[Macrophage activation syndrome in a patient with systemic juvenile idiopathic arthritis].

Machrophage activation syndrome (MAS) is a rare and potentially fatal disease, commonly associated with chronic rheumatic diseases, mainly juvenile idiopathic arthritis. It is included in the group of secondary forms of haemophagocytic syndrome, and other causes are lymphoproliferative diseases and infections. Its most important clinical and laboratorial manifestations are non-remitting fever, splenomegaly, bleeding, impairment of liver function, cytopenias, hypoalbuminemia, hypertriglyceridemia, hypofibrinogenemia and hyperferritinemia.