Abstract
Adult-onset Still's disease (AOSD) is an immunological disorder that manifests with fever, evanescent rash, leukocytosis, and arthralgia. One of the most severe complications of AOSD is macrophage activation syndrome, a life-threatening complication characterized by hyperactivation of the immune system and multiorgan dysfunction. This case report describes a 24-year-old female who developed macrophage activation syndrome in the setting of AOSD. Initially, she developed heterogeneous and nonspecific symptoms of fever, pharyngitis, rash, lymphadenopathy, and migratory arthralgia after a trip to Mexico. Thus, the diagnosis and appropriate treatment were delayed. Although her symptoms were temporarily relieved with oral steroids, she worsened clinically. She developed a widespread rash, persistent fever, a very high ferritin level (29,972 ng/mL), and elevated liver enzymes with mild hepatosplenomegaly, raising concern for macrophage activation syndrome. After ruling out infections, she was diagnosed with AOSD, and treatment with intravenous steroids was started, resulting in clinical improvement. Macrophage activation syndrome is a rare but fatal complication. Early recognition, particularly with elevated ferritin, liver dysfunction, and thrombocytopenia, is very important. Early intervention with glucocorticoids and biologics like anakinra is crucial for improving outcomes. The patient is in remission with ongoing follow-up with rheumatology.