Primary Oral Syphilis, a Diagnostic Challenge and the Mimicry of Indolent Lesions: Case Report

Syphilis, an infection caused by Treponema pallidum, remains one of the main sexually transmitted infections in Brazil, with rising incidence in recent years. Oral manifestations, although less frequent than genital ones, may pose a diagnostic challenge due to their clinical diversity and similarity to other conditions. The aim of this report is to describe an atypical case of primary oral syphilis, initially interpreted as an aphthous ulcer refractory to corticosteroid therapy. Male, 51 years old, with a 2-month history of a 4-mm ulcerated lesion on the left lower lip, without associated systemic symptoms. The ulcer was painless, aphthous, bullous, and had initially been treated with corticosteroids without regression. Rapid tests for syphilis and HIV were performed and both were nonreactive, while VDRL was reactive at 1:32. Biopsy of the ulcer showed a chronic subepithelial and deep perivascular inflammatory process, predominantly lymphoplasmacytic, with epithelial hyperplasia associated with parakeratosis and exocytosis. Clinical, histopathological, and immunohistochemical findings were compatible with primary oral syphilis. Oral manifestations of syphilis are less prevalent and often underdiagnosed. Typical primary oral syphilitic chancre presents as a solitary, painless ulcer with an indurated base, clean non-purulent bed, and well-defined margins, commonly located on the lip or tongue. These presentations represent a considerable diagnostic challenge, given their similarity to multiple oral conditions. In secondary syphilis, oral lesions may include irregular whitish mucous plaques, painful aphthous-like ulcers, and maculopapular rash (syphilitic rosette), often associated with systemic symptoms such as pharyngitis. In the context of increasing global and national incidence, it is important to include syphilis in the differential diagnosis of persistent oral lesions and to perform serologic testing and, when indicated, lesion biopsy. In the present case, biopsy was essential for definitive diagnosis, especially in view of the initial discordant serologic results. Appropriate diagnosis and treatment are crucial for clinical resolution and interruption of the transmission chain.