IgG4-related lymphadenopathy: a potentially under- and over-diagnosed entity.

IgG4-related lymphadenopathy (IgG4-LAD) is newly described entity, which may occur before, during or after diagnosis of extranodal IgG4-related disease. It is important to recognize IgG4-LAD, especially in cases with lymphadenopathy as the initial presentation, so that the patients can receive prompt treatment. However, it can be challenging to formulate a final diagnosis since IgG4-LAD displays a broad morphologic spectrum. Moreover, morphologic changes alone are not sufficient for diagnosis of IgG4-LAD, and an accurate diagnosis has to take into account of the overall clinical presentations and laboratory studies. Currently, it is not very clear when pathologists should consider workup for potential IgG4-LAD based on the histologic features. Particularly, for some pathologists, it is not certain how to render the diagnosis in reactive lymph nodes with markedly increased IgG4 + cells. In this review, we will attempt to summarize the major clinicopathologic features of IgG4-LAD and its variants, differential diagnoses, and algorithms to establish an accurate diagnosis.