SMI seems more sensitive than PDI for detecting hand joint lesions in RA in clinical remission PDI, and could aid the achievement of true remission in RA patients. 

Rheumatoid arthritis (RA) is an inflammatory disorder characterized by poly-articular inflammation and pannus formation, results in joint destruction and severe disability. The primary goal for the treatment of RA is the remission or low disease activity. The number of remission criteria has been established in the past few years such as clinical and biological criteria. However, several studies have shown infra-clinical synovitis, and disease has persisted in patients who achieved clinical remission. Thus, it is essential to identify the actual reduction in RA patients.

Imaging techniques, such as magnetic resonance imaging (MRI), have been suggested to detect persistent inflammation in RA patients; however, they require contrast enhancement. Also, power Doppler imaging (PDI) can detect modifications in synovial vascularity, but it is not very sensitive to micro-vascular patterns and low blood flow velocity. Another is the superb micro-vascular imaging (SMI), which is a new innovative and effective ultrasound (US) Doppler modality, which can visualize low-velocity flow in micro-vessels. Moreover, SMI can detect synovial inflammation in rheumatic diseases. However, to date, the utility of SMI for evaluating hand joint lesions in patients with RA in clinical remission has not been reported.

Rationale behind research:

The utility of SMI for evaluating hand joint lesions in patients with RA in clinical remission has not been reported till date.

Therefore, the present study was conducted to investigate SMI signals in the hand joint of patients with RA and to demonstrate the value of SMI for identifying true remission in RA.

Objective:

To investigate SMI signals in the hand joint of patients with RA in clinical remission and compare the findings with those of PDI. 

Study outcomes:

• The wrist, proximal inter-phalangeal, and meta-carpophalangeal joints of both hands were assessed in the axial and longitudinal planes using a 5–14 MHz broadband linear transducer
• The distribution and thickness of the synovium were observed by two-dimensional ultrasound
• Comparison of the remission rate in PDI and SMI
• Comparison of the presence of synovial SMI and PDI signals
• Comparison of the grades by SMI and PDI

Time period: NA

• Comparison of the remission rate in PDI and SMI: PDI showed 9 and 17 patients with synovial inflammation and in remission respectively. However, SMI showed 15 and 11 patients with synovial inflammation and in remission respectively. Moreover, SMI detected micro-vessel flow signal in seven patients diagnosed with clinical remission by PDI. According to these results, SMI revealed that patients with RA in clinical remission did not achieve real remission. The difference in the detection of remission rate between SMI and PDI was statistically significant (χ2 = 5.488, P = 0.019).
• Comparison of the presence of synovial SMI and PDI signals: SMI and PDI further detected the synovial blood flow signal in the 572 hand joints of the 26 patients. SMI detected 106 blood flow signals (18.5%), while PDI detected 50 blood flow signals (8.7%). SMI, compared to PDI, revealed the presence of synovial blood flow signal in a significantly greater number of joints in patients with RA in clinical remission (χ2 = 229.1, P < 0.001).
• Comparison of the grades by SMI and PDI: Regarding SMI, 18.0% of the power flow signals increased from Grade 0–1, while 13.7% increased from Grade 1–2. Moreover, one joint classified as Grade 1 via PDI was classified as Grade 0 via SMI. Inter-observer agreement for the assessment of PDI and SMI semi-quantitative scoring was moderate (Kappa = 0.463, P < 0.01). These results demonstrated that SMI was more sensitive than PDI for detecting synovial vessel signals of the hand joint in patients with RA in clinical remission.

RA is characterized by erosive synovitis which causes irreversible bone damage and loss of function. Thus, remission is important for RA patients. In the current study, it was shown that SMI was more sensitive than PDI for detecting synovial vessel signals of the hand joint in RA patients who achieved clinical remission. This study also suggested that SMI has excellent potential for improving diagnostic accuracy in evaluating RA remission.

The results of the current research showed that SMI recognised more synovial blood flow signal than PDI in the 572 hand joints. 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 micro-vessels excluding the use of contrast agents, high costs, and invasiveness. Moreover, several studies have indicated that SMI significantly improved the detection of blood flow signal and synovial inflammation within the joints in RA patients. The 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 conclusion, It was revealed that SMI is more sensitive than PDI for the detection of hand joint synovitis in RA patients who have achieved clinical remission. Further studies are needed to validate the role of SMI in improving diagnostic accuracy in RA remission.