On the Relationship of AIP to Systemic Disease
AIP patients sometimes demonstrate extrapancreatic lesions such as intra- and extra-bile-duct sclerosing lesions (sclerosing cholangitis) , retroperitoneal fibrosis and sialadenitis. These diseases may arise synchronously or asynchronously to AIP and show histological findings similar to those of AIP, namely lymphoplasmacytic infiltration and fibrosis with IgG4-positive plasmacytes. Especially sclerosing cholangitis presents the same histology as AIP: centro-ductal lymphoplasmacytic infiltration and sclerosing fibrosis with IgG4-positive plasmacytes and obstructive phlebitis. Therefore a comprehensive concept of IgG4-related sclerosing disease  or multifocal fibrosclerosis is proposed, and AIP can be considered a pancreatic manifestation of the concept.
Klöppel et al. classified AIP into two subgroups [9, 10]: either with or without the presence of granulocytic epithelial lesions (GEL). GEL is defined as granulocytic infiltration into the ductal epithelium, corresponding to 'crypt abscess' in ulcerative colitis. Klöppel et al. selected AIP cases from surgically resected cases of benign inflammatory pancreatic disease without pseudocysts, calculi, pancreas divism, duodenal wall cysts or associated pancreatitis, or a history of alcohol abuse, cholelithiasis or choledocholithiasis.
However, Notohara et al. at the Mayo Clinic summarized inflammatory pancreatic cases showing dense inflammatory cell infiltration around the pancreatic ducts, and classified them as either lymphoplasmacytic sclerosing pancreatitis (LPSP) or idiopathic duct-centric chronic pancreatitis (IDCP) . Although this group does not use the terms 'AIP' or 'IgG4-positive plasma-cyte' in their report, they summarized the cases similar to AIP showing characteristic features of narrowing of the MPD on ERP. IDCP is characterized by prominent lobular inflammation consisting of edema and infiltrating neutrophils, lymphocytes and plasmacytes. 'LPSP' is the same as the term described by Kawaguchi , who used it to describe inflammatory pancreatic lesions with cholangitis. The term 'LPSP' has been used by two different authors to indicate the same lesion, and Japanese AIP cases may correspond to 'LPSP'.
Currently, there are some issues that remain to be resolved regarding the histology of AIP: whether 'AIP with GEL' and 'IDCP' are the same lesion, whether 'AIP without GEL' and 'LPSP' are the same lesion, and whether 'LPSP' is 'true AIP'. It is also problematic that there is one case showing features of both LPSP and IDCP among the cases reported by Notohara, and it remains unclear whether eosinophilic pancreatits is 'AIP with GEL' . Furthermore, we have one case of LPSP with eosinophils (mentioned above).
Based on the major clinicopathological features of AIP described by Japanese researchers, we conclude that AIP should be considered one distinct clinicopathological disease entity satisfying the features described in the introduction to this chapter.
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Department of Human Pathology, Juntendo University School of Medicine 2-1-1, Hongo, Bunkyo-ku Tokyo 113-8421 (Japan)
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