Influence of recent exercise and skin temperature on ultrasound Doppler measurements in patients with rheumatoid arthritis--an intervention study

Abstract

Use of ultrasound Doppler (USD) in diagnosing and treatment monitoring of patients with RA has increased considerably. Hyperaemia is an integral part of the inflammatory response, and the amount of USD activity in an inflamed synovium may therefore be used to quantify the inflammatory activity. It is unclear, however, whether the hyperaemia alone reflects the disease activity or may be influenced by other factors. Twenty-nine patients with RA underwent USD examination of the wrist before and immediately after three interventions. The interventions were carried out on three separate days. The interventions were (i) isometric exercise of the muscles of the hand and forearm, (ii) heating and (iii) cooling of the hand. The amount of Doppler in the wrist joint was quantified by measuring the percentage of colour in the synovium-the colour fraction (CF). The CF values estimated before and after each intervention were compared to see if any intervention affected the amount of Doppler in the synovium. The CF decreased significantly after cooling of the hand (P = 0.018 and <0.0001). Despite being highly significant, the numerical decrease in CF was only modest, 0.78-1.33 percentage points. The other interventions did not affect the CF significantly, with P-values of 0.65 and 0.59 in the heating intervention and 0.49 in the exercise intervention. Cooling of the hand should, if possible, be avoided before a USD examination of the wrist in patients with RA, because the amount of Doppler activity might be affected by low skin temperatures.