A clinicopathological study of IgG4-related autoimmune hepatitis and IgG4-hepatopathy.

Objective: Although IgG4-related autoimmune hepatitis (IgG4-AIH) and IgG4-hepatopathy have been proposed as hepatic phenotypes of IgG4-related disease (IgG4-RD), their definitions and concepts remain insufficiently established. This study aims to conduct a clinicopathological investigation of cases reported as potential IgG4-AIH or IgG4-hepatopathy.

Methods: In previous nationwide epidemiological studies conducted in 2015 and 2018, we registered 1096 cases of IgG4-sclerosing cholangitis (IgG4-SC). Among these, 19 cases were identified as potential IgG4-AIH by the attending physicians, and other 20 cases as potential IgG4-hepatopathy with available liver histology were further evaluated using immunohistochemistry to assess the possibility of IgG4-AIH or IgG4-hepatopathy. For this purpose, we provisionally established diagnostic criteria for IgG4-AIH and IgG4-hepatopathy, primarily based on the comprehensive diagnostic criteria for IgG4-RD, which include IgG4 + cell count > 10/HPF and an IgG4 + /IgG ratio > 40%.

Results: Of the 19 cases, 2 were diagnosed as IgG4-AIH, with IgG4 + cell counts/HPF of 25.3 and 18.7, and IgG4 + /IgG ratios of 310.2% and 53.4%, respectively. Neither storiform fibrosis nor obliterative phlebitis was observed in the liver of these cases, and both responded excellently to corticosteroid treatment. In addition, from other 20 cases, we diagnosed 8 cases as IgG4-hepatopathy, with IgG4-SC and autoimmune pancreatitis being present in 7 and 2 cases, respectively.

Conclusions: This study identified two cases of IgG4-AIH and eight cases of IgG4-hepatopathy. Further studies are necessary to explore the occurrence of IgG4-AIH using these diagnostic criteria in the AIH cohort. The presence of IgG4-hepatopathy may facilitate the diagnosis of IgG4-SC.