This is a somewhat unusual case of syphilis, as it is more granulomatous than the textbook example. Typically, one would see a psoriasiform hyperplasia with numerous plasma cells. The histiocytic component may represent a late secondary moving to tertiary (gummatous) phase. When there is a mixed pattern with plasma cells and granulomas, one must always think of syphilis. This disease is prevalent in Dallas, although usually presents in the STD clinic and is not biopsied. One can pick up the treponemes using a silver stain (Warthin-Starry or Steiner) or a immunohistochemical stain, as in this case. We happen to have a good immunohistochemical stain for t. pallidum.
There is a predominantly dermal infiltrate, extending deep into the biopsy in a vaguely perivascular pattern. The epidermis is only mildly acanthotic.