Introduction
Rheumatoid arthritis (RA) is an autoimmune disorder characterized by polyarticular inflammation and pannus formation, leading to joint destruction and severe disability [
1,
2]. Remission or low disease activity is the ultimate aim for the treatment of RA [
3,
4]. Moreover, in the past few years, several remission criteria have been established including clinical and biological criteria [
5]. However, several studies have shown infra-clinical synovitis and disease exacerbation has persisted in patients who achieved clinical remission [
6]. Thus, it is important to identify true remission in RA patients.
Imaging modalities, such as magnetic resonance imaging, have been reported to detect persistent inflammation in RA patients in clinical remission; however, they require contrast enhancement [
7,
8]. In addition, power Doppler imaging (PDI) can detect modifications in synovial vascularity but it is not very sensitive to microvascular patterns and low blood flow velocity [
9]. Superb microvascular imaging (SMI) is a recent innovative and effective ultrasound (US) Doppler modality, which can visualize low-velocity flow in microvessels. SMI uses a new adaptive algorithm to extract flow signals from large to small vessels and has been used in the diagnosis of breast, thyroid, and urinary tract infection [
10‐
13]. Moreover, SMI can detect synovial inflammation in rheumatic diseases [
14]. However, to date, the utility of SMI for evaluating hand joint lesions in patients with RA in clinical remission has not been reported.
The present study aimed to investigate SMI signals in the hand joint of patients with RA in clinical remission and compare the findings with those of PDI. We also aimed to demonstrate the value of SMI for identifying true remission in RA.
Discussion
RA, characterized by erosive synovitis, causes irreversible bone damage and loss of function. Thus, remission is important for RA patients and persistent subclinical synovitis in RA patients who achieve clinical remission highlights the importance of true remission [
17]. In the present study, we showed that SMI, a new microvascular flow imaging modality, was more sensitive than PDI for detecting synovial vessel signals of the hand joint in RA patients who achieved clinical remission, suggesting that SMI has great potential for improving diagnostic accuracy in evaluating RA remission.
Although the 2011 ACR/EULAR remission criteria have been developed as guidelines for clinical remission, several studies have proposed the use of imaging remission [
17,
18]. A recent study showed that in RA patients with clinical remission, power Doppler activity was demonstrated in the dominant hand and wrist in approximately half of the patients via US examination and the risk of recurrence was 4.5 greater for those with power Doppler positivity than for those with power Doppler negativity [
19]. In addition, the recurrence rate of RA in patients who achieved imaging remission was significantly lower than that of patients who did not achieve imaging remission [
20]. Our present results showed that in the 10 healthy volunteers, SMI and PDI signals were both scored 0, while in 26 RA patients with clinical remission, the imaging remission rate was 65.4% by PDI and only 42.3% by SMI, consistent with the previous study. Thus, imaging remission could be used to improve the prognosis of RA patients.
Our results further showed that SMI detected more synovial blood flow signal in the 572 hand joints compared with PDI, and improved the blood signal classification to some extent, suggesting that SMI could be more sensitive than PDI for detecting synovitis of the hand joint in RA patients with clinical remission. The moderate inter-observer agreement between PDI and SMI indicates that SMI is a feasible and reliable technique. In recent years, SMI has been reported to allow the visualization of low-velocity flow in microvessels excluding the use of contrast agents, high costs, and invasiveness [
21]. Moreover, several studies have reported that SMI, compared to PDI, significantly improved the detection of blood flow signal and synovial inflammation within the joints in RA patients [
13,
14]. And our present study is the first to evaluate SMI in RA patients with clinical remission. Compared with PDI, SMI significantly improved the detection of synovial blood flow signals.
In our study, a patient was classified as having Grade 1 synovial blood flow by PDI but was classified as Grade 0 by SMI. We found the patient was in the motor neuron obstacle treatment center in our hospital and had a history of RA. Thus, because of the interference of the tissue movement, PDI might have produced the pseudo-image. PDI is an important method for evaluating RA synovitis and for detecting vascularity in the joint of RA patients [
22‐
24]. However, it is limited in the detection of microvascular patterns and low blood flow velocity [
25]. Our results indicated that SMI does not have this PDI limitation and is of great value for identifying true remission in RA patients.
Our present study has several limitations. First, the sample of patients was relatively small. Second, we just only detected wrist, proximal interphalangeal, and metacarpophalangeal joints to asses hand joint lesions. Third, the hand joint synovitis alterations were graded only based on the PDI or SMI score, without contrasting with the pathology.
In conclusion, our results suggest that SMI is more sensitive than PDI for the detection of hand joint synovitis in RA patients who have achieved clinical remission, and could aid RA patients to achieve true remission. Further studies are needed to validate the role of SMI in improving diagnostic accuracy in RA remission.
Compliance with ethical standards