Autoimmune pancreatitis associated with retroperitoneal fibrosis mimicking cholangiocarcinoma.

Autoimmune pancreatitis (AIP) is a rare systematic autoimmune disease that causes chronic pancreatitis. Type 1-AIP (IgG4-related disease) may involve other organs as well. In this report we are presenting a case of a 74-year-old man with obstructive abdominal pain jaundice, mild and a history of retroperitoneal fibrosis and hydronephrosis. Labs were remarkable for hyperbilirubinemia, high serum IgG4 levels, mildly elevated CA 19-9, elevated rheumatoid factor and new onset diabetes. MRI revealed pancreatic enlargement, dilated intrahepatic bile ducts and stricture of the distal common bile duct concerning for cholangiocarcinoma. EUS-FNA biopsy was negative for malignancy but showed findings of pancreatitis. The diagnosis of type 1-AIP was made and the patient was treated with steroids. After one month of treatment jaundice and MRI findings resolved. It is important to include AIP in the differential diagnosis of pancreatic conditions causing obstructive jaundice, especially in the presence of other autoimmune conditions like retroperitoneal fibrosis.