Understanding the use of thermography and its ability to predict ultrasound-detected joint inflammation at the metacarpophalangeal joint in patients with rheumatoid arthritis

Objectives To study the correlation of thermography with ultrasonography, and whether thermography can help to predict ultrasound-detected joint inflammation at the metacarpophalangeal joints (MCPJs) in patients with rheumatoid arthritis (RA). Method Maximum, average, and minimum temperatures were recorded by thermography and summed for the MCPJs of each hand. Their relationship with the summed power Doppler (PD) and grey-scale (GS) scores was explored using correlation analysis and simple linear regression. The ability of summed thermographic temperatures to predict summed PD score ≥ 1 and summed GS score ≥ 18 (median score) was studied using receiver operating characteristics (ROC) curve analysis. Intraobserver reliability (single observer) was analysed using intraclass correlation coefficients (ICCs). Results This cross-sectional study examined 810 joints from 81 RA patients. At both right and left MCPJs, all summed thermographic temperatures correlated significantly (p < 0.05) and had significant relationships (p < 0.05) with summed ultrasound scores (for PD and GS, respectively, correlation coefficients ranged from 0.45 to 0.52 and 0.26 to 0.29, and regression coefficients from 0.094 to 0.137 and 0.058 to 0.086). At the bilateral MCPJs, the area under the ROC curves for summed thermographic temperatures in predicting summed PD score ≥ 1 and summed GS score ≥ 18 ranged from 0.80 to 0.82 and 0.65 to 0.66, respectively. ICC values (for 45 baseline MCPJs for which thermographic temperatures were resegmented > 2 weeks apart) were excellent (all > 0.90). Conclusion Thermographic temperatures reflect ultrasound-detected joint inflammation, and appear useful in predicting PD vascularity at the MCPJs of patients with RA.