Hyperferritinemia Wins Again: Defining Macrophage Activation Syndrome in Pediatric Systemic Lupus Erythematosus.

Macrophage activation syndrome (MAS) is a potentially life-threatening condition of hyperinflammation that can be secondary to an underlying chronic rheumatic condition, commonly systemic juvenile idiopathic arthritis (sJIA) but also childhood-onset systemic lupus erythematosus (cSLE). MAS is characterized by excessive activation of T lymphocytes and macrophages that lead to overproduction of cytokines and results in cytopenia, liver dysfunction, and coagulopathy1.