Background/Purpose: The detection of subclinical synovial inflammation (“silent synovitis”) would be of critical importance for the detection of rheumatoid arthritis (RA) in its earliest pathophysiological stage (”pre-RA”), and it has been suggested that ultrasound (US) with power Doppler (PD) can be a useful technology to achieve this. Fluorescence optical imaging (FOI, “Rheumascan”) is a novel imaging modality for the hands based on the use of an intravenous fluorescence dye that allows imaging of the hands with increased optical signal in areas of high perfusion and/or capillary leakage. Here, we investigated whether FOI could be used in lieu of US/PD for ascertaining subclinical syovitis in the hands and wrists.

Methods: A total of 748 joints of the bilateral hands and wrists, including 3 wrist joints, 5 MCPs, 5 PIPs, and 4 DIPs in 22 patients (15 female, 7 male) aged between 19 and 84 years old, with inflammatory arthritis (RA:9, JIA, gout psoriatic arthritis, SLE, and other diagnoses, 1-2 each) were examined clinically, by US and FOI. Joints were considered clinically inflamed when both swollen and tender, and non-inflamed otherwise. Ultrasound was considered positive for synovitis if both thickening on grey scale and Doppler signal were present. FOI was considered positive by visual inspection of the images.

Results:  Out of 748 joints, 71 (9%) were considered inflamed by clinical examination and 677 were not. Of the clinically non-inflamed joints, exactly 100 were inflamed by US. Of these joints, 80 were inflamed by FOI and 20 were not. Thus, the sensitivity of FOI for detecting sub-clinical synovitis when defined as a positive US in the absence of clinical inflammation was 80%. Out of the 577 joints that were non-inflamed clinically and non-inflamed by ultrasound, 26 had inflammation by FOI, yielding a specificity of 95%.

Conclusion: Under the assumption that US can correctly identify sub-clinical synovitis in clinically non-inflamed joints (using the combination of clinical examination and US as the “gold standard”), the sensitivity of FOI for detecting subclinical synovitis in the hands and wrists is 80% and the specificity 95%. These metrics suggest that it may be a useful tool in the setting of identifying patients with very early synovial inflammation of the hands and/or wrists.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/the-utility-of-fluorescence-optical-imaging-for-detecting-clinically-silent-synovitis-of-the-hands-and-wrists/