IgG4-related disease is a reactive lymphoproliferative-sclerosing lesion that can involve various organ systems of the body, with autoimmune pancreatitis being the prototype. This review article focuses on the various lymphoproliferative lesions that can occur in this disease. The first is IgG4-related lymphadenopathy, which can accompany typical IgG4-related disease or occur ab initio. The morphologic spectrum of the affected lymph nodes ranges from multicentric Castleman disease-like, to follicular hyperplasia, marked interfollicular expansion mimicking peripheral T-cell lymphoma, progressive transformation of germinal center-like, and nodal inflammatory pseudotumor-like. The diagnosis can be confirmed by demonstration of an increase in IgG4+ plasma cells. The second is the development of lymphoma in patients with IgG4-related disease. The lymphoma can occur in the sites affected by IgG4-related disease, where the most common type is extranodal marginal zone lymphoma; or in other nodal and extranodal sites, where the most common type is diffuse large B-cell lymphoma. The third is florid lymphoid hyperplasia as the dominant morphologic feature of IgG4-related disease in various extranodal sites, mimicking malignant lymphoma. Such findings appear to be particularly common in the salivary gland, lacrimal gland, skin and breast, probably attributable to early discovery of mass lesions involving these sites, before the sclerosing process has time to take over.
Keywords: IgG4-related disease, IgG4-related sclerosing disease, lymphoproliferative lesion, pseudolymphoma, lymph node pathology, lymphadenopathy, lymphoma, florid lymphoid hyperplasia, follicular hyperplasia, Castleman disease-like
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