Atypical lymphoid hyperplasia mimicking lymphoma.

The distinction between reactive and neoplastic lymphoid infiltrates is a common problem in clinical practice and can be problematic. The clinical implications for both the patient and the treating clinician are profound. In this article, we discuss six of the common entities that can present as atypical lymphoid hyperplasia and thus can mimic malignant lymphomas, with emphasis on morphologic features, immunophenotypic findings, and molecular correlates that help distinguish these disorders from neoplastic conditions. The six conditions to be discussed in detail include reactive follicular hyperplasia versus follicular lymphoma; progressive transformation of germinal centers versus nodular lymphocyte predominant Hodgkin lymphoma; immunoblastic proliferations versus diffuse large B-cell lymphomas; variant forms of Castleman disease that may mimic a number of lymphoid cancers; Kikuchi's disease versus large cell lymphomas; and finally, dermatopathic lymphadenopathy and its distinction from lymph nodes showing early involvement by cutaneous T-cell lymphoma (Mycosis fungoides).