Serological diagnosis of secondary syphilis in a Rituximab‐treated patient: an emerging diagnostic challenge?

The secondary syphilis (SS) is usually characterized by cutaneous eruptions sometimes atypical associated with unspecific symptoms.1 Serology is normally highly positive and reliable in diagnosis of SS.2 However, some issues of serological diagnosis have already been reported previously in human immunodeficiency virus-infected (HIV) patients.3 Here, we present an uncommon case of SS in a 33-year-old man treated with Rituximab (RTX) (for multiple sclerosis with last injection in May 2019) whose treponemal test (TT) was initially non-reactive even though a typical rash was observed since more than 12 days before. Despite inconclusive serological assays for syphilis, we suggested SS and the patient received three injections of benzathine penicillin (2.4 million units intramuscular weekly) with a dramatic improvement after the first injection. Physicians caring for RTX recipients or severe immunocompromised patients should be aware that some patients may present symptoms of SS with initial negative serology. [Extracted from the article]