Iván López-Méndez, Unidad de Endoscopia, Fundación Clínica Médica Sur, México City, Mexico
Claudia Maya-Salazar, Department of Internal Medicine. Fundación Clínica Médica Sur, México City, Mexico

Type 1 autoimmune pancreatitis is a fibroinflammatory condition within the immunoglobulin G4 (IgG4)-related disease spectrum, characterized by lymphoplasmacytic infiltration, storiform fibrosis, and elevated serum IgG4 levels. It represents a significant diagnostic challenge due to its frequent radiologic and clinical overlap with pancreaticobiliary malignancies. We describe the case of a 70-year-old male who developed obstructive cholestasis after endoscopic treatment for choledocholithiasis. Multimodal imaging, including endoscopic retrograde cholangiopancreatography, magnetic resonance cholangiopancreatography, and positron emission tomography-computed tomography, showed biliary strictures, a pancreatic head mass, and metabolically active lymphadenopathy. Histopathologic confirmation through endoscopic ultrasound-guided biopsy, along with serologic results, established the diagnosis. Early corticosteroid therapy resulted in significant biochemical and radiologic improvement.

Keywords: Autoimmune pancreatitis. Immunoglobulin G4. Endoscopic ultrasound.