Toxoplasma IgG expressed in a patient with Rosai-Dorfman disease.

Rosai-Dorfman Disease (RDD) is a rare benign disease characterized by sinus histiocytosis with massive lymphadenopathy. RDD can be differentiated from other types of histiocytosis by immunochemical analysis, as RDD is positive for S100. Conversely, toxoplasmosis lymphadenitis is characterized by clusters of epithelioid histiocytes in lymphoid tissue, with mixed lymphocytic and immunoblastic cell populations. The serology data could help in diagnosing toxoplasmosis lymphadenitis, as the toxoplasma IgG should be positive. Here we present the rare case of a 73-year-old woman who presented with a left parotid mass and multiple neck lymphadenopathy that initially had been diagnosed as toxoplasmosis lymphadenitis from a positive result on serology examination, but was finally proven to be RDD based on immunochemical results. We also discuss the relationship between RDD and toxoplasmosis in this case.