Macrophage Activation Syndrome: Not Just for Rheumatologists Anymore

Macrophage activation syndrome (MAS) is a term that was originally used to describe a hyperinflammatory syndrome that developed in some patients with rheumatologic diseases. It is now clear that MAS and hemophagocytic lymphohistiocytosis (HLH) are defined by the same core pattern of clinical symptoms and share an underlying pathophysiology of impaired cytolytic activity and IFNγ-driven cytokine storm. Given that these disorders are highly related, lessons learned from the management of MAS can provide insights into effective approaches for HLH, particularly the strategy to employ anti-cytokine therapies early in the disease course.