Mass Forming Autoimmune Pancreatitis, Misdiagnosed as Pancreatic Cancer: Case Report

Autoimmune pancreatitis is characterized by infiltration of the pancreas parenchyma by immunoglobulin G4 (IgG4)-positive plasma cells, chronic inflammation, and fibrosis. It can affect the entire body depending on the subtype. Distinguishing mass-forming type autoimmune pancreatitis from pancreatic cancer can often be challenging. A 60-year-old male presented to our outpatient clinic with abdominal discomfort. Computed tomography revealed a 4.8 cm mass in the pancreatic head obstructing the common bile duct. Endoscopic ultrasound-guided fine needle biopsy and endoscopic retrograde cholangiopancreatography with biliary drainage were performed. Pathological examination revealed no malignant cells, but more than 20 IgG4-positive cells were observed. Following two weeks of steroid treatment, the patient’s symptoms improved, and follow-up imaging showed a reduction in the size of the pancreatic head mass. Herein, we report a case of mass-forming autoimmune pancreatitis initially misdiagnosed as pancreatic cancer.