S3644 A Tangled Tale: Type 2 Autoimmune Pancreatitis With a Sclerosing Twist

Introduction: Autoimmune pancreatitis (AIP) is classified into 2 types: type 1, which is associated with elevated immunoglobulin subclass 4 (IgG4) levels, and the rarer type 2, which typically does not have elevated IgG4 and is often linked with inflammatory bowel disease (IBD). Obstructive jaundice is the most common presentation. Secondary sclerosing cholangitis (SSC) refers to a group of cholestatic liver diseases characterized by bile duct inflammation and fibrosis, leading to stricture formation. We present a case of AIP2 complicated by SSC, highlighting the associated diagnostic challenges. Case Description/Methods: A 39-year-old woman with Crohn's disease on infliximab and methotrexate presented with 1 week of abdominal pain, pruritis, and jaundice. Laboratory results showed a normal WBC, mild lipase elevation (66 U/L), with elevated AST (426 U/L), ALT (408 U/L), and ALP (822 U/L). Abdominal ultrasound revealed increased liver echogenicity without ductal dilation. Endoscopic ultrasound (EUS) revealed a hyperechoic, edematous pancreatic head concerning for AIP, along with common bile duct dilation. Pathology demonstrated reactive glandular cells. Endoscopic retrograde cholangiopancreatography (ERCP) identified biliary strictures, requiring sphincterotomy and stent placement, suspicious for SSC. IgG4 was low (3.3 mg/dl), and anti-mitochondrial antibodies were within normal limits. One month later, EUS showed hyperechoic strands throughout the pancreas, and biopsy revealed chronic inflammation with occasional plasma cells. She was treated with prednisone, resulting in clinical improvement. However, she was unable to tolerate tapering and required continued immunosuppression with mycophenolate. She developed type 3c diabetes and progressive biliary strictures. Discussion: The patient’s low IgG4, pancreatic head fullness on imaging, positive response to immunosuppression, IBD association, and recurrent biliary strictures were highly suggestive of AIP2 complicated by SSC, despite inconclusive biopsy findings. Although granulocytic epithelial lesions are diagnostic of AIP2, they may have been missed due to sampling error. Early recognition is critical to prevent stricture formation and complications such as type 3c diabetes, which results from pancreatic exocrine insufficiency. This case underscores the importance of considering AIP2 in patients presenting with obstructive jaundice, particularly when there is a favorable response to steroids.