Background: Syphilitic chancre could be misdiagnosed as other skin diseases and a biopsy is sometimes done before serological testing, which makes it essential to find possible primary syphilis patients through histopathology and immunohistochemistry (IHC).
Method: We sought to determine the histopathological and IHC characteristics in primary syphilis. Eleven biopsy specimens were collected from 9 patients diagnosed with primary syphilis. Specimens were analyzed for T. pallidum using antibody to T. pallidum. We also compared IHC results with the histological characteristics.
Results: In our study, plasma cells infiltration was the most common pattern [90.9% (10/11)] in primary syphilis. Necrotic keratinocytes could be observed in 54.5% (6/11) of primary syphilis. T. pallidum was discovered in 9 of 10 (90.0%) primary syphilis by IHC. T. pallidum is mainly detected in the medium to superficial dermis and the lower epidermis regions. In the dermis area, T. pallidum was discovered mainly around the perivascular regions.
Conclusion: Although serological tests remain the gold standard for the confirming diagnosis of syphilis infection, Histopathological and IHC could be helpful in the diagnosis of some syphilitic patients when serologic testing is not capable of detecting T. pallidum antibodies in serum. Using IHC technique allows us to precisely find out the location of the microorganism in the syphilitic skin lesions.