Hidden in plain sight: macrophage activation syndrome complicating Adult Onset Still's Disease.

Hemophagocytic Lymphystiocytosis is a rare and fatal complication of rheumatic diseases, particularly Adult Onset Still's Disease (AOSD). It may be precipitated with immunosuppressive drugs and with viral and bacterial infections. A diagnosis depends on a high index of suspicion associated to certain clinical manifestations (fever, rash, Splemomegaly, any cytology blood dyscrasia, hipertrigliceridemia, hiperfibrinogenemia, and others), as well as pathologic evidence of hemophagocitosis from bone marrow biopsy or tissue samples of affected organs. Therapy consists of high dose corticosteroids and immunosuppressive drugs. We present a 42 year old woman with AOSD in remission who developed HLH in spite of receiving therapy with high dose steroids and immunosuppressive drugs. She had 2 negative bone marrow aspirates. Evidence of Hemophagocytosis was detected in both bone marrow biopsies. Timely evaluation and recognition of the signs and symptoms of HLH is crucial for the prompt management and a decrease in the mortality associated with this disease.