Macrophage activation syndrome following initiation of etanercept in a child with systemic onset juvenile rheumatoid arthritis.

Systemic onset juvenile rheumatoid arthritis (JRA) accounts for 10-15% of all JRA. Macrophage activation syndrome (MAS), which can also be considered as secondary hemophagocytic lymphohistiocytosis, is a potentially life-threatening complication of systemic onset JRA. We describe a child with systemic onset JRA who developed MAS after initiation of etanercept therapy.