Steroid-resistant Relapse of Autoimmune Pancreatitis with Marked Main Pancreatic Duct Dilatation Mimicking Multifocal Pancreatic Cancer.

A 67-year-old man with type 1 autoimmune pancreatitis (AIP) and IgG4-related sclerosing cholangitis experienced a relapse, while presenting with pancreatic head swelling and distal bile duct stenosis. Despite an increase in the prednisolone dosage (from 7.5 to 20 mg/day), the disease worsened. A significant dilatation of the main pancreatic duct (8 mm) and new stenosis of the pancreatic tail duct were observed. Malignancy was ruled out by repeated endoscopic ultrasound-guided fine-needle aspiration biopsies. A further escalation of the prednisolone dose to 40 mg/day led to clinical and radiological improvements. This case underscores the difficulty in distinguishing a steroid-resistant AIP relapse from pancreatic cancer, and the importance of ruling out malignancy before intensifying immunosuppressive therapy.