Auto immune pancreatitis (AIP) is an uncommon form of chronic pancreatitis that has been divided into type 1 and type 2 which have distinct histopathology and clinical features. Type 1 AIP seems to be the pancreatic manifestation of an IgG4-related systemic disease, characterized by elevated IgG4 serum levels, infiltration of IgG4-positive plasma cells and extrapancreatic lesions. When manifesting as a focal disease in the pancreas, it can be challenging to differentiate it from pancreatic cancer (PC). Because AIP is typically responsive to steroid therapy without the need for resection, differentiation between these two diseases is critical. We report the case of a 56-year-old man with initial suspect of PC, and final diagnosis of type 1 AIP according to the International Consensus Diagnostic Criteria (ICDC) without elevated levels of serum IgG4 or need for a histology sample. We take a review of literature in order to improve the diagnostic accuracy of AIP and describe clinical and imaging features to differentiate it from PC and avoid unnecessary surgery due to misdiagnosis.

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