Abstract
Autoimmune pancreatitis (AIP) is acknowledged as a benign ailment with swift responsivity to corticosteroid treatment (CST). Though past assumptions dismissed its connection to cyst formation, a few instances of AIP-linked pancreatic cysts (PCs) have been documented. While some cases responded positively to CST, others demonstrated resistance, necessitating intervention. Our case is a 50-year-old male with a known diagnosis of type 1 AIP. This case presents a specific adverse drug reaction of glucocorticoid that causes diabetes mellitus. Glucocorticoid was tapered due to clinical improvement and diabetes complications but also caused multiple flares. Additionally, in several months, CT showed progressive enlarging multi-cystic pancreatic head lesions, which cause constriction at the distal duodenal outlet and biliary ductal dilation. This case presents a specific adverse drug reaction of glucocorticoid that causes diabetes mellitus. Meanwhile, the fast-growing multi-cysts in the pancreatic head after treatment of type 1 AIP were very rare.