Autoimmune pancreatitis is a specific type of chronic pancreatitis mediated by autoimmunity and characterized by enlargement of the pancreas and irregular stenosis of the pancreatic duct. The exact pathogenesis of the disease is unclear. Lymphoplasmacytic infiltration with pancreatic tissue fibrosis and a large number of IgG4-positive cells on immunohistochemistry are its characteristic pathological manifestations. In addition to the pancreas, some patients may also be combined with biliary ductitis, salpingitis, lymph node enlargement, retroperitoneal fibrosis, interstitial nephritis, pulmonary interstitial fibrosis and other extra-pancreatic lesions. The clinical manifestations of AIP are non-specific and can be characterized by obstructive jaundice, varying degrees of abdominal pain, back pain, malaise, weight loss, etc. Painless obstructive jaundice is the most common, and about 15% of patients are asymptomatic. 40%-90% of patients with AIP have extra-pancreatic organ involvement, including cholangitis, mediastinal or abdominal lymph node enlargement, interstitial nephritis, retroperitoneal fibrosis, salpingitis, pulmonary interstitial fibrosis, etc. salpingitis, and interstitial pulmonary fibrosis. Extra-pancreatic manifestations may occur simultaneously with or before or after AIP. 50%-70% of patients with AIP have combined diabetes mellitus or abnormal glucose tolerance. Serology IgG can be divided into 4 subclasses, of which IgG4 accounts for only 3-6% of total serum IgG. Previously, it was thought that elevated IgG4 was only seen in a few diseases such as allergic dermatitis, certain parasitic infections, common aspergillosis, and deciduous aspergillosis. However, since Hamano et al. first reported the correlation between IgG4 and AIP, many researchers have conducted in-depth studies on the sensitivity and specificity of IgG4 for the diagnosis of AIP. To date, elevated serum IgG4 has become the most valuable serological indicator for the diagnosis of AIP. The sensitivity and specificity of IgG4 for the diagnosis of AIP have fluctuated from 67% to 94% and the specificity from 89% to 100% in several studies, and the different settings of the upper normal limit of IgG4 may be one of the reasons for the differences in the results. For example, the upper normal limit of IgG4 was set at 135 mg/dl in the Japanese study, 140 mg/dl in the U.S., and 130 mg/dl in Europe. in addition, serum IgG4 levels were elevated in about 5% of normal controls and 10% of patients with pancreatic cancer; in contrast, IgG4 levels were normal in patients with pancreatic histology fully consistent with the AIP diagnosis. Therefore, serum IgG4 cannot be used alone to diagnose AIP, and normal levels do not exclude AIP. other studies have reported that IgG4 combined with total serum IgG and autoantibody tests, including rheumatoid factor, antinuclear antibodies, anti-lactoferrin antibodies and carbonic anhydrase II antibodies, can improve the accuracy of diagnosis. The role of IgG4 in monitoring the efficacy of therapy and predicting relapse is not clear. Studies have shown that IgG4 fails to fall to normal in about 42-63% of patients after hormone therapy, and only a minority of these patients relapse during follow-up. However, serum IgG4 tests are still used clinically to monitor the disease because they are easier to repeat than imaging tests. When only elevated serum indicators are found without clinical symptoms and imaging evidence, it is called serologic relapse. 2.Imaging Imaging performance plays a crucial role in the diagnosis of AIP. In fact, the diagnosis of some cases is inextricably linked to the typical description and valuable hints of the radiologist. From the history of the evolution of diagnostic criteria, it is easy to find that imaging descriptions have been indispensable. The imaging features of AIP are: 1. Pancreas: diffuse, limited or focal enlargement, typically with “salami-like” changes, and in some atypical cases, a localized mass, which needs to be differentiated from pancreatic cancer; 2. Pancreaticobiliary duct: diffuse thinning or limited stenosis of the main pancreatic duct, and localized steep centripetal stenosis when the lesion involves the lower part of the common bile duct. 3. The peripancreatic “sphincter” sign appears due to peripancreatic fluid accumulation, inflammation or adipose tissue fibrosis, which shows slightly lower density in the arterial phase and uniform enhancement in the delayed phase during enhancement. The examination methods available include enhanced CT/MRI, magnetic resonance cholangiopancreatography (MRCP), ultrasound endoscopy, retrograde cholangiopancreatography (ERCP) and intracholangiopancreatic ultrasound (IDUS). In recent years, the role of ultrasound endoscopy in the diagnosis of AIP has become increasingly important, as it can not only observe the pancreatic and biliary systems, but also observe the peripancreatic lymph nodes and perform tissue biopsy. However, the accuracy of ultrasound endoscopy is influenced by factors such as operator experience and equipment. The diagnosis and differential diagnosis of focal AIP is a major clinical difficulty. The literature reports that about 20% of patients with AIP are diagnosed only after surgery for suspected pancreatic cancer. In order to enhance the differential diagnosis, Japan and the United States have published differential diagnostic procedures, both of which consider elevated serum IgG4 to be highly suggestive of AIP. The Japanese procedure is relatively simple, focusing on CT and ERCP manifestations, and considers enhanced CT showing enhanced enhancement of pancreatic lesions, “sphincter” sign or involvement of extra-pancreatic organs, as well as ERCP showing the length of main pancreatic duct stenosis. The diagnosis of AIP is suggested by ERCP showing main pancreatic duct stenosis greater than 3 cm in length, jumping lesions in the main pancreatic duct or dilatation of the main pancreatic duct less than 5 mm in width proximal to the stenosis. Histological examination of the pancreas is recommended for those with normal serum IgG4 and only 1-2 of the above imaging manifestations. Compared with the Japanese procedure, the American procedure is relatively complicated, and in addition to not recommending ERCP as a differential, fine needle aspiration biopsy of the pancreas and experimental hormone therapy were introduced as differential methods. The differential diagnostic value of the two procedures remains to be further evaluated. Diagnosis AIP has its own clinical symptoms, imaging, serology and histological characteristics, but because of the lack of specific indicators, the diagnosis needs to combine the characteristics of all aspects, and sometimes even requires close communication and careful consultation among all related departments including gastroenterology, pancreatic surgery, radiology and pathology. In contrast, AIP responds well to hormones, and a correct diagnosis can avoid unnecessary surgical trauma. Thus, it is especially important to understand and grasp the diagnostic criteria. The diagnostic criteria of AIP have been modified several times, from Japanese and Korean standards to European and American standards and Asian standards, reflecting the process of people’s knowledge of AIP from superficial to in-depth, from typical to atypical, and from limited to comprehensive. Although the various criteria vary, in general, they do not differ from imaging, serology, histology, response to hormone therapy and extra-pancreatic organ involvement. Pancreatic cancer and bile duct cancer are the diseases that must be differentiated. When they cannot be differentiated by various methods, even if experimental hormone therapy is used, it should be done under close observation by a gastroenterologist to avoid delays. Regarding experimental hormone therapy, Moon et al. showed that 2 weeks of experimental treatment with 0.5 mg/(kg.d) prednisolone resulted in significant improvement in imaging, and patients who did not respond to treatment were surgically confirmed to have pancreatic cancer. It should be noted, however, that some pancreatic cancers may also respond to hormonal therapy. Treatment AIP is an autoimmune related disease, which responds well to hormone therapy. Prednisone 0.6 mg/(kg.d) can be chosen as the starting dose, and the maintenance dose is 2.5-5 mg/d. There is no consensus on the duration of maintenance therapy, which can be 1-3 years depending on the disease activity and hormone-related side effects. Some patients with AIP may relapse after hormone reduction or discontinuation, and reapplication may still be effective. Elderly and frail patients who have concerns about hormone application can be treated symptomatically, such as endoscopic stenting for obstructive xanthogranuloma. If hormonal therapy is not effective, the diagnosis should be reconsidered and immunosuppressive therapy can be given if the diagnosis is clear, but the efficacy has not been clearly reported. There have been reports of AIP combined with pancreatic cancer, so it is recommended that patients with AIP be followed up regularly with serological indicators and imaging, even including tumor marker testing. In conclusion, AIP has only been recognized for more than 10 years, and although the diagnostic criteria vary from country to country, in general they are no more than imaging, serology, histology, response to hormone therapy and extra-pancreatic organ involvement. At present, the understanding of AIP in China is still in the initial stage, especially in primary hospitals. However, with the deepening of research and the accumulation of experience, clinicians will have a more comprehensive and systematic understanding of this disease.