Case Presentation:

A 42–year–old man who works for the Justice Department stationed in Ghana presented with 3 days history of headache, fatigue fever (105°F) and sore throat. He was treated with anti–malarial and antibiotics. Few weeks later, fever continues with drenching sweats and was flown to the US for further work up. On presentation to our hospital he was afebrile, few small submental lymphadenopathy, oral thrush and papular rash on his back. Laboratory findings were significant for WBC 3.0 k/uL, absolute neutrophil count (ANC) 0, hemoglobin 12.9 g/dL, platelets 587 k/uL, normal electrolytes, and elevated CRP 12.2. Peripheral blood smear showed many large granular lymphocytes and 19% LGL on flow cytometry. He had elevated EBV–IgG >8 AI (normal < 0.9AI) and EBV DNA – 941 copies/mL. Malaria smear, ANA, CMV, respiratory and blood cultures, HIV, HTLV, fungal battery, Parvovirus, HHV6, Toxoplasmosis, S. Typhi, RF, reticulocytes, LDH were all within normal limits. CT scan revealed small prominent reactive cervical lymphadenopathy. Bone marrow biopsy showsed normocellularity, granulocytic hyperplasia with left shift. Three months later, he continues to be asymptomatic with normal blood smear with no evidence of atypical lymphocytes. Repeat bone marrow biopsy showed decline in LGL cells. The diagnosis of atypical infectious mononucleosis was entertained due to spontaneous recovery of symptoms, neutropenia, LGL cells and nonspecific LGL leukemia type.


Neutropenia and increased LGL levels is a rare presentation of infectious mononucleosis which mimics LGL leukemia. LGL is an uncommon type of leukemia that has few subtypes, some with rapid deterioration. The diagnosis of LGL leukemia is based on the presence of an LGL lymphocytosis, characteristic immunophenotype, and confirmation of clonality using TCR gene rearrangement studies. Reactive LGL lymphocytosis can be seen in viral infections but the differentiation between reactive and true LGL leukemia can be challenging. In most reported cases of atypical infectious mononucleosis there is no evidence of T–cell monoclonality. To our knowledge, this is a unique case of infectious mononucleosis with mild expansion of TCR–VB14. In this case, given the spontaneous recovery and the unusual immunophenotype expression lead to the diagnosis of Infectious mononucleosis.


Hospitalists have to be vigilant about recognizing patients presenting with fever sore throat and neutropenia. Infectious mononucleosis (IM) is a, self–limiting disease caused by Epstein–Barr virus (EBV). Patients usually present with malaise, fatigue, fever, lymphadenopathy and pharyngitis. IM can cause a reactive proliferation of lymphocytes that could mimic large granulocytic lymphocyte (LGL) leukemia. We report a case of atypical IM with absolute neutropenia, LGL lymphocytosis simulating LGL leukemia.