Macrophage activation syndrome, an important differential diagnosis for septic shock.

Macrophage activation syndrome (MAS) is a rare and life threatening complication of rheumatic diseases. It is seen most frequently in association with systemic onset juvenile idiopathic arthritis and less commonly in other rheumatic diseases of childhood including systemic lupus erythematosus. Recognition of MAS in patients with rheumatic diseases is often challenging as it may mimic the clinical features of the underlying disease. Sometimes MAS can be the mode of initial presentation adding to the diagnostic complexity. We describe two cases of MAS in association with systemic onset juvenile idiopathic arthritis who presented with a clinical picture suggestive of septic shock. The Internal Review Board at Shands Children's Hospital and the University of Florida waived the need for approval for these case reports.