Large granules in the peripheral blood smear and bone marrow aspirate of a 3-year-old male with lymphadenopathy and fever.

A 3-year-old male with oculocutaneous albinism presented with lymphadenopathy and fever. Serological testing revealed Epstein-Barr virus (EBV)-specific immunoglobulin M (IgM) and a diagnosis of infectious mononucleosis was made. A complete blood count and peripheral blood smear demonstrated mild anemia, thrombocytopenia, and neutropenia with leukocytes that contained large azurophilic and eosinophilic granules. Bone marrow examination demonstrated increased hemophagocytic histiocytes along with granulocytes that contained large eosinophilic granules. In addition to hemophagocytic lymphohistiocytosis, presumably due to acute EBV infection, the patient was diagnosed with Chediak-Higashi syndrome based on the pathognomonic granules within peripheral leukocytes and precursors. The differential diagnosis of a young patient with oculocutaneous albinism presenting with an acute viral infection includes a relatively narrow range of genetic syndromes based solely on the history of albinism. This case demonstrates the application of clinical laboratory data to presumptively diagnose Chediak-Higashi syndrome in the midst of a presentation of hemophagocytic lymphohistiocytosis secondary to acute EBV infection.