Chapter 59 - Autoimmune Pancreatitis and Immunoglobulin G4–Related Disease

Abstract

Immunoglobulin G4–related disease (IgG4-RD) is a recently established systemic disease that is characteristically associated with IgG4 and is considered to be caused by autoimmune mechanisms. The clinical features of IgG4-RD can be summarized as (1) systemic distribution; (2) imaging findings of swelling, nodules, and/or wall thickening; (3) high serum IgG4 concentration; (4) abundant lymphoplasmacytic and IgG4-bearing plasma cell infiltration in affected organs; (5) a favorable response to corticosteroid therapy; and (6) combination with other IgG4-RDs simultaneously or in a metachronous fashion. Although IgG4-RD is now attracting worldwide interest, its concept was originally established based on the intense study of IgG4 in autoimmune pancreatitis (AIP) to open the gateway from AIP to IgG4-RD. It has become evident that IgG4-RD has systemic organ manifestations, but the exact prevalence and clinical features of individual IgG4-RDs remain unclear. Numerous pathological, immunological, and genetic investigations have provided considerable insight into the pathogenesis of IgG4-RD, especially regarding autoimmune mechanisms. Accordingly, glucocorticoids are regarded as the first-line agent for active and untreated IgG4-RD, although steroid-sparing agents and B-cell depletion with rituximab may also be considered in exceptional cases. Despite reports of a close association with various malignancies, the long-term prognosis of IgG4-RD appears to be favorable.