Thermography in rheumatoid arthritis: a comparison with ultrasonography and clinical joint assessment

To compare thermography with ultrasonography and clinical joint assessment in patients with rheumatoid arthritis (RA).

Thermography and ultrasonography (power Doppler (PD) and grey-scale (GS) joint inflammation scored semi-quantitatively 0-3) were performed sequentially on both hands of 37 RA patients. Using generalised estimating equations analysis, (a) thermographic parameters (TP) were compared between joints based on their PD and GS joint inflammation positivity/negativity status, while (b) TP and ultrasound-detected joint inflammation were compared between joints categorised by their clinical swelling/tenderness status.

Comparing PD positive versus negative joints, the differences in mean values (95% CI) for TP including maximum (T_max), minimum (T_min), average (T_avg), and T_max minus T_min (T_max-min) temperatures (in °C) were 1.37 (0.86, 1.87), 0.91 (0.46, 1.36), 1.16 (0.67, 1.64), and 0.46 (0.28, 0.64), respectively. Comparing GS positive versus negative joints, the corresponding results for thermography were 1.09 (0.67, 1.52), 0.66 (0.32, 1.00), 0.86 (0.47, 1.26), and 0.45 (0.28, 0.62), respectively. p-Values were all <0.001. The differences in mean values (95% CI) for ultrasound scores, but not for TP, were statistically significant for (a) swollen tender joints (PD: 0.67 [0.39, 0.96], p<0.001; GS: 0.86 [0.54, 1.18], p<0.001) and (b) swollen non-tender joints (PD: 0.46 [0.07, 0.84], p=0.021; GS: 0.83 [0.37, 1.29], p<0.001) when compared to non-swollen non-tender joints.

Joints in RA patients have significantly higher temperature readings when ultrasound-detected joint inflammation is present. Swollen tender/non-tender joints exhibited a greater degree of ultrasound-detected joint inflammation than non-swollen non-tender joints, although their temperature readings were not significantly higher.