Clinicopathological differential diagnosis of IgG4‐related disease: A historical overview and a proposal of the criteria for excluding mimickers of IgG4‐related disease

IgG4‐related disease (RD) is a relatively new entity, which was first proposed in 2001. Since then, clinical and pathological characteristics of the disease have been investigated. As IgG4‐RD has been studied extensively, the diagnostic criteria for IgG4‐RD of each organ and the comprehensive diagnostic criteria for IgG4‐RD have also been developed. However, one of the biggest challenges in the field is distinguishing between IgG4‐RD and mimickers, which show overlapping features with IgG4‐RD. It is now known that some non‐IgG4‐RDs may meet the diagnostic criteria of IgG4‐RD and can be misdiagnosed as IgG4‐RD. However, accurate diagnosis is crucial, as the treatments for IgG4‐RD and those for other diseases that may be misdiagnosed as IgG4‐RD are different. This prompted us to create and propose comprehensive exclusion criteria for IgG4‐RD. In this review, we have described the comprehensive exclusion criteria for IgG4‐RD, with a historical overview of the disease. These exclusion criteria were recently created by the Research Program for Intractable Disease of the Ministry of Health, Labor, and Welfare of Japan, All Japan IgG4 team, to support correct and accurate diagnosis of IgG4‐RD.