ABSTRACT
Infectious mononucleosis(IM) is a benign self-limiting disease and result from a polyclonal B cell proliferation secondary to Epstein-Barr virus (EBV) infections. The infection is controlled by cytotoxic T cells triggered by EBV infected B cells. However, rare cases develop severe or fatal IM accompanied by hemophagocytic syndrome. We report a case of a 4-year-old girl who presented with high fever, hepatosplenomegaly, hepatic failure, pancytopenia and coagulopathy. Despite intensive treatment, the patient's condition deteriorated rapidly and died 3 days after admission. At autopsy, there was prominent infiltration of atypical lymphocytes with hemophagocytosis in multiple organs, especially liver, spleen and lymph nodes. Atypical lymphocytes were immunopositive for T cell markers and showed positive signal in EBV in situ hybridization.