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

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.