Autoimmune pancreatitis. An update

Autoimmune pancreatitis (AIP) is a rare disease, the pathophysiological understanding of which has been greatly improved over the last years. The most common form, type 1 AIP belongs to the IgG4-related diseases and must be distinguished from type 2 AIP, which is a much rarer entity associated with chronic inflammatory bowel disease. Clinically, there is an overlap with pancreatic cancer. Imaging and further criteria, such as serological and histological parameters are utilized for a differentiation between both entities in order to select the appropriate therapy and to avoid the small but ultimately unnecessary number of pancreatectomies. The diagnostics of AIP are complex, whereby the consensus criteria of the International Association of Pancreatology have become accepted as the parameters for discrimination. These encompass five cardinal criteria and one therapeutic criterion. By applying these criteria AIP can be diagnosed with a sensitivity of 84.9 %, a specificity of 100 % and an accuracy of 93.8 %. The diagnosis of AIP is accomplished by applying several parameters of which two relate to imaging. As for the routine diagnostics of the pancreas these are ultrasound, computed tomography (CT) and magnetic resonance imaging (MRI). Important for the differential diagnosis is the exclusion of signs of local and remote tumor spread for which CT and MRI are established. The essential diagnostic parameter of histology necessitates sufficient sample material, which cannot usually be acquired by a fine needle biopsy. CT or MRI are the reference standard methods for identification of the optimal puncture site and imaging-assisted (TruCut) biopsy. In patients presenting with unspecific upper abdominal pain, painless jaundice combined with the suspicion of a pancreatic malignancy in imaging but a mismatch of secondary signs of malignancy, AIP should also be considered as a differential diagnosis. As the diagnosis of AIP only partially relies on imaging radiologists also have to be aware of the clinical, serological and histological parameters for AIP in order to guide clinicians towards the correct diagnosis. Only in this way can the highly efficient steroid therapy be initiated and otherwise possibly severe forms of therapy be avoided. (orig.)