Chapter 3 Systemic Juvenile Idiopathic Arthritis

The diagnosis of systemic juvenile idiopathic arthritis (sJIA) requires the rigorous exclusion of a broad range of conditions, particularly infections and malignancies, and in the younger infants, the autoinflammatory syndromes. The clinician should be vigilant for both the common and less common systemic manifestations of the disease. Macrophage activation syndrome (MAS) is a potentially fatal complication that requires prompt diagnosis and treatment. New classification criteria for MAS associated with sJIA have been proposed. The identification of clinical, laboratory, and more recently genetic predictors of disease course, outcome, and response to treatment may help to identify patients who may benefit from early aggressive treatment. Patients with sJIA generally do not respond as well as other subtypes of JIA to standard therapies. An improved understanding of the roles of interleukin (IL)-1 and IL-6 in the pathogenesis of sJIA has resulted in new and highly effective therapies aimed at neutralizing the actions of these cytokines.