Background: Autoimmune pancreatitis (AIP) is a recently-recognized form of pancreatitis mimicking pancreatic cancer (PaC) but treatable with corticosteroid. There is one report of focal-type AIP in Thailand. Here we presented the first case report of diffuse-type AIP.
Case Report: A 76-year-old man presented with 10-day obstructive jaundice. Computed tomography (CT) showed obstructive jaundice from diffusely swollen pancreas, which had a characteristic capsule-like rim non-enhancement pattern of AIP. Serum immunoglobulin G4 (IgG4) was elevated of 468 mg/dL. Endoscopic ultrasound-guided fine needle aspiration demonstrated no PaC. Prednisolone 40 mg/day was started. Jaundice disappeared in 2 weeks and follow-up CT demonstrated normalization of swollen pancreas.
Conclusion: Diffuse-type AIP does exist in Thailand. Recognition of this condition is critical to avoid misdiagnosis of PaC or unnecessary surgery.

Keywords: Autoimmune pancreatitis, Diffuse type, IgG4