Detection of Treponema pallidum in the Skin Lesions of Primary and Secondary Syphilis: An Immunohistochemical Study

Background: Syphilis is an infection caused by Treponema pallidum (T. pallidum), and this disease is increasing in incidence. However, making the diagnosis of syphilis is sometimes still challenging because of the variable clinical and histopathologic findings and there are cases with negative serologic findings, and especially in the setting of HIV infection and immunosuppressive therapy.Objective: In this study, we specifically evaluated the number and distribution patterns of T. pallidum in the skin lesions from patients with primary or secondary syphilis.Methods: Forty eight skin biopsy specimens with the clinical and/or serological diagnosis of syphilis were evaluated by immunohistochemistry (IHC) using primary polyclonal antibodies against T. pallidum.Results: Overall, T. pallidum was identified in 45 specimens (94%). The IHC of the 22 specimens from the patients with primary syphilis were all positive (100%). Twenty three (88%) out of 26 specimens from the patients with secondary syphilis showed positive results. T. pallidum was also identified in three patients with negative VDRL. Although the density of T. pallidum was higher in the specimens from the patients with primary syphilis than in those from the patients with secondary syphilis, the differences were not statistically significant (p=0.32). An epitheliotropic pattern was more frequently observed in the specimens from the patients with secondary syphilis (81%) than in those from the patients with primary syphilis (50%) (p=0.01). The density and distribution patterns of T. pallidum didn’t show any correlation with the duration of skin lesions or the VDRL titer.Conclusion: IHC using a polyclonal antibody against T. pallidum could be an effective method for making the diagnosis of primary and secondary syphilis. (Korean J Dermatol 2010;48(10):844∼852)Key Words: Immunohistochemistry, Polyclonal antibody, Syphilis, Treponema pallidum서 론