Background & Aims: Autoimmune pancreatitis (AIP) and pancreatic cancer (PaC) have similar presentations; a diagnostic strategy is needed to distinguish the 2 diseases. Methods: We compared computed tomography images (for pancreas and other organ involvement), serum IgG4 levels, histology data, and the response to steroids between patients with AIP (n = 48) and those with PaC (n = 100). Results: Pancreatic imaging findings stratified patients into 3 groups. Group 1 was highly suggestive of AIP, with diffuse pancreatic enlargement without group 3 features (n = 25, 100% AIP). Group 2 was indeterminate, with normal-sized pancreas or focal pancreatic enlargement without group 3 features (n = 20, 75% AIP). Group 3 was highly suggestive of PaC, with presence of >1 low-density mass, pancreatic duct cutoff, or upstream pancreatic atrophy (n = 103, 92% PaC). Although all patients in group 1 had AIP, only 20 of the 25 patients had increased serum IgG4 levels and/or other organ involvement. Of the patients in groups 2 and 3 who did not have cancer, all those with serum IgG4 levels >2-fold the upper limit of normal or a combination of increased serum IgG4 levels and other organ involvement (n = 15) had AIP. In AIP subjects without supportive serologic evidence or other organ involvement (n = 14), diagnosis required pancreatic core biopsy (n = 7), steroid trial (n = 5), or resection (n = 2). Conclusions: PaC can be distinguished from AIP by pancreatic imaging, measurement of serum IgG4 levels, and determination of other organ involvement. However, a pancreatic core biopsy, steroid trial, or surgery is required for diagnosis in approximately 30% of patients with AIP. To view this article's video abstract, go to the AGA's YouTube Channel.
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