Abstract

Immunohistochemical staining (IHC) for spirochetes in skin specimens can be used for diagnosing secondary syphilis; however, limited data are available to assess its efficacy against standard serology testing. In our study, 175 patients with biopsies that underwent spirochete IHC from January 1, 2014 to December 31, 2022 were identified in a private practice setting. Those patients who did not have an adjacent Rapid Plasma Reagin (RPR) test or underwent spirochete immunostaining for other diseases were excluded. The final cohort consisted of 26 patients, of which 17 (65%) were male with an average age of 42.54 ± 13.39 years.  With serology as the “gold standard,” IHC showed sensitivity of 80.00%, specificity of 90.48%, positive predictive value of 66.67%, and negative predictive value of 95.00%. Given its high sensitivity and specificity, our study supports Treponema pallidum immunostaining as a valid method for detecting secondary syphilis, even in cases when serology studies (i.e. RPR) are not available.