Thermal imaging in rheumatoid arthritis knee joints and its correlation with power Doppler ultrasound.

Background: Power Doppler ultrasound (PDUS) is an established non-invasive modalities for quantification of inflammation, which has a bearing on the assessment of disease activity in rheumatoid arthritis (RA). However, PDUS has several disadvantages including cost of equipment, steep learning curve and inter-observer variability. Thermal imaging has emerged as a simple, powerful tool for mapping the heat distribution pattern and has the potential to document and quantify disease activity in RA. The objective was to study the thermal imaging pattern of inflamed knee joints in cases of RA and its correlation with PDUS.

Methods: This pilot case-control study was carried out at the rheumatology centre in India including 100 subjects (50 controls and 50 RA patients). All participants underwent thermal imaging and PDUS for the knee joints. The mean temperatures in area of interest in knee, thigh and knee-thigh differential were analysed in comparison with PDUS findings.

Results: RA subjects had significantly higher mean knee temperature and mean knee-thigh temperature differential compared with controls (p value < 0.00001). PDUS documented inflammation strongly correlated with knee-thigh temperature differential.

Conclusion: There was a statistically significant difference in mean knee temperature as well as mean knee-thigh temperature differential of inflamed versus control knees. Thermal imaging has the potential to become simple, objective, cost-effective and reliable tool for diagnosis and assessment of disease activity in inflammatory arthritis.