Autoimmune pancreatitis masquerading as a pancreatic neoplasm: A case report

Acute pancreatitis is common with potential serious sequela; representing the 5th leading cause of in-hospital mortality. Autoimmune pancreatitis (AIP) is rare, separated into type 1 and type 2 AIP. Type 1 AIP is associated with systemic immunoglobulin G4 related disease (IgG4-RD) whereas type 2 AIP is localized disease characterized by neutrophilic infiltrate. Both types of AIP can cause recurrent acute pancreatitis and chronic inflammation. On imaging, AIP can present as a focal pancreatic mass mimicking pancreatic cancer. Given the potential for misdiagnosis and unnecessary surgery, it is important for clinicians to recognize AIP in patients presenting with pancreatic masses and recurrent pancreatitis.

A 51-year-old female with a history of hyperlipidemia, Grave disease s/p thyroidectomy and recurrent acute pancreatitis s/p cholecystectomy presented with 3 to 4 days of epigastric pain radiating to the back with nausea, vomiting and diarrhea.

Labs showed elevated lipase (629 U/L) and leukocytosis. CT Abdomen and Pelvis showed pancreatitis with peri/pancreatic edema and a 1.4 cm pancreatic head hypoattenuating focus. Magnetic resonance imaging with and without contrast with magnetic resonance cholangiopancreatography (MRCP) revealed a 3.9 cm mass concerning for adenocarcinoma. Serum carbohydrate antigen 19-9 (CA-19-9) was elevated (186 U/mL), and carcinoembryonic antigen was normal. Endoscopic ultrasound showed a pancreatic head 3.4 cm heterogenous mass-like lesion. Histopathology showed neutrophilic infiltrates, microabscesses and fibrosis without malignancy consistent with AIP type 2. Serum immunoglobulin G4 was normal (20.6 mg/dL).

The patient was started on a prednisone taper of 40 mg daily.

Her symptoms improved. Two weeks later, lipase decreased to 77 U/L and CA-19-9 was 30 U/L. Repeat MRCP showed improvement.

This case highlights the importance of AIP as a rare but critical differential for recurrent pancreatitis and pancreatic masses. Recognizing this entity is essential to increase provider familiarity with its clinical presentation when evaluating similar patients. Awareness of AIP can lead to earlier diagnosis and treatment, preventing unnecessary oncologic workups or surgery. This can reduce the risk of complications, recurrences, and lifetime cancer risk, improving patient outcomes.