Adult-onset Still's disease complicated by macrophage activation syndrome.

Key Clinical Message: Young patients with persistent rash and fevers despite antibiotic treatment should be evaluated for non-infectious etiologies. In our patient's case, these findings led to a diagnosis of MAS, which ultimately affected how she was managed. Abstract: Adult-onset Still's disease (AOSD) is a rare, often difficult to diagnose autoimmune disease that typically presents as a rash, unresolving fevers and joint pains capable of mimicking a number of autoimmune diseases. Here, we present the case of a young postpartum woman whose clinical presentation, which included a pruritic maculopapular rash that evolved to include a flagellate component, and serological studies, chief among them cytopenias and a Ferritin >15,000 nm/mL) allowed us to make an early diagnosis of AOSD complicated by macrophage activation syndrome. We discuss the treatment for AOSD complicated by MAS with Hydrocortisone and Anakinra, the final discharge regimen prescribed for our patient, and report on her state 3 months post-hospitalization, which was favorable. Our case is unique because we ultimately believe that pregnancy itself triggered her ASOD, because of how the quality of the flagellate component of her rash allowed us to narrow the differential diagnosis, and because of how the significant cytopenias and significant liver dysfunction alerted us to the possibility of MAS.