Microwave Radiometry-Derived Thermal Changes of Small Joints as Additional Potential Biomarker in Rheumatoid Arthritis: A Prospective Pilot Study

OBJECTIVE: A prospective pilot study was performed using microwave radiometry (MR), a noninvasive method detecting in-depth tissue temperature, to evaluate whether temperature-of-small-joint-derived scores correlate to parameters commonly used to assess disease activity in rheumatoid arthritis (RA). METHODS: Ten patients with active, untreated RA underwent clinical and laboratory assessments and joint ultrasound and MR of hand and foot small joints at baseline and at 15, 30, and 90 days after treatment onset. Mixed-model analysis for repeated measures was used to compare patient characteristics in sequential visits. Twenty age- and sex-matched healthy individuals served as control subjects. RESULTS: Using 1248 MR-derived separate recordings from patients' joints, several thermoscores involving different joint combinations were created. When compared with clinical and ultrasound data, the best performing thermoscore involved temperatures of 16 joints (second to fifth metacarpal and proximal interphalangeal joints, bilaterally). This thermoscore correlated to the 28-joint Disease Activity Score-C-reactive protein, tender and swollen joint counts, patient's visual analog scale (all P ≤ 0.02), and the standard 7-joint ultrasound score (P < 0.03) and could also discriminate patients in high (mean, 9.2 [SD, 5.6]) or moderate (7.1 [SD, 3.5]) versus low disease activity/remission (4.2 [SD, 1.8]) (P ≤ 0.01) or healthy subjects (5.0 [SD, 1.7]) (P = 0.002). CONCLUSIONS: Microwave radiometry-derived increased in-depth temperature indicative of local inflammation of small joints may serve as an additional biomarker in RA. Optimization of MR-based methods may result in objective assessments of RA disease activity in clinical practice.