Pathophysiological Factors which Determine the Exercise Intolerance in Patients with Juvenile Dermatomyositis

Juvenile Dermatomyositis (JDM) is one of the idiopathic inflammatory myopathies in childhood. In this disease the immune system targets the microvasculature of the skeletal muscle and skin, leading to myopathy and a typical skin rash. During episodes of active disease patients experience a significant reduction in exercise tolerance which is not only related to loss in muscle mass. In this chapter we propose a model consisting of 5 pathways that could explain the reduced exercise tolerance in children with JDM. The five pathways are 1) the increased concentration of intramuscular cytokines, 2) the systemic inflammation process 3) the inflammation of the capillaries in the muscle 4) the result of hypo-activity and 5) the effect of glucocorticoid treatment on body mass gain and protein breakdown.