Background: The incidence of syphilis has increased in high-income countries in the past few decades, especially among men who have sex with men. In the present study, we aimed to analyze the correlations between atypical syphilis manifestations and the demographic, clinical, and laboratory features of patients and to review unusual presentations of syphilis reported in the literature. Methods: We conducted a retrospective analysis of 307 patients with syphilis diagnosed between 1 January 2013 and 31 October 2023 at the sexually transmitted infection (STI) centers of the University of Genoa and University of Foggia with both typical and atypical manifestations of disease. Results: In our series, atypical manifestations were detected in 25.8% of the patients, especially in the secondary stage of the disease. Lesions with annular morphology and lesions presenting as itchy erythematous scaly plaques with a psoriasiform appearance were the most common atypical presentations of secondary syphilis. A statistical analysis revealed that homosexual orientation, syphilis reinfection, and venereal disease research laboratory (VDRL) titers > 1:32 were correlated with atypical manifestations. Conclusions: Our study demonstrates that the spectrum of syphilis manifestations, in all the stages of the disease, is wide; atypical manifestations often pose diagnostic challenges, may delay the provision of appropriate treatment, and facilitate the spread of the infection.

Syphilis is a sexually transmitted infection caused by Treponema pallidum. The primary stage of the disease manifests as a chancre. Balanoposthitis as a presenting feature of primary syphilis is a very rare presentation. A 26-year-old male presented with asymptomatic erythematous plaques involving the glans and prepuce after unprotected intercourse with a known female. Routine investigations, serology, and dark field examination were normal. Fontana-Masson stain revealed spirochetes and a diagnosis of syphilitic balanitis of Follmann was entertained. This rare presentation accounts for only 0.3%-0.5% of cases of primary syphilis and hence is highlighted in this case report.

Syphilitic balanitis of Follmann (FB) is a rarely described manifestation of primary syphilis that was first reported in 1948. Its clinical appearance may be heterogeneous varying from painful edematous balanoposthitis to superficial erosive balanitis and asymptomatic glans induration. We described a patient presenting with FB, as manifestation of primary syphilis, and concurrent anetoderma, as manifestation of secondary syphilis. The association of these lesions was never described to date.