Histology shows wide variation in resurgent syphilis.

BALTIMORE -- Secondary syphilis does not always have the textbook lichenoid-psoriasiform appearance, said Dr. Timothy H. McCalmont, a professor of clinical pathology at the University of California, San Francisco.

"There's been a resurgence in syphilis. Keep it on your differential diagnosis short list," Dr. McCalmont said. "The microscopy of this disease is highly varied and the textbook descriptions that are out there are perhaps a little bit on the simplistic side," he said at the annual meeting of the American Society of Dermatopathology.

Dr. McCalmont and his colleagues reviewed their experience with syphilis, which included 23 specimens from 22 patients with a diagnosis confirmed by immunohistochemistry, polymerase chain reaction--based assay, or serology.

Histopathologically, most of the 23 samples did not demonstrate the textbook lichenoid-psoriasiform pattern. A lichenoid infiltrate was present in 11 of the specimens (48%), whereas psoriasiform epidermal hyperplasia was present in only 8 (35%). Clear involvement of the epidermal-dermal junction was found in 18 (78%); however, 5 (22%) showed wholly dermal involvement.

The dermal infiltrate included histiocytes in all specimens, neutrophils in 11 (48%), and plasmacytes in 22 (96%), however, plasmacytes were conspicuous in only 7 specimens (30%). Eosinophils are generally not found in syphilis, and none were found in any of these specimens. "If you see a juxtaposition of eosinophils and plasma cells, it's probably not syphilis," Dr. McCalmont said.

When using immunoperoxidase staining for Treponema pallidum, look for organisms at the perijunctional zone. "They often tend to have a coiled morphology that is easily picked up on staining," he said. The organism load is usually high.

Secondary syphilis can have a variety of patterns, Dr. McCalmont said. In addition to the lichenoid-psoriasiform pattern, granulomatous, sarcoidlike, and lupuslike patterns can be seen.