dawnmedDawnMed Journal of Medical ScienceISVolume 2, Issue 2MultidisciplinaryEnglish2026NNY20260624RheumatologyAdult-Onset Still's Disease with Macrophage Activation Syndrome Mimicking Septic Shock During Clostridioides difficile Colitis: A Case ReportEnglishY1016Batool SalehBedaiwi¹EnglishNGharam AbdulazizAlahmadi²EnglishYNorah SaeedAlqahtani³EnglishYReem ZayedAlshalan⁴EnglishYAbdulaziz FahadSamandar⁵EnglishYMohammed HadramAldossary⁶EnglishYZahraAlmaghrabi⁷EnglishYHyderMirghani¹EnglishY10.64039/djms.2026.2202Background: Adult-onset Still's disease (AOSD) is a rare systemic autoinflammatory disorder characterized by fever, arthritis, and hyperferritinemia. It may be complicated by macrophage activation syndrome (MAS), a life-threatening hyperinflammatory state that can mimic severe sepsis, especially in the presence of concurrent infection. Early recognition is critical but often challenging.Case Presentation: We report a 22-year-old previously healthy female who presented with a five-month history of quotidian fever, significant weight loss, and inflammatory polyarthritis. Her clinical course was complicated by septic shock in the setting of confirmed Clostridioides difficile colitis. Extensive workup excluded infectious, malignant, and autoimmune etiologies. Laboratory findings revealed extreme hyperferritinemia (peaking >33,511 ng/mL), progressive cytopenias, hypertriglyceridemia, hypofibrinogenemia, and elevated soluble IL-2 receptor levels, consistent with MAS/secondary hemophagocytic lymphohistiocytosis. The diagnosis of AOSD was established using Yamaguchi criteria. Despite initial management for sepsis, persistent fevers and worsening laboratory parameters prompted escalation to pulse-dose corticosteroids, anakinra, and intravenous immunoglobulin. The patient demonstrated significant clinical and biochemical improvement, was transitioned to tocilizumab for maintenance therapy, and was discharged in stable condition.Conclusion: This case highlights the diagnostic complexity of AOSD complicated by MAS in the setting of concurrent infection. Extreme hyperferritinemia, evolving cytopenias, and lack of response to antimicrobial therapy should prompt consideration of MAS. Early recognition and timely initiation of immunomodulatory therapy are crucial for improving outcomes in this potentially fatal condition.EnglishAdult-Onset Still's Disease, Macrophage Activation Syndrome;, Hemophagocytic Lymphohistiocytosis;, Clostridioides difficile Colitis, Anakinra Tocilizumab, Cytokine Storm, Fever of Unknown Origin.https://dawnmed.com.sa/abstract?id=15References16191. Gerfaud-Valentin M, Jamilloux Y, Iwaz J, Sand;egrave;ve P. Adult-onset Stilland;#39;s disease. Autoimmun Rev. 2014;13(7):708and;ndash;22.2. Efthimiou P, Kadavath S, Mehta B. 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