Macrophage Activation Syndrome Versus Hemophagocytic Lymphohistiocytosis: A Diagnostic Dilemma in a Patient With Still's Disease and Epstein-Barr Virus Viremia.

Macrophage activation syndrome (MAS) and hemophagocytic lymphohistiocytosis (HLH) are two overlapping, potentially fatal syndromes classified by disorganization and malfunction of the immune system that results in wide spread inflammation and end-organ damage. We present the case of a 22-year-old female with both underlying adult-onset still's disease and active Epstein-Barr virus (EVB) viremia who presented with criteria for MAS/HLH. She ultimately improved on an immunosuppressive regimen, and during follow-up was also found to be heterozygote carrier for a known genetic mutation that has been associated with "primary" HLH. This case thus highlights the clinical spectrum of HLH/MAS, the different treatment approaches, and the new investigations into the relationship between primary and secondary HLH.