# Utility of Infrared Thermography in Assessing Synovitis in Rheumatoid Arthritis: An Observational Study

## TL;DR

This study shows that infrared thermography can detect joint inflammation in rheumatoid arthritis and may help identify hidden inflammation in patients.

## Contribution

The study introduces infrared thermography as a non-invasive, cost-effective method for assessing synovitis in rheumatoid arthritis.

## Key findings

- IRT detected higher joint temperatures in RA patients compared to controls across 28 joints.
- IRT showed moderate correlation with DAS28-ESR and identified subclinical synovitis in patients in remission.

## Abstract

Introduction

There is an unmet need for an objective, cost-effective, and user-friendly tool to assess disease activity in rheumatoid arthritis (RA). This pilot study explores the utility of infrared thermography (IRT) in evaluating temperature differences between diseased and normal joints, and its correlation with the Disease Activity Score in 28 joints using Erythrocyte Sedimentation Rate (DAS28-ESR).

Methods

We recruited 50 RA patients (90% female subjects, mean age 47.7 years, mean disease duration 6.2 years) and 50 age- and sex-matched healthy controls. Clinical disease activity was assessed using DAS28-ESR, and IRT was performed across 28 joints, with mean joint temperature (T mean) compared between groups and correlated with disease activity.

Results

Of the 1400 diseased joints assessed, 126 were swollen and 297 were tender, with 21 patients (42%) showing high disease activity (mean DAS28-ESR 4.59). T mean was significantly higher in patients with RA than controls across all 28 joints (p<0.05), with a moderate correlation to DAS28-ESR (r=0.646). Receiver Operating Characteristic (ROC) analysis yielded an area under the curve (AUC) of 0.84, with 83% sensitivity and 73% specificity at a T mean cut-off of 33.45°C. Thermography detected tenosynovitis in two patients, subclinical synovitis in eight patients in clinical remission, and differentiated active from damaged joints in 10 patients.

Conclusion

IRT is a promising, non-invasive tool for detecting joint inflammation in RA, with the potential to enhance everyday clinical practice by identifying subclinical synovitis, tenosynovitis, and active joints, particularly in resource-limited settings.