Mechanisms of lower bile duct stricture in autoimmune pancreatitis.

OBJECTIVES We attempted to clarify the mechanism underlying lower bile duct stricture in autoimmune pancreatitis. METHODS Imaging and histologic finding of the bile duct were assessed for 73 patients with autoimmune pancreatitis to clarify whether IgG4-related biliary inflammation or pancreatic head swelling is associated with lower bile duct stricture. RESULTS Lower bile duct stricture was found in 59 (81%) patients. Pancreatic head swelling was significantly more frequent among patients with lower bile duct stricture than those patients without lower bile duct stricture (53 [90%] vs 4 [29%]; P < 0.01). Intraductal ultrasonography findings revealed lower bile duct wall thickening in 21 (95%) of the 22 patients with lower bile duct stricture, and the lower bile duct wall of the patients with pancreatic head swelling was significantly thicker than those patients without pancreatic head swelling (P = 0.028). Among the 38 patients with lower bile duct biopsies, 14 (37%) exhibited abundant IgG4-bearing plasma cell infiltration. Among the patients with lower bile duct stricture, an IgG4-related inflammation seemed to exert a dominant effect under limited conditions, including concomitant middle bile duct stricture and neither pancreatic swelling nor pancreatic duct stricture in the head region. CONCLUSIONS Both pancreatic head swelling and IgG4-related biliary inflammation affect lower bile duct stricture, which may be included in IgG4-related sclerosing cholangitis. Pancreatic head swelling affects IgG4-related biliary wall thickening.