Lymphadenopathy of IgG4-related disease: an underdiagnosed and overdiagnosed entity.

Lymphadenopathy is a common occurrence in IgG4-related disease; it can appear before, concurrent with, or after the diagnosis of this disease, which is characterized by tumefactive sclerosing inflammatory lesions predominantly affecting extranodal sites, such as the pancreas, salivary gland, and lacrimal gland. Although multiple lymph node groups are commonly involved, constitutional symptoms are absent. The lymph nodes can show a broad morphologic spectrum, including multicentric Castleman disease-like (type I), follicular hyperplasia (type II), interfollicular expansion (type III), progressive transformation of germinal centers (type IV), and inflammatory pseudotumor-like (type V). All are characterized by an increase in IgG4+ plasma cells (>100 per high power field) and IgG4/IgG ratio (>40%). IgG4-related lymphadenopathy is both an underdiagnosed and overdiagnosed entity. The former is because of the fact that this entity has not been characterized until recently, while the latter results from pathologists' enthusiasm in diagnosing "new" entities and the lack of specificity of the morphologic and immunophenotypic features of IgG4-related lymphadenopathy. It is prudent to render this diagnosis only for patients with known IgG4-related disease or in the presence of corroborating clinical and laboratory findings (such as elderly men, systemic lymphadenopathy, elevated serum IgG4, IgG, and IgE but not IgM and IgA, and low titers of autoantibodies). Outside these circumstances, a descriptive diagnosis of "reactive lymphoid hyperplasia with increased IgG4+ cells" accompanied by a recommendation for follow-up will be appropriate because IgG4-related disease will likely ensue only in a minority of such patients.