• Ultrasound is accurate in detecting synovitis, especially at the metacarpal phalangeal joints and the proximal interphalangeal joints.
• While more sensitive than clinical examination, ultrasound is less sensitive than MRI for deeper joints such as the wrist and the knee joints.
• There is a lack of consensus regarding a standardized ultrasound scoring system for synovitis.
• Compared with MRI, ultrasound is less expensive and more portable and has fewer contraindications.
Early recognition and treatment of rheumatoid arthritis leads to reduced inflammation and less joint damage, which results in better long-term outcomes. With current treat-to-target guidelines, it is helpful to have reliable, reproducible diagnostic tools to discover and then monitor treatment for rheumatoid arthritis.
Kaoru Takase-Minegishi and fellow researchers in Japan point out that recent advances have led to the rise of ultrasound and MRI modalities as the tools of choice for diagnosis and monitoring disease activity in patients with rheumatoid arthritis.
“The presence of inflammation observed with US or MRI can be used to predict the progression from undifferentiated inflammatory arthritis to clinical RA,” note the researchers.
The research team sought to compare the accuracy of ultrasound with that of MRI for detecting synovitis in patients with rheumatoid arthritis.
The researchers conducted a systematic review and meta-analysis of the available literature. The primary outcomes were diagnostic test accuracy of ultrasound for synovitis with MRI as the standard. Ultimately, 14 studies were included in the final analysis. Wrists, metacarpal phalangeal joints (MCP), and proximal interphalangeal (PIP) joints were evaluated separately.
• Wrist joint cohorts yielded an ultrasound diagnostic odds ratio (DOR) of 11.6 and an area under the curve (AUC) of 0.81, which suggest good diagnostic test accuracy for synovitis.
• Sensitivity and specificity for wrist ultrasound were 0.73 and 0.78, respectively.
• MCP cohorts yielded an ultrasound DOR of 28 and an AUC of 0.91, which suggest good diagnostic test accuracy for synovitis.
• Sensitivity and specificity for MCP joint ultrasound were 0.64 and 0.93, respectively.
• PIP cohorts yielded an ultrasound DOR of 23 and an AUC of 0.91, which suggest good diagnostic test accuracy for synovitis.
• Sensitivity and specificity for PIP joint ultrasound were 0.71 and 0.94, respectively.
• Knee joint cohorts yielded an ultrasound DOR of 5.3 and an AUC of 0.61, which suggest poor diagnostic test accuracy for synovitis.
• Sensitivity and specificity for knee joint ultrasound reflected no diagnostic value in the test.
Implications for physicians
• Ultrasound is an inexpensive, reproducible, and accurate diagnostic tool for synovitis in patients with rheumatoid arthritis, especially when examining the MCP and PIP joints.
• Ultrasound is probably not the diagnostic modality of choice for knee synovitis.
• Ultrasound is a good option for point of care diagnosis of synovitis in patients with rheumatoid arthritis in the outpatient setting.
• Power Doppler ultrasound showed better diagnostic test accuracy than greyscale ultrasound.
No specific funding was received for this study.
Takase-Minegishi K, Horita N, Kobayashi K, et al. Diagnostic test accuracy of ultrasound for synovitis in rheumatoid arthritis: systematic review and meta-analysis. Rheumatology. 2018;57:49-58.