Atypical presentation of syphilis as an aphthous ulcer

A 28-year-old nulliparous woman presented to an ambulatory outpatient clinic with a one-month history of a nonhealing aphthous ulcer on her inner lower lip that initially caused mild discomfort when eating. Saline rinses and a corticosteroid oral gel were ineffective. She had unprotected oral and vaginal sex on one occasion with a male partner one month before symptom onset. She did not have any genitourinary or constitutional symptoms, and did not smoke. She had not been immunized with recombinant human papillomavirus quadrivalent vaccine. Upon clinical examination, she had a nontender, firm, well-circumscribed, skin-colored round macule with a rolled border on the mucosal membrane of the lower lip, without evidence of lymphadenopathy. The differential diagnosis included syphilitic chancre, oral herpes simplex virus and malignant disease. Management of primary syphilis includes first-line treatment with benzathine penicillin, testing for sexually transmitted infections and sexual abstinence pending resolution of symptoms after treatment.