Clinical characteristics, imaging diagnostic accuracy, and prognosis of autoimmune pancreatitis: A real‐world study in China

Objective In this study we aimed to comprehensively evaluate the clinical features and treatment outcomes of Chinese patients with autoimmune pancreatitis (AIP) through a single‐center real‐world study. Methods Patients diagnosed with AIP in Changhai Hospital, Naval Medical University from January 2014 to December 2021 were included. Baseline characteristics, laboratory test results, cross‐sectional imaging and endoscopic ultrasound (EUS) findings, and long‐term follow‐up data were obtained. The differences in these characteristics between type 1 and type 2 AIP patients were analyzed. Results Among all 320 patients, 271 (84.7%) and 49 (15.3%) had type 1 and type 2 AIP, respectively. The most common initial symptom was abdominal discomfort (58.1%), followed by obstructive jaundice (32.5%). Extrapancreatic organ involvement was identified in 126 (39.4%) patients, with the biliary system being the most commonly involved (36.6%). Elevated serum IgG4 level was rare in type 2 AIP patients. The diagnostic accuracy of computed tomography (CT), magnetic resonance imaging (MRI), and EUS for definitive and probable AIP were 78.0%, 68.7%, and 80.5%, respectively. EUS‐guided tissue acquisition with immunohistochemical staining helped establish a final diagnosis in 39.7% of patients. During the follow‐up period of 60 months, 18.6% of patients experienced relapse. The 1‐, 3‐, and 5‐year relapse rates were higher in type 1 AIP patients, with an accumulated rate of 8.0%, 12.6%, and 15.1%, when compared with those with type 2 AIP. Conclusions Type 2 AIP is not uncommon in Chinese population. The diagnostic accuracy of CT and EUS for AIP might be superior to that of MRI.