Assessment of Disease Activity by Infrared Thermography in Patients with Rheumatoid Arthritis: A Comparative Cross-Sectional Study of Thermographic, Clinical and Ultrasound Assessments

Abstract

OBJECTIVES: To compare RA activity evaluation by thermal imaging with a camera adjustable to cellphones, standard clinical examination and ultrasound.MATERIALS AND METHODS: Monocentric study with 3 independent evaluations of RA activity: 1) tender (TJC) and swollen joints count (SJC) of wrists, MCP and PIP; 2) Ultrasound (US) examination with mode B and Power Doppler (PDUS); 3) thermographic assessment using infrared thermal cellphone camera FLIR One®. Thermal images analysis with (a) software detecting 10 regions of interest (ROI) corresponding to the studied joints and (b) by color reading (arthritis yes/no). For each ROI, temperature difference measurement “ΔT-joint” (ΔTj) compared to the ipsilateral forearm (reference area) and comparison of ΔTj to a) TJC and SJC; b) US synovitis in B mode or c) PDUS grade (0,1,2,3); d) synovitis in visual detection on thermographic image. T-tests and ANOVA were performed.RESULTS: 53 patients (43 women) with a mean (SD) age of 61.6 (12.3) years, totaling 921 examined joints. Mean disease duration was 17.6 (11.1) years. RA status was 81% ACPA+, 58% erosive, mean DAS28 score was 4.0 (1.6).Mean ΔTj was higher in tender (p<0.001), swollen (p=0.066) joints and in US synovitis in B mode (p=0.021). Mean ΔTj was not associated with PDUS category (p-ANOVA=0.072). Synovitis detected with thermal image reading was associated with PDUS grade 3 (p<0.001). CONCLUSION: Our results did not show the ability of thermal imaging to assess RA activity in small joints. However, our results are encouraging as temperature variation were observed in inflammatory joints.