A 55-year-old man with chronic pancreatitis presents with obstructive jaundice due to a pancreatic head mass. ERCP shows a 'double-duct sign.' Biopsy shows dense stromal fibrosis with bland ductal epithelium and no malignant features. IHC shows IgG4+ plasma cells >10/HPF. The MOST likely diagnosis is:

• A Type 1 autoimmune pancreatitis (IgG4-related disease, lymphoplasmacytic sclerosing pancreatitis) ✓
• B Pancreatic ductal adenocarcinoma
• C Mucinous cystic neoplasm with low-grade dysplasia
• D Groove pancreatitis (paraduodenal pancreatitis)

Explanation

Type 1 autoimmune pancreatitis (AIP) is an IgG4-related disease characterised histologically by lymphoplasmacytic infiltration with >10 IgG4+ plasma cells/HPF, storiform fibrosis, and obliterative phlebitis (LPSP pattern). It mimics pancreatic cancer clinically but responds dramatically to corticosteroids. Double-duct sign and pancreatic head mass are shared with pancreatic ductal adenocarcinoma, making biopsy and IgG4 serology critical.

Reference: Robbins & Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.