Ultrasound of the forefeet besides the hands in patients at risk for rheumatoid arthritis: is it worth the effort? A longitudinal cohort study

Abstract

Objective: US can detect subclinical joint-inflammation in patients with clinically suspect arthralgia (CSA), which is valuable as predictor for RA development. In most research protocols both hands and forefeet are scanned, but it is unclear if US of the forefeet has additional value for predicting RA, especially since synovial hypertrophy in MTP-joints of healthy individuals is also common. To explore the possibility to omit scanning of the forefeet we determined if US of the forefeet is of additional predictive value for RA-development in CSA patients. Methods: CSA patients of two independent cohorts underwent US of the hands and forefeet. We analysed the association between RA-development and US-positivity for the full US-protocol, the full US-protocol with correction for gray scale (GS)-findings in the forefeet of healthy and the protocol without forefeet. Results: In total, 298 CSA patients were studied. In patients with a positive US, subclinical joint-inflammation was mostly present in the hands (90-86%). Only 10-14% of patients had subclinical joint-inflammation solely in the forefeet. US-positivity was associated with inflammatory arthritis development in both cohorts, with HRs 2.6 (95% CI 0.9-7.5) and 3.1 (95% CI 1.5-6.4) for the full protocol, 3.1 (95% CI 1.3-7.7) and 2.7 (95% CI 1.3-5.4) for the full US-protocol with correction, and 3.1 (95% CI 1.4-6.9) and 2.8 (95% CI 1.4-5.6) without the forefeet. AUROCs were equal across both cohorts. Conclusion: The forefeet can be omitted when US is used for the prediction of RA-development in CSA patients. This is due to the finding that subclinical joint-inflammation in the forefeet without concomitant inflammation in the hands is infrequent.