Current challenges in the diagnosis of autoimmune pancreatitis

Autoimmune pancreatitis (AIP), an inflammatory disease of the pancreas first described in Japan, is characterized by a tumefactive lesion in the pancreas, thus clinically resembling pancreatic cancer. Currently, it is classified into two variants – type 1 AIP and type 2 AIP, each with distinct clinico-pathologic and epidemiologic features. Type 1 AIP is a part of IgG4 related disease, a generalized multi-systemic disease, and recapitulates its clinical and pathologic features. Type 2 AIP is an isolated pancreas-centric disease, and is not associated with elevated tissue or serum IgG4. Histologically, type 1 AIP is characterized by storiform-type fibrosis and obliterative phlebitis, while type 2 disease shows granulocytic epithelial lesions. Even when AIP is suspected, a diagnosis should seldom be made in isolation, but should be rendered only after collating clinical and radiologic data. Steroids remain the mainstay of treatment for both variants of AIP, although other immunosuppressive drugs like rituximab have proven successful. In this review, we summarize the current knowledge of this entity and discuss diagnostic challenges, with particular emphasis on the interpretation of needle biopsies. Recognition of AIP as a mimic of pancreatic cancer is imperative to reduce unnecessary morbidity and mortality associated with pancreatic surgery.