Three cases of infectious mononucleosis with concurrent false-positive non-treponemal and treponemal tests: Serological findings masquerading as syphilis.

Biological false-positive reactions to non-treponemal syphilis tests occur under various conditions, including in patients with infectious mononucleosis. However, false-positive treponemal test results are rarely reported. We present three cases of Epstein-Barr virus-associated infectious mononucleosis that exhibited concurrent false-positive results in both treponemal and non-treponemal tests, effectively imitating syphilis serology. Notably, the false-positive treponemal test results were transient and persisted for more than 6 months before reverting to negative. This is atypical for true Treponema pallidum infection (syphilis), in which treponemal tests usually remain positive for life. This case series highlights the potential for misdiagnosis and emphasizes the importance of careful interpretation of syphilis serology results in the context of infectious mononucleosis. This is particularly important when typical syphilis symptoms are absent, as in our patients. The similarity in the clinical manifestations between infectious mononucleosis and syphilis, including sore throat, lymphadenopathy, rash, and hepatitis, further complicates the diagnostic process. Clinicians should consider recent Epstein-Barr virus-associated infectious mononucleosis when interpreting positive syphilis serology, especially in young adults presenting with mononucleosis-like symptoms. Follow-up serological testing is useful to avoid unnecessary treatment and potential patient mismanagement.