IgG4-related disease]

IgG4-related disease is a recently recognized systemic syndrome characterized by mass-forming lesions, mainly in exocrine tissue, that consist of lymphoplasmacytic infiltrates and sclerosis. There are numerous IgG4+ plasma cells in the affected tissues, and the serum IgG4 level is elevated in these patients. Ocular adnexal IgG4-related disease frequently involves bilateral lacrimal glands, and obliterative phlebitis is rare. Moreover, some malignant lymphomas, especially mucosa-associated lymphoid tissue lymphoma, arise from ocular adnexal IgG4-related disease. It is known that hyper IL-6 syndromes, such as multicentric Castleman's disease, rheumatoid arthritis, and other autoimmune diseases, fulfill the histological diagnostic criteria for IgG4-related disease; therefore, hyper IL-6 syndromes and IgG4-related disease cannot be differentially diagnosed by immunohistochemical staining alone. However, upon laboratory examination, hype IL-6 syndromes show elevation of the CRP level, polyclonal hyper gamma-globulinemia, anemia, and hypoalbuminemia. These findings are quite different from IgG4-related disease, which is not characterized by elevated serum IgA, IgM, and CRP levels. Therefore, laboratory findings are crucial for the differential diagnosis.