[1599] Autoimmune Pancreatitis (AIP) Type 1 and Type 2: An International Consensus Study on Histopathologic Diagnostic Criteria.

Lizhi Zhang, Suresh Chari, Thomas Smyrk, Vikram Deshpande, Gunter Kloppel, Motohiro Kojima, Xiuli Liu, Daniel Longnecker, Mari Mino-Kenudson, Kenji Notohara, Manuel Rodriguez-Justo, Amitabh Srivastava, Giuseppe Zamboni, Yoh Zen. Mayo Clinic, Rochester; Massachusetts General Hospital, Boston; University of Kiel, Germany; National Cancer Center Hospital East, Kashiwa Chiba, Japan; Cleveland Clinic; Dartmouth-Hitchcock Medical Center, Lebanon; Kurashiki Central Hospital, Japan; University College London, United Kingdom; University of Verona, Italy; King's College London, London, United Kingdom

Background: There is lack of consensus among pathologists regarding diagnostic criteria and typing of AIP. The goal of this study was to develop and validate consensus diagnostic criteria for AIP and its types.
Design: As a part of the AIP International Co-operative Study Group, 13 pathologists from five countries participated in this two-phase study to develop diagnostic criteria for AIP types 1 and 2 (Phase I) and validate them (Phase II). A virtual library of 40 resected pancreata of AIP and other forms of chronic pancreatitis (CP) was constructed at PathXchange.org. All slides were reviewed online. Readers filled out a questionnaire for key histopathologic findings, final diagnosis and AIP type.
Results: AIP had distinguishing features from alcoholic and obstructive forms of CP, including periductal lymphoplasmacytic infiltrate, inflamed cellular stroma with storiform fibrosis, obliterative phlebitis, and granulocytic epithelial lesion (GEL). Although there was overlap, two types (type 1 and type 2) were recognized. Type 1 AIP had dense periductal lymphoplasmacytic infiltrate with storiform fibrosis and obliterative phlebitis, while type 2 was distinguished from type 1 by GEL and less prominent lymphoplasmacytic infiltrate and storiform fibrosis. Diagnostic criteria for AIP and its types were proposed according to the results from the top 5 reviewers in phase I. The inter-observer agreement was significantly improved in phase II study. The multi-rater Kappa statistic among all reviewers for diagnosing AIP and distinguishing its types were increased from 0.59 to 0.7 and from 0.08 to 0.54 respectively. For the top 5 reviewers, there was almost perfect agreement for diagnosing AIP in both phases, and the Kappa statistic for distinguishing its types was increased from 0.39 to 0.80.
Conclusions: In resected pancreata, AIP can be distinguished from other forms of CP with substantial interobserver agreement. There are two distinct histopathologic types of AIP. The histopathologic diagnostic criteria for AIP and its types proposed by this international consensus study can be used as guidelines by general pathologists.
Category: Liver & Pancreas

Monday, February 28, 2011 1:00 PM

Platform Session: Section D, Monday Afternoon

 

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