Autoimmune pancreatitis and IgG4-related systemic diseases.

Autoimmune pancreatitis (AIP) is a rare form of chronic pancreatitis that is characterized by lymphoplasmacytic infiltrate, storiform fibrosis, obliterative phlebitis, and increased IgG4(+) plasma cells. Serum IgG4 levels usually are elevated. Patients with AIP frequently have disease affecting other organs or sites; these tissues show similar histologic changes, including increased IgG4(+) plasma cell infiltrate and response to corticosteroid therapy. A new clinicopathologic concept of IgG4-related systemic disease (ISD) has been proposed. These diseases often are not limited to the pancreas, and the pancreas may not be involved at all. In this article, we review the literature and our own experience to detail the clinicopathologic features of AIP and extrapancreatic lesions in ISD.