Endoscopic Ultrasound Features of Autoimmune Pancreatitis: A Unique Chronic Pancreatitis Pattern

Abstract

Background: Autoimmune pancreatitis (AIP) is a special form of chronic pancreatitis (CP) with dramatic response to corticosteroid therapy. This study focused on the endoscopic ultrasound (EUS) features of newly diagnosed AIP. Methods: This retrospective single-center study included 286 patients of newly diagnosed AIP following the HISORt criteria, and all EUS was accomplished before corticosteroid therapy. The Rosemont criteria was applied to all the AIP patients not only for descriptions of CP features but also for diagnosis of CP. We also compared the EUS findings and the diagnosis of CP between the diffuse and focal types of AIP cases. Findings: For parenchymal changes of CP, hyperechoic foci, cystic lesion, parenchymal calcification, lobularity with/without honeycombing were all comparable between both groups, while hyperechoic striation was significantly more in the focal group (P = 0·02); for main pancreatic duct (MPD) changes of CP, MPD stones, diffuse irregularity and hyperechoic ductal margin were comparable in both groups, while MPD dilation was significantly more in the focal group (P = 0·03). A unique EUS characteristic of AIP parenchymal changes was noticed that we coined as the snowflake sign which was seen in a large number of AIP case (88·1%). The diagnosis of CP according to the Rosemont criteria was also comparable in both groups (P = 0·54). Interpretation: This study demonstrated that the newly diagnosed AIP patients showed unique CP EUS features with the snowflake sign seen in a large number of AIP cases; the diagnosis of CP according to the Rosemont criteria in the diffuse type and focal type AIP cases was comparable. Funding Statement: The authors stated: None. Declaration of Interests: The authors declare no competing interests. Ethics Approval Statement: The study was approved by the Ethics Committee of our institution, and written consent was obtained in all patients.