IgG4 Pancreatitis Presenting as a Mass: Unraveling a Diagnostic Illusion

Autoimmune pancreatitis is a fibroinflammatory subtype of chronic pancreatitis resulting from aberrant immune responses. Currently, there are two forms of autoimmune pancreatitis: type 1 (T1-AIP) or lymphoplasmacytic sclerosing pancreatitis and type 2, also known as idiopathic duct-centric chronic pancreatitis. T1-AIP is often identified as the pancreatic appearance of immunoglobulin 4 (IgG4)-related disease. T1-AIP commonly appears in the seventh decade of life with a considerable male predominance, frequently associated with elevations in serum IgG4 levels and IgG4-positive cells on tissue biopsy. Type 1 and 2 autoimmune pancreatitis glucocorticoid steroid treatment leads to clinical remission in almost 100% of type 1 and 2 cases. Here, we present a case of an adult who presented with an incidental pancreatic head and tail mass on CT imaging with elevated serum IgG4 levels. He was started on steroid therapy with eventual clinical remission of his disease. This case highlights the rarity of autoimmune pancreatitis and the work-up required to rule out malignancy of the pancreatic mass.