Systemic Juvenile Idiopathic Arthritis Complicated by Macrophage Activation Syndrome.

Systemic juvenile idiopathic arthritis (sJIA) is characterized by a large range of extra-articular manifestations in addition to joint inflammation. The child with sJIA usually presents with a spiking fever pattern, evanescent rash, and arthralgias/arthritis. Other features often present are lymphadenopathy, hepatosplenomegaly, and polyserositis. The systemic manifestations are frequently more prominent and severe than the arthritis. Laboratory studies reflect systemic inflammation with significant anemia, and elevation of acute phase reactants, platelets, and white blood cell count. Ferritin level is often strikingly high. The treatment of sJIA has evolved over the past decade with the improved understanding of the role of specific inflammatory cytokines in this disease. The medications employed to treat sJIA directly inhibit the actions of these cytokines. A major cause of morbidity and mortality of children with sJIA is the development of macrophage activation syndrome, which can cause unremitting fevers, pancytopenia, coagulopathy, and hepatic dysfunction.