Macrophage activation syndrome

Macrophage activation syndrome is a severe, potentially life-threatening complication that can arise in several chronic rheumatic diseases of childhood, occurring most often alongside systemic-onset juvenile idiopathic arthritis. It has also been described in association with systemic lupus erythematosus, Kawasaki disease, and adult-onset Still's disease, and is considered closely related to, and pathophysiologically very similar to, the reactive form of hemophagocytic lymphohistiocytosis. Its true incidence is unknown because its clinical presentation varies widely and many episodes likely go unrecognized.