Irregular Narrowing of the Main Pancreatic Duct in Association With a Wall Thickening Is a Key Sign at Endoscopic Ultrasonography for the Diagnosis of Autoimmune Pancreatitis

OBJECTIVES: The aim of this study was to assess the accuracy of key signs identified at endoscopic ultrasonography in diagnosing an autoimmune pancreatitis (AIP). METHODS: Between January 2007 and December 2011, a retrospective case-control study was conducted in 177 patients with AIP (n = 30), pancreatic adenocarcinoma (n = 42), pancreatic neuroendocrine tumor (n = 21), alcoholic chronic pancreatitis (n = 32), and symptomatic common bile duct stones (n = 52). RESULTS: An irregular narrowing of the main pancreatic duct in association with a wall thickening was seen in 28 of 30 AIP, 1 of 42 pancreatic adenocarcinoma, 0 of 21 pancreatic neuroendocrine tumor, 0 of 32 alcoholic chronic pancreatitis, and 0 of 52 common bile duct stones (P < 0.05). Sensitivity, specificity, positive and negative predictive values, and overall diagnostic accuracy of this sign for the diagnosis of AIP were 93%, 99.3%, 96.3%, 98.6%, and 98.3%, respectively. In type 1 AIP, hyperechoic parietal thickening was more frequent (92.3% vs 33.3%, P < 0.05). In type 2 AIP, hypoechoic parietal thickening was more frequent (83.3% vs 23.1%, P < 0.05). CONCLUSIONS: An irregular narrowing of the main pancreatic duct in association with a wall thickening seen at endoscopic ultrasonography is accurate in diagnosing AIP. The type of echogenicity of the thickening is well correlated with the type of AIP.