Immunoglobulin G4 (IgG4)‐related autoimmune hepatitis and IgG4‐hepatopathy: A histopathological and clinical perspective

Abstract Immunoglobulin G4 (IgG4)‐related disease (IgG4‐RD) is a chronic inflammatory disease that simultaneously or consecutively involves multiple organs of the body. It is characterized by elevated serum IgG4 levels and massive infiltration of IgG4 + plasma cells in the damaged tissues. IgG4‐related autoimmune hepatitis (IgG4‐AIH) and IgG4‐hepatopathy are relatively new entities that have been proposed as a phenotype of IgG4‐RD in the liver. Immunoglobulin G4‐AIH is defined as a disorder with serological, histopathological, and clinical features of both IgG4‐RD and AIH, simultaneously satisfying the diagnostic criteria of both classical AIH and IgG4‐RD. Although there are several case reports and studies of IgG4‐AIH among the published works, no consensus regarding the histopathological characteristics of IgG4‐AIH has been established, and its clinical implications remain obscure. Immunoglobulin G4‐hepatopathy is defined as a comorbidity of IgG4‐RD in the liver, and patients not meeting the diagnostic criteria of classical AIH could be diagnosed with IgG4‐hepatopathy. Numerous issues regarding these diseases, especially their epidemiology, histopathological and clinical characteristics, and treatment response to corticosteroids, remain unsolved, and need to be determined to establish the disease concepts of IgG4‐AIH and IgG4‐hepathopathy.