MATTERS ARISING EVect of intensive exercise on patients with active RA

The eVect of intensive exercise on disease activity in rheumatoid arthritis (RA) is an interesting one. Although we would not dispute that such exercise does indeed have a beneficial eVect on parameters of disease activity, we wish to propose an alternative hypothesis as to its mechanism. In particular, we would argue that the eVect of raised intraarticular pressure on synovial blood flow during exercise is not as the authors suggest. The intra-articular pressure in chronically inflamed joints undoubtedly rises during exercise, and exceeds capillary perfusion pressure within the synovium. 3 This pressure rise occurs in joints with and without eVusions. It is clearly diYcult to measure intra-articular pressure during dynamic exercise, but we would speculate that the pressure rises which occur during dynamic exercise are similar to those occurring during static exercise. The study that is quoted by the authors suggests that synovial blood flow increases during dynamic exercise such as walking and cycling and was only measured in joints with eVusions. We would argue that raised intra-articular pressure during any form of exercise not only compromises synovial blood flow, resulting in synovial hypoxia, but is the initiating step in reperfusion injury. Hypoxia-reperfusion injury is one of the mechanisms by which reactive oxygen species (ROS) are produced, including the highly toxic hydroxyl radical. Damage by such ROS to biomolecules and tissues within the rheumatoid joint is well documented. 8 Oxidative damage to fine nociceptor nerve endings within the synovium renders the joint relatively anaesthetic and perhaps allows the patient to exercise the joint more vigorously. We propose therefore that intensive exercise brings about an “auto-synovectomy”, eVectively reducing the amount of inflammation within the joint and thereby reducing the disease activity score.