Infectious mononucleosis with atypical manifestations accompanied by transient IgM antibody response for cytomegalovirus.

Infectious mononucleosis (IM) is a clinical syndrome caused by primary infection with Epstein-Barr virus (EBV) that is common in adolescents. In adults, particularly in elderly people, the clinical picture of IM tends to be atypical, often leading to a diagnostic challenge. Diagnosis is also complicated because infection with EBV can induce the synthesis of cross-reacting immunoglobulin M antibodies for other herpesviruses. We report an unusual case of infectious mononucleosis in a 34-year-old immunocompetent adult. Epidemiological studies indicate that the average age of primary EBV infection in developed countries is increasing. IM with atypical presentation will be a diagnostic challenge in the future as the number of EBV-naïve adults increases.