False-negative anti-treponemal immunohistochemistry in secondary syphilis

Background While serological studies are the primary tool used to confirm the diagnosis of secondary syphilis, skin biopsies are often performed to control for potential false positives and negatives. Immunohistochemistry using anti-T.similar to pallidum specific antibodies has proven to have a very high sensitivity and specificity for identification of spirochetes in biopsy specimens, but can occasionally fail to identify organisms in clinically and serologically confirmed cases. Methods We report two cases of apparently negative biopsy specimens in which rare organisms were subsequently identified by detailed study of multiple additional sections. Results Our experience suggests that the sensitivity of immunohistochemistry for syphilitic spirochetes may be improved by repeat immunostaining.