Reactive lymphadenopathies that mimic lymphoma: entities of unknown etiology.

Kikuchi-Fujimoto disease, Kimura disease, Rosai-Dorfman disease and IgG4 related lymphadenopathy may present with enlarging masses clinically mimicking lymphoma. A combination of clinical and histologic findings is necessary to diagnose these important rare entities, which may occasionally have aggressive clinical behavior. The recognition of these disorders is important in order to avoid misdiagnosis of malignancy, other systemic diseases such as systemic lupus, and to institute correct management and therapy, such as steroid treatment for IgG4 related lymphadenopathy. The underlying etiologies of these diseases are not completely clear at present, however, their recognition has become more common as diagnostic techniques improve. Their diagnosis and recognition may help to elucidate their underlying pathobiology.