Macrophage activation syndrome: I/II

Macrophage activation syndrome (MAS) is a potentially fatal systemic disorder which results from uncontrolled activation and proliferation of T cells and excessive activation of macrophages. It is a distinct clinicopathologic entity that occurs in different haemophagocytic syndromes (HSs). Primary haemophagocytic lymphohistiocytosis (HLH) is recognized to have an immunogenetic basis, but the secondary HS (also referred to as MAS) occurs in a number of autoimmune disorders including systemic onset juvenile idiopathic arthritis, SLE, adult onset Still's disease and other disorders. In first of the two part series, the aetiology, molecular pathogenesis and diagnostic features will be enunciated. The second part will deal with clinical features and management issues.