Abstract
ObjectiveMicrowave Radiometry is a non-invasive method which determines within seconds the in vivo temperature of internal tissues at a depth of 3–7 cm with an accuracy of ±0.2°C. In this proof-of-concept study, we tested the hypothesis that, in absence of relevant clinical signs, increased local temperature detected by microwave radiometry reflects subclinical synovial inflammation, using ultrasound as reference method.MethodsKnees of healthy controls, subjects with recent knee trauma and symptom-free patients with rheumatoid arthritis (RA) or osteoarthritis were examined by placing the microwave radiometry sensor, a) at the upper one third of the anterior surface of the thigh (control-point), and b) over the suprapatellar recess. Ultrasound was performed immediately after and the possible presence of fluid and/or synovitis was correlated with microwave radiometry findings.ResultsIn 30 healthy and 10 injured knees the temperature was always lower than thigh (32.3±1.1 and 31.8±1.4 versus 34.1±0.9 and 33.6±1.2°C with a difference (ΔΤ) of −1.8±0.2 and −1.9±0.4°C respectively). Of 40 RA and 20 osteoarthritis knees examined, ultrasound findings indicative of subclinical inflammation (fluid effusion and/or Doppler signal) were found in 24 and 12, respectively, in which the temperature was higher than healthy knees and ΔΤ was lower (−0.9±0.7 in RA and −1.0±0.5 in osteoarthritis versus −1.8±0.2°C, p<0.001). The 5 RA knees with power Doppler findings indicative of grade 2 inflammation had a ΔΤ 3 times lower compared to healthy (−0.6±0.6, p = 0.007), whereas the 9 RA and the 7 osteoarthritis knees with additionally fluid effusion, had even lower ΔΤ (−0.4±0.7, p<0.001).ConclusionUsing a safe, rapid and easy-to-perform method, such as microwave radiometry, thermal changes within the knee joint may reflect non-clinically apparent joint inflammation. Refinement of this method, including production of sensors for small joints, could result to the development of the ideal objective tool to detect subclinical synovitis in clinical practice.
Highlights
Rheumatoid arthritis, the most common systemic autoimmune disease, is characterised by the chronic inflammation in multiple joints which leads to cartilage damage and bone erosion
57.2610.5 years) or OA (n = 10, aged 61.966.5 years) who fulfilled the respective American College of Rheumatology classification criteria were examined. In addition to their willingness to participate in the study, the only inclusion criterion was the absence of pain and any clinical sign of knee joint inflammation in physical examination performed by a rheumatologist
To further elaborate the hypothesis that increased local temperature detected by Microwave radiometry (MR) reflects subclinical synovial inflammation we examined control subjects who had non-inflammatory unilateral knee pathology, either meniscal tear or cruciate ligament injury confirmed by magnetic resonance imaging (MRI), in the past 3 months (n = 10, aged 45.666.5) All underwent evaluation by MR, followed immediately by knee ultrasound by an experienced operator who was blinded to MR measurements
Summary
Rheumatoid arthritis, the most common systemic autoimmune disease, is characterised by the chronic inflammation in multiple joints which leads to cartilage damage and bone erosion. Synovitis has traditionally been assessed by means of clinical and laboratory parameters suggestive of local inflammation Modern imaging techniques, such as musculoskeletal ultrasound and magnetic resonance imaging (MRI), are playing an increasingly important role in the evaluation and monitoring of arthritis activity [3,4]. MRI involves substantial time and cost, exposure to contrast agents, and is not widely available for routine clinical use in many countries. Both ultrasound and MRI can detect subclinical synovial inflammation’s presence which may explain the structural progression reported in RA patients who satisfy conventional criteria of disease remission [5]
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