For a prospective pilot study, researchers carried out utilizing microwave radiometry (MR), a non-invasive way of monitoring in-depth tissue temperature, to see if temperature-of-small-joint–derived scores related to metrics routinely used to estimate disease activity in rheumatoid arthritis (RA). Ten patients with active, untreated RA received clinical and laboratory examinations, as well as joint ultrasonography and magnetic resonance imaging (MR) of hand and foot small joints, at baseline and 15, 30, and 90 days following therapy initiation. To compare patient characteristics in consecutive visits, a mixed-model analysis for repeated measurements was utilized. Twenty healthy people of the same age and gender were used as controls.

Several thermoscopes involving different joint combinations were produced using 1,248 distinct MR-derived recordings from patients’ joints. The thermoscope that performed best when compared to clinical and ultrasound data involved temperatures of 16 joints (second to fifth metacarpal and proximal interphalangeal joints, bilaterally). The Thermo score correlated with the 28-joint Disease Activity Score–C-reactive protein, tender, and swollen joint counts, patient’s visual analog scale (all P0.02), and the standard 7-joint ultrasound score (all P<0.03), and could also distinguish 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).

The increased in-depth temperature generated from microwave radiometry, which indicated local inflammation of tiny joints, was used as an additional biomarker in RA. The development of MR-based approaches that were more objective led to objective evaluations of RA disease activity in clinical practice.