Autoimmune Pancreatitis Masquerading as Pancreatic Cancer: A Case Report and Literature Review.

Autoimmune pancreatitis (AIP) is a chronic fibro-inflammatory disease of the pancreas that belongs to the spectrum of immunoglobulin G-subclass 4-related diseases (IgG4-RD). It is sometimes associated with a visible pancreatic mass mimicking pancreatic cancer on imaging. The most common presentations include abdominal pain and obstructive jaundice in elderly men. Similar to other IgG4-RD, it can cause cholangiopathy, nephritis, orbital pseudotumor, and extensive lymphadenopathy. Here, we present the case of a 53-year-old female with abdominal pain and obstructive jaundice, which was diagnosed as AIP in association with significantly elevated tumor marker carbohydrate antigen 19-9 (CA 19-9). She responded to biliary decompression and steroid treatment, potentially avoiding extensive surgical intervention. On follow-up, her CA 19-9 and IgG4 levels were normalized. AIP should be high on the differential diagnosis during the evaluation of a pancreatic mass.