Coexisting autoimmune pancreatitis and pancreatic adenocarcinoma: Diagnostic challenges and case insights.

The coexistence of autoimmune pancreatitis and pancreatic adenocarcinoma represents a rare but clinically significant diagnostic dilemma. Elevated IgG4 levels and imaging features suggestive of autoimmune pancreatitis may mask an underlying malignancy, leading to potential delays in definitive diagnosis and treatment. This overlap highlights the limitations of relying solely on clinical, serologic, and radiologic findings in the absence of histopathologic confirmation. We report a case of pancreatic ductal adenocarcinoma occurring in the setting of suspected autoimmune pancreatitis (AIP), highlighting the diagnostic challenge of overlapping imaging and biochemical features and the potential coexistence of both entities. A 51-year-old patient presented with progressive jaundice and unintentional weight loss. Laboratory evaluation revealed cholestasis, elevated tumor markers including CA 19-9, and markedly increased serum IgG4 levels (340 mg/dL; reference range 4.8-105 mg/dL). Contrast-enhanced computed tomography revealed a diffusely enlarged, sausage-shaped pancreas, associated with a focal hypoattenuating lesion in the uncinate process, regional lymphadenopathy, and peritoneal nodularity with ascites. Assessment of the pancreatic ductal system using gadolinium-enhanced MRI and MRCP demonstrated irregular narrowing of the main pancreatic duct without significant upstream dilatation. Histopathologic examination confirmed pancreatic ductal adenocarcinoma. This case emphasizes that pancreatic malignancy may coexist with AIP, and should not be excluded despite characteristic imaging and biochemical findings.