Orbital Mass With Features of Both Kimura Disease and Immunoglobulin G4-Related Disease

Kimura disease has been known as a chronic inflammatory disease of unknown etiology, since the first report in 1937 and characterized by an increased eosinophil fraction in peripheral blood, increased serum immunoglobulin E (IgE) levels, and lymphoid granuloma with eosinophilic infiltration on histopathological examination. The authors present a 30-year-old man who visited their clinic with a 3-month history of protrusion and conjunctival injection of the right eye. Surgical mass resection was performed, and initial histopathology revealed Kimura disease. Additional immunohistochemical examination revealed IgG4-related disease in another hospital, which showed more than 80 IgG4-positive plasma cells per high-power field and an IgG4+/IgG+ ratio more than 40%. There are histopathological similarities, and several reports have suggested a relationship between Kimura disease and IgG4-related disease. Thus, it is difficult to classify them as completely different diseases. Kimura disease and IgG4 can be considered a part of a clinical spectrum of abnormal immune reactions.