinical diagnosis method or as a screening method. For the criteria, there are three first-level indicators, eight second-level indicators, and 19 third-level indicators. It is not convenient for a clinical application. Previous studies have shown that SUA plays a significant role in diagnosing gout [6] [7]. However, SUA can be influenced by various factors like diet and medication intake before testing. Additionally, during an acute attack, SUA may be affected by other inflammatory factors, leading to errors. Hence, imaging examinations are needed to observe changes in the joints. Evidence from ultrasound examinations based on double-contour sign or dual-energy computed tomography (DECT), which revealed urate deposition or at least one bone erosion of the hands and/or feet, as indicated by conventional imaging, was included in the 2015 gout classification criteria. Bone erosion in gout patients indicates that the disease has progressed to the middle or late stages, and thus, conventional imaging is not suitable for early detection and diagnosis of gout. DECT can show the crystallization of monosodium urate deposited in the joint and the destruction of bone in gout patients [8, 9]. Although it has high sensitivity and specificity, it is radiative and expensive and is not found in primary medical institutions. Ultrasound can show cartilage, muscle ligament, and other tissue structures [10], and it is non-invasive, portable, and cheaper than DECT. Some studies have shown the effectiveness of ultrasound in the diagnosis of gout. For example, Cipolletta et al. found that the sensitivity and specificity of the ultrasound DC sign for gout diagnosis were 58% and 89.3%, respectively [11]. However, these studies used the presence or absence of the DC sign as the diagnostic criteria. In 2021, the Rheumatic Outcomes Working Group [12] used the Delphi method to establish a semi-quantitative scoring system (0–3) for evaluating patients with gout. Additionally, in our previous study, we found that the combination of ultrasound DC sign and SUA had a good diagnostic value for gout. However, the study had certain limitations, such as using the presence or absence of DC signs as a diagnostic indicator.
Therefore, we used quantitative tools to quantify the length of the ultrasound DC sign to find the optimal cut-off value of the DC sign for gout. Then, we compared the value of the DC sign alone, SUA alone, and DC sign combined with SUA (in parallel and series) for the diagnosis of gout. We found the diagnostic protocol of gout with the highest diagnostic value and provided a reference for achieving early detection and diagnosis of gout. Our findings can help slow down or prevent disease deterioration and improve the prognosis of patients, thus improving their quality of life.