What is the most feared life threatening complication seen in Systemic Juvenile Idiopathic Arthritis?
Macrophage activation syndrome (MAS). MAS is a form of hemophagocytic lymphohistiocytosis that occurs secondary to a rheumatologic condition. MAS occurs in up to 10% of sJIA patients. The most common manifestations are persistently high fevers, hepatosplenomegaly, lymphadenopathy, severe cytopenias, liver dysfunction, hypertriglyceridemia, and central nervous system symptoms including seizures and coma, and coagulopathy (elevated prothrombin time and partial thromboplastin time as a result of low fibrinogen). If untreated, MAS can lead to multiorgan failure and eventually death.
MAS should be considered in any sJIA patient who develops a precipitous decrease in ESR (resulting from low fibrinogen), decrease in leukocyte and platelet counts, liver dysfunction, and hypertriglyceridemia. Ferritin level is usually >3000 to 10,000 ng/mL and fibrin degradation products are increased. Soluble IL-2 receptor alpha (sCD25) is elevated and correlates closely with disease activity. Biopsies show macrophages (CD163+) exhibiting hemophagocytosis in the bone marrow, lymph nodes, or liver. The cause of MAS is not known; however it is commonly associated with infectious triggers or flare of the underlying rheumatologic condition. Common infectious triggers include Epstein–Barr virus.