Macrophage Activation Syndrome.

Macrophage Activation Syndrome (MAS) occurs as a severe life-threatening complication of several chronic rheumatic diseases. It is more frequent with systemic onset juvenile arthritis and adult onset Still's disease.1 It can be primary, infection related, malignancy associated or autoimmune3. We report a case of Macrophage Activation Syndrome presenting as pyrexia of unknown origin (PUO) and pancytopenia in the absence of any known triggering factor.