Clinical features and long‐term prognosis of type 1 autoimmune pancreatitis based on the location of bile duct lesions

Abstract Background/Purpose Type 1 autoimmune pancreatitis (AIP) frequently involves biliary lesions and poses diagnostic and therapeutic challenges. We aimed to evaluate the clinical features and long‐term prognosis of type 1 AIP with a focus on the locations of bile duct lesions. Methods In this retrospective study, 159 patients with type 1 AIP were included. Patients were classified on the basis of the location of bile duct strictures, and clinical outcomes, including relapse rates and steroid dependency, were analyzed. Results Eighty‐nine (56%) patients had bile duct involvement. Forty‐nine patients (30.8%) experienced relapse, with a significantly higher cumulative relapse rate in cases of stricture or wall thickening upstream of the intrapancreatic bile duct (3 years: 24% vs. 37.1%, p  < .001). These patients also had a significantly higher rate of two or more relapses than did the patients without stricture or wall thickening (5.1% vs. 19.5%, p  = .01). Two patients with stricture and dilation up to the intrahepatic bile ducts became steroid‐dependent and were treated with azathioprine. Conclusions Patients with type 1 AIP with biliary lesions involving upstream strictures or wall thickening, especially those with stricture and dilation extending into the intrahepatic bile ducts, are at high risk of relapse and may become steroid dependent.