Clinical and Diagnostic Features
Type 1 AIP
The most common clinical presentation of type 1 AIP is obstructive jaundice in older adult patients. Patients usually have minimal or no abdominal pain. In a series reported by Kim et al, 65% of patients with AIP had painless jaundice caused by biliary obstruction. Weight loss can be present in patients with chronic symptoms. This weight loss usually results from impaired digestion and decreased appetite secondary to pancreatic exocrine and endocrine dysfunctions. DM is seen in approximately 60% of patients with active AIP and mostly responds to steroid therapy. AIP may initially manifest as recurrent acute pancreatitis and later chronic pancreatitis with the presence of pancreatic duct stones in the long term in up to 7% of patients. Parenchymal atrophy, calcification, and exocrine and endocrine deficiencies mark the burnt-out phase of this chronic disease.
In addition to the above pancreatic manifestations, type 1 AIP exhibits extrapancreatic features that are related to the presence of antigens in the target organs. Type 1 AIP has been considered to be a pancreatic manifestation of IgG4-related systemic disease, and Table 1 shows different organ involvement in IgG4-related systemic disease. IgG4-related cholangiopathy is a biliary manifestation of IgG4-related systemic disease and is characterized by increased serum IgG4 levels, infiltration of IgG4-positive plasma cells with storiform fibrosis and/or obliterative phlebitis in the thickened bile duct wall, and steroid responsiveness.
Type 2 AIP
Patients with type 2 AIP are usually younger and more frequently present with abdominal pain and other symptoms of acute pancreatitis. Type 2 AIP involves only the pancreas and does not have extrapancreatic manifestations. IBD is seen in approximately 30% of patients with type 2 AIP. This type of AIP is less likely to have recurrent disease compared with type 1 AIP and is experienced in only 9% of patients; these individuals usually do not have long-term sequelae.