Atypical Presentation of Adult-Onset Still's Disease with Predominant Hepatic Involvement and Monocytosis: A Case Report.

Introduction: Adult-Onset Still's Disease (AOSD) is a rare inflammatory disease. It usually causes high fevers, joint pain, a fleeting rash, and very high ferritin levels. The symptoms can mimic infections, autoimmune disorders, or cancers, so it can be hard to diagnose. Liver involvement is common but usually mild. Severe hepatitis is rare. Case Presentation: We report a 24-year-old woman who had 3 weeks of daily high fevers, a temporary salmon-pink rash, sore throat, muscle pain, and joint pain. Her blood tests showed high white blood cells with mostly neutrophils, persistent monocytosis, severely elevated liver enzymes, and very high ferritin. Tests ruled out infections, autoimmune diseases, and cancers. She met criteria for AOSD, and her glycosylated ferritin was low. The patient responded rapidly to intravenous methylprednisolone, but relapsed with polyarthritis upon tapering, which resolved completely within 48 hours of initiating anakinra. Discussion: This case highlights the diagnostic challenges of AOSD presenting predominantly with hepatic involvement and atypical laboratory features such as persistent monocytosis. Recognition of extreme hyperferritinemia as a diagnostic clue can prevent delays in diagnosis. The dramatic response to IL-1 blockade underscores cytokine dysregulation as a central pathogenic mechanism. Conclusion: Clinicians should consider AOSD in patients with febrile hepatitis and extreme hyperferritinemia. Early initiation of biologic therapy targeting IL-1 can achieve rapid remission, improve quality of life, and prevent complication.