1.8 Diagnosis Criteria for AIP
1.8.1 History
The world's first diagnostic criteria for AIP were proposed by the Japan Pancreas Society（JPS）in 2002（Members of the Criteria Committee for Autoimmune Pancreatitis of the Japan Pancreas Society 2002）.The criteria consisted of three diagnostic items，（1）imaging findings（mandatory），（2）serological and（3）pathological findings.The 2002 criteria defined the length of MPD narrowing as more than 1/3 of the whole pancreas on endoscopic retrograde pancreatography（ERP）to avoid misdiagnosis of pancreatic cancer as AIP.Therefore，localized-type AIP could not be diagnosed according to the 2002 JPS criteria.The 2002 JPS criteria were revised in 2006（Okazaki et al.2006）.In this revision，the length of MPD narrowing was eliminated and IgG4 was incorporated as a serological item.
Fig.11.2 Biopsy specimens obtained by EUS-FNA using a 22-G needle.（a）Infiltration of plasma cells and lymphocytes with fibrosis（storiform fibrosis）（H&E，X100）.（b）Immunostaining for IgG4 showing infiltration of IgG4-positive plasma cells（X100）
Thereafter，diagnostic criteria were proposed worldwide including in Korea（Kim et al.2006）and the United States（Chari et al.2006）.Additional diagnostic features，including various appearances on computed tomography（CT），OOI andresponse to steroids were incorporated in these diagnostic criteria.The diagnostic criteria in the United States，namely HISORt criteria，were revised in 2009.The revised HISORt criteria covered both LPSP and IDCP/GEL（Chari et al.2009）.However，the lack of common diagnostic criteria for AIP was a large obstacle for international comparative studies.
In 2009，experts in this field discussed the consensus on the diagnostic criteria for AIP in Honolulu，Hawaii.It was agreed that the clinical phenotypes associated with LPSP and IDCP/GEL should be distinguished，but，the terminology was controversial.Most experts agreed that LPSP and IDCP/GEL should be referred to as type 1 and type 2 AIP，respectively，but others objected to the use of the term‘autoimmune’to describe IDCP（Chari et al.2010）.During the next year，there was further discussion in Fukuoka，Japan，and，finally，the ICDC for AIP were proposed（Shimosegawa et al.2011）.The ICDC took global differences in clinical practice into consideration to be used worldwide to safely diagnose AIP without misdiagnosing pancreatic cancer as AIP.
Fig.11.3 Other organ involvement.（a）Endoscopic retrograde cholangiopancreatography showing strictures of the bile duct in the hilar hepatic lesions（red arrow）.（b）Swelling of the submandibular glands（red arrows）.（c）18F-FDG uptake by the submandibular glands is shown on 18F-fluorodeoxyglucose positron emission tomography（red arrows）
1.8.2 Overview of the ICDC
In the ICDC，AIP is diagnosed according to the parenchymal imaging（P），ductal imaging on ERP（D），serology（S），other organ involvement（OOI），histology of the pancreas（H），and response to steroid（Rt；optional）.Each cardinal feature is categorized as level 1 or level 2 according to the reliability for diagnosis.
AIP is classified into two subtypes:type 1 related to LPSP and type 2 related to IDCP/GEL.Type 1 and type 2 AIP are diagnosed according to the independent diagnostic criteria.Table 11.1 summarizes the level 1 and level 2 criteria for type 1 AIP in ICDC.If imaging findings of the pancreatic parenchyma yield typical findings（diffuse enlargement with delayed enhancement），type 1 AIP can be definitively diagnosed if there are any non-D level 1/level 2 findings（Table 11.2）.If pancreatic imaging findings were indeterminate（segmental or focal enlargement with delayed enhancement），two or more level 1（+level 2D）findings are required to diagnose type 1 AIP definitively.If the core biopsy specimens or resected pancreatic tissues indicate LPSP，definitive type 1 AIP can be diagnosed based on the histological findings alone.
Table 11.1 Level 1 and Level2 criteria for type 1 AIP in ICDC
aAtypical:Some AIP cases may show low-density mass，pancreatic ductal dilatation or distal atrophy.Such atypical imaging findings in patients with obstructivej aundice and/or pancreatic mass are highly suggestive of pancreatic cancer.Such patients should be managed as pancreatic cancer unless there is strong collateral evidence for AIP and a thorough workup for cancer is negative
bEndoscopic biopsy of duodenal papilla is a useful adjunctive method because ampulla is often involved pathologically in AIP
cDiagnostic steroid trial should be conducted carefully by pancreatologists with caveats only after negative workup for cancer including endoscopic ultrasound-guided fine-needle aspiration
Table 11.2 Diagnosis of definitive and probable type 1 AIP using ICDC
aLevel 2 D is counted as level 1 in this setting
ICDC International Consensus Diagnostic Criteria，AIP autoimmune pancreatitis，LPSP lymphoplasmacytic sclerosing pancreatitis
Table 11.3 Level1 and level 2 criteria for type 2 AIP(https://www.daowen.com)
a，bSee Table 11.1
Table 11.3 summarizes the level 1 and level 2 criteria for type 2 AIP.Histological examination is required for a diagnosis of type 2 AIP.The level 1 histological findings of GEL are sufficient for a definitive diagnosis of type 2 AIP（Table 11.4）.Alternatively，in the case of level 2 histological findings，definitive type 2 AIP can be made if the patient has inflammatory bowel disease and responds to steroids.
Cases that have level 1 or level 2 ductal imaging findings and respond to steroids，without other cardinal features of AIP，are diagnosed as AIP-not otherwise specified（AIP-NOS）.These cases should be carefully followed up，because other diseases are possible（Table 11.5）.
Table 11.4 Diagnosis of definitive and probable type 2 AIP using ICDC
AIP autoimmune pancreatitis，IDCP idiopathic duct-centric chronic pancreatitis
Table 11.5 Diagnosis of AIP-not otherwise specified using ICDC