22. FDG Uptake in Infectious Mononucleosis

Background: As the role of PET-FDG imaging is being established in the staging and monitoring of response to therapy in children with lymphoma, we encountered a case of an infection common in adolescence that may present with lymphoma-like signs and symptoms.Methods: A 13-year-old previously healthy male presented with a left neck mass associated with weakness, fatigue, intermittent fevers and weight loss. He was then referred to the hematology/oncology department with a working diagnosis of lymphoma. The total wbc count was 5920/cu mm with 75% lymphocytosis without atypical lymphocytes. ESR was 20 mm. Serologic analysis for EBV, CMV, toxoplasmosis and hepatitis was also performed. The chest x-ray was normal. CT scan demonstrated multiple enlarged lymph nodes in both right and left jugulodigastric and spinal accessory chains; the largest mass within the left spinal accessory chain had focal necrosis within it. There were no enlarged mediastinal or axillary nodes. The spleen was massively enlarged and the splenic index was 924 (normal for age = 744).Results: FDG imaging showed intense uptake in both cervical regions, the mediastinum and in the enlarged spleen. The results of the Monospot test and the EBV panel which were both positive, were available 3 & 5 days later. Based on these serologic results, the history, physical findings and the negative chest x-ray, the final diagnosis was infectious mononucleosis.Conclusion: Despite availability, ease of performance and sensitivity of FDG imaging, this case illustrates the importance of clinical, hematologic and serologic assessment of disease prior to FDG imaging.