Autoimmune Hepatitis Mimicking Pancreatico-Biliary Malignancy.

A man in his 80s presented with a one-week history of jaundice, abdominal pain, low-grade fever, pruritus, and anorexia. Biochemistry showed a hepatocellular pattern of liver injury, with aspartate aminotransferase of 867 U/L and alanine aminotransferase of 702 U/L, alongside conjugated hyperbilirubinemia and a prolonged international normalized ratio. Contrast-enhanced computed tomography of the abdomen showed a bulky pancreatic head and uncinate process with mild common bile duct dilatation and no discrete mass, alongside a markedly elevated CA 19-9 of 225 U/mL, which together raised initial concern for pancreatico-biliary malignancy. A comprehensive viral hepatitis panel, including hepatitis A, B, C, and E, and thyroid function testing were unremarkable. Further workup revealed a strongly positive antinuclear antibody at high titer and an elevated total immunoglobulin G. A clinical diagnosis of autoimmune hepatitis was made using simplified international diagnostic criteria; liver biopsy was offered but declined by the patient due to his advanced age and practical constraints. Treatment with corticosteroids and azathioprine led to complete biochemical normalization over several weeks, with sustained improvement on maintenance therapy. This case demonstrates that autoimmune hepatitis can closely mimic pancreatico-biliary malignancy on cross-sectional imaging and tumor markers in an older patient, and highlights the diagnostic value of autoimmune serology and immunoglobulin G levels in avoiding unnecessary invasive oncological investigation.