This study aimed to evaluate the positive rate and prognostic significance of superb microvascular imaging (SMI) in rheumatoid arthritis (RA) patients in remission with normal C-reactive protein (CRP) levels and erythrocyte sedimentation rates (ESR).
The study enrolled 112 RA patients, and ultrasound (US) assessment was performed on 28 joints of each patient.
The SMI signal-positive rates for each joint were: metacarpophalangeal (MCP) joints: 20.5%, wrist joints: 43.8%, metatarsophalangeal (MTP) joints: 17.0%, and other foot joints: 25.0%. Investigation of the prognostic significance of the SMI signal in each joint revealed that only in the MTP joints was the total score of the SMI signal in the patients with relapse significantly higher than that in the patients with remission (P = 0.01). Comparison of the receiver operating characteristics curves for predicting relapse showed that the area under the curve (AUC) of the MTP joints was the highest (AUC = 0.66) of the investigated joints. The optimal threshold for the total MTP SMI score was 1 (accuracy = 83.3%). Positive/negative data of the SMI signal in the MTP joints were not significantly associated with the values of conventional disease activity markers.
In RA patients in remission with normal CRP and ESR levels, the percentage of positive SMI signal was highest in the wrist joints. However, the accuracy of the SMI signal for predicting relapse was greatest for the MTP joints, suggesting that US assessment of the MTP joints by SMI is useful for predicting relapse in these patients.