Fever of unknown origin (FUO) in an elderly adult due to Epstein-Barr virus (EBV) presenting as "typhoidal mononucleosis," mimicking a lymphoma.

We describe fever of unknown origin (FUO) in a 57-year-old woman with hepatosplenomegaly. The diagnostic workup was directed at diagnosing a lymphoma. Her history of travel and exposures to food and water did not make typhoid fever a likely diagnostic possibility. Because she presented with prolonged fevers, fatigue, anorexia, weight loss, and night sweats with hepatosplenomegaly, lymphoma was likely. Initially, Epstein-Barr virus (EBV) was not considered because of her age, the absence of pharyngitis and cervical adenopathy, and the higher likelihood of another diagnosis, ie, lymphoma. Eventually, her FUO was diagnosed as EBV presenting as "typhoidal mononucleosis." Typhoidal mononucleosis is an extremely rare presentation of EBV as a cause of FUO in an adult. All of her symptoms as well as her clinical and laboratory findings resolved spontaneously.