Adult-Onset Still's Disease(AOSD) With Features Suggestive of Macrophages Activation Syndrome in Young Female: A Rare Case Report From Nepal.

Adult-onset Still's disease (AOSD) is a rare, multisystem autoinflammatory disorder characterized by a classic triad of fever, evanescent rash, and arthritis with diagnostic challenges. We present a case of a previously healthy 22-year-old Nepalese female presented with a 1.5-month history of progressive bilateral lower limb edema and a 13-day history of high-grade quotidian fever. Clinical evolution included a classic salmon-pink, evanescent maculopapular rash exhibiting the Koebner phenomenon, arthralgias, sore throat, posterior cervical lymphadenopathy, and hepatosplenomegaly. During hospitalization, she abruptly deteriorated with generalized anasarca, oliguria, tachypnea, and hypoxia, necessitating intensive care unit (ICU) admission for suspected systemic capillary leak syndrome and evolving macrophage activation syndrome (MAS). Laboratory investigations revealed leukocytosis, anemia, an elevated C-reactive protein paradoxically with a normal erythrocyte sedimentation rate, hyperferritinemia, transaminitis, and a positive direct Coombs test. Autoantibodies were negative with an unremarkable infectious workup. Management in the ICU included supportive care and broad-spectrum antibiotics. Following the confirmation of AOSD, she received intravenous methylprednisolone pulse therapy, leading to dramatic clinical and biochemical improvement, including a significant decline in ferritin. She was transitioned to oral prednisolone and stabilized for discharge with a plan to initiate methotrexate as a steroid-sparing agent. This case underscores the diagnostic complexity and potential severity of AOSD, mimicking sepsis and systemic inflammatory complications. The atypical presentation with predominant peripheral edema preceding fever and the laboratory finding of elevated CRP with normal ESR are noteworthy. Early recognition, prompt initiation of immunosuppressive therapy, and vigilant monitoring for MAS are crucial to reducing morbidity and mortality in this challenging condition.