5.4 Application of Diagnostic ERCP
There have been profound differences of diagnostic criteria and algorithms for CP；hence the application of ERCP varies accordingly.
5.4.1 Applying ERCP to Various Diagnostic Systems
The initial efforts for a consensus definition of CP were conducted in Marseille and Rome in 1963，1984 and 1988（Sarles 1965；Singer et al.1985；Sarles et al.1989）.However，it was the Cambridge Classification that first recommendedERCP as one of the diagnostic criteria in 1984（Sarner and Cotton 1984；Axon et al.1984），which was recently adopted by the Italian consensus guidelines（Frulloni et al.2010）and Spanish recommendations（Martinez et al.2013）.
Table 7.5 Morphologic classification of chronic pancreatitis by ERCP（Reprint with permission from Cremer et al.1989）
MPD main pancreatic duct
Fig.7.15 Diagram of morphologic classification of chronic pancreatitis by ERCP（Reprint with permission from Gastrointest Endosc，Cremer et al.1989）
In 1996，a workshop of experts developed a clinically based classification system for alcoholic chronic pancreatitis（ACP）in Zurich.They employed the Cambridge criteria and categorized moderate or marked changes as definite ACP，and mild changes as probable ACP（Ammann 1997，1998）.
The Japan Pancreas Society grouped their own criteria into definite CP and probable CP，with the ERCP findings different from each other:ERCP may show（a）irregular dilatation of pancreatic duct branches of variable intensity with scattered distribution throughout the entire pancreas or（b）irregular dilatation of the MPD，and branches proximal to complete or incomplete obstruction of the MPD（with pancreatic stones or protein plugs）in definite CP，whilethe image in those suffering from probable CP would demonstrate irregular dilatation of the MPD alone，intraductal filling defects suggestive of noncalcified pancreatic stones or protein plugs（Homma et al.1997）.Also，the concept of early CP was proposed by the Japanese Society of Gastroenterology in 2009（Shimosegawa et al.2010）and the latest revised guidelines in 2015 pointed out that irregular dilatation of more than three duct branches on ERCP is sufficient to confirm early CP（Ito et al.2016）.
However，the Asia-Pacific consensus did not adopt the Japanese criteria and it doubted whether early or less advanced changes of CP could be detectable on ERCP；meanwhile，it listed ductal changes on ERCP as one of the independent diagnostic criteria for CP（Tandon et al.2002）.(https://www.daowen.com)
By contrast，the role of diagnostic ERCP may be limited by the American Gastroenterological Association because experts considered it not only risky and costly，but also unable to accurately detect minimal or subtle ductal abnormalities which are subject to variability in interpretation and difficulty in identification（Etemad and Whitcomb 2001）.Specifically，the American Society for Gastrointestinal Endoscopy recommended that ERCP should be reserved for patients in whom the diagnosis is still unclear after noninvasive pancreatic function testing or other noninvasive（CT，MRI）or less invasive（EUS）imaging studies have been performed（Adler et al.2006）.After then，the guidelines published by the 2014）.Other grading or classification systems just mentioned ERCP as one of the radiological evidences facilitating the diagnosis（Ramesh 2002；Bagul and Siriwardena 2006）.
When it comes to autoimmune pancreatitis（AIP），the diagnostic value of ERCP is highly controversial among several centers（Chari et al.2006，2010；Okazaki et al.2009，2010；Kamisawa et al.2010；Otsuki et al.2008；Shimosegawa et al.2011；Church et al.2007；Raina et al.2009）.One of the widely divergent views is that the Japanese consensus guidelines have made ERCP a mandatory diagnostic criterion（Kamisawa et al.2010）while others only include ERCP as a selective test.American Pancreatic Association summarized that ERCP could still provide some useful diagnostic information though it is rarely used as a diagnostic modality in CP（Conwell et al.2014）.
Similarly，the German clinical practice guidelines emphasized that only in the case of indefinite diagnosis yielded by all of other imaging methods should ERCP be carried out after the German Society of Digestive and Metabolic Diseases added various imaging modalities into a modified Cambridge Classification and took the changes in the pancreatic parenchyma into consideration（Mayerle et al.2013；Schreyer et al.
5.4.2 Differentiating CP from Other Diseases by ERCP
It may be useful to perform ERCP for those patients in whom other methods are unavailable，nondiagnostic or make differential diagnosis difficult.
There may be pathological changes in the pancreatic duct in the advanced stage of CP or as a result of pancreatic neoplasms（such as ductal adenocarcinoma and intraductal papillary mucinous neoplasm）that are hard to differentiate，stimulating the utility of ERCP if necessary（Shamamian et al.2009；Devereaux and Binmoeller 2000；Brugge 2013）.On the basis of more pathognomonic changes found in the pancreatic duct，it is possible，with the aid of pancreatic juice collecting，pancreatic duct brushing，intraductal tissue sampling or intraductal pancreatic endoscopy via ERCP，to distinguish correctly between the two disorders in most of the patients（Uhl et al.2004）.Techniques to enhance the accuracy of cytology are in progress after the additional detection of telomerase activity，K-ras mutations，p53 and other biological molecular markers，especially for patients without pancreatic calcifications（Shamamian et al.2009；Arvanitakis et al.2004）.
ERCP may also be required in the case of AIP when other imaging procedures fail to make a differential diagnosis.An international multicenter study（Sugumar et al.2011）suggested that four distinct ductal features can be used to differentiate cancer from AIP.Long strictures involving more than one third of the duct length，strictures that do not result in an upstream dilatation of the duct，strictures from which side branches arise and the presence of multiple strictures in the duct are more likely to be caused by AIP than by cancer.