S5842 A Rare Presentation of Adult-Onset Still’s Disease Overlapping Autoimmune Hepatitis

Introduction: Adult-onset Still’s disease (AOSD) is a rare systemic inflammatory disorder with hepatic involvement in 60%–80% of cases. Liver injury is driven by cytokines (notably IL-18), macrophage/T-cell infiltration, and innate immune dysregulation. This contrasts with autoimmune hepatitis (AIH), which is characterized by T cell-mediated autoimmunity and adaptive immune dysfunction. Case Description/Methods: A 31-year-old Hispanic otherwise healthy woman presented in week 31 of pregnancy with flu-like symptoms and a generalized rash. Laboratory evaluation revealed a mixed pattern liver injury with an R-factor of 4.16, T bilirubin 8.6 mg/dL, and alkaline phosphatase (ALP) 829 U/L. international normalized ratio trended from 1.3 to 1.5. She was transferred to a quaternary center for multidisciplinary management after a spontaneous preterm delivery. Liver work up was negative for acute or chronic viral hepatitis. Notable labs included an antinuclear antibody of 1:80, IgG 2755 mg/dL, and weakly positive cytomegalovirus (CMV) 372 copies/ml. On postpartum transfer liver transaminases trend was; AST/ALT from 379/372 U/L to 351/341 U/L; ALP from 585 U/L to 608 U/L; T. bilirubin from 3.5 mg/dL to 3.7 mg/dL, but few days later she developed recurrent pruritus and fever. Liver chemistries worsened ALT/AST 462/468 U/L; ALP 1297 U/L. A liver biopsy demonstrated lobular inflammation with lymphocytes, histiocytes, plasma cells, neutrophils, and eosinophils, consistent with AIH. Prednisone and Ganciclovir were initiated with rising CMV PCR titers up to 1000 U/L. After transaminase improvement, she was discharged on a steroid taper, azathioprine and valganciclovir. Over the next several weeks, fevers, sporadic polyarthritis and posterior cervical lymphadenopathy recurred. At that time, liver chemistries were near normal, but inflammatory markers were elevated: ferritin 7,000 ng/mL and CRP 5.6 mg/dL. Rheumatology consultation and she was diagnosed with AOSD by Yamaguchi criteria. Anakinra (IL-1 receptor antagonist) was started with significant improvement. Discussion: Adult-onset Still’s disease (AOSD) is diagnosed clinically by Yamaguchi criteria with no specific immunological markers. It is a cytokine-driven inflammatory condition, while AIH involves adaptive immunity with autoantibodies and plasma cell-rich histology. This case illustrates a rare overlap between AOSD and AIH, underscoring the complexity of diagnosing and managing atypical hepatic manifestations. A multidisciplinary approach is crucial to address this diagnostic and therapeutic challenge.