FDG PET/CT findings in acute adult mononucleosis mimicking malignant lymphoma

We report a case of acute Epstein-Barr virus (EBV) infection in which the clinical syndrome and pattern of F-18-2-fluoro-2-deoxy-d-glucose (FDG) uptake mimicked malignant lymphoma. A 53-yr-old man presented with 2 wk of high fevers, night sweats, sinus congestion and severe fatigue. The patient was treated for 1 wk with broad-spectrum antibiotics for acute sinusitis without any improvement. Persistence of fevers and presence of abnormal lymphadenopathy seen on the abdominal computed tomography (CT) were concerning lymphoma with B symptoms. FDG positron emission tomography (PET) showed avid FDG uptake in numerous abdominal/pelvic nodes, liver, spleen and bone marrow. These findings were highly suspicious for lymphoma. Patient underwent a pelvic lymph node biopsy which showed large granular lymphocytes that were predominantly T cells. Bone marrow biopsy showed diffuse infiltration with plasmocytoid cells that were not kappa lambda restricted. Additional diagnostic workup became available showing positive EBV IgM titers and negative IgG levels indicating acute infectious mononucleosis. Lymph node biopsy stained positively with EBV-encoded RNA. We concluded that patient's abnormal FDG PET was most likely secondary to acute EBV infection. After 2 months, follow-up FDG PET/CT showed marked improvement in lymphadenopathy and decreased hypermetabolic activity in the liver and spleen. Other than EBV, there are many other FDG-avid non-malignant conditions that may lead to false-positive PET scans. FDG accumulates in inflamed and infected lesions with increased glucose metabolism. This case underscores the importance of maintaining a broad differential and restricting use of PET scans for staging.