Background Microwave Radiometry (MR) is a rapid, non-invasive method that detects in-depth tissue temperatures. Using joint ultrasound as reference method, in a proof-of-concept study, we have found that an increased temperature at the knee joint detected by MR in the absence of relevant clinical signs reflects the presence of subclinical synovial inflammation in rheumatoid arthritis (RA) (1).
Objectives To test the hypothesis that temperature of small joints assessed by MR correlates to global disease activity levels in RA, a disease in which small joints are primarily affected.
Methods Ten patients with active, untreated RA underwent clinical and laboratory assessments, joint ultrasound and MR of hand and foot small joints (RTM 01 RES microwave computer based system, Bolton, UK) at baseline, as well as 15, 30 and 90 days after treatment onset. Twenty aged-matched healthy individuals served as controls.
Results Using 1248 separate MR-derived recordings from RA patients we created several thermo-scores involving different small joint combinations and compared them with clinical and ultrasound data. The best performing thermo-score involved the sum of temperatures of 16 small joints (2nd-5th metacarpal and proximal inter-phalangeal joints, bilaterally). This thermo-score correlated positively to DAS28 disease activity score (p=0.001), tender joint count (p=0.002), swollen joint count (p=0.001), patient's visual analogue scale (p<0.001), CRP (p=0.040), but not ESR levels, as well as to the standard Ultrasound Score of 7 joints (p≤0.025) (2). The MR-derived thermo-score could also discriminate patients in high [mean (SD) 9.2 (5.6)], moderate [mean (SD) 7.1 (3.5)] and low disease activity/remission [mean (SD) 4.2 (1.8)] (p=0.015), or aged-matched healthy subjects [mean (SD) 5.0 (1.7)] (p=0.002). Moreover, individual changes from baseline to follow-up end mirrored the corresponding DAS28 changes in 7/10 patients.
Conclusions Increased in-depth temperatures of small joints detected by MR, which are indicative of local inflammation, may serve as an additional biomarker in RA. Optimization of MR equipment and technique may result in an objective measurement of RA disease activity in clinical practice.
E. Zampeli, et al. Detection of subclinical synovial inflammation by microwave radiometry. PLoS ONE. 2013;(8)5:e64606.
Backhaus M, et al. Evaluation of a novel 7-joint ultrasound score in daily rheumatologic practice: a pilot project. Arthritis Rheum. 2009;61(9):1194–201.
Disclosure of Interest None declared