Dory Flop Sign of Syphilis

Syphilis is a sexually transmitted disease caused by the bacterium Treponema pallidum variant pallidum. Incidence of primary and secondary syphilis in the United States increased each year from 2000 (2.1 cases per 100 000 persons) to 2008 (4.5 cases per 100 000 persons).¹ In 2008, 13 500 primary and secondary syphilis cases were reported in the United States,¹ and each year an estimated 12 million syphilis cases occur worldwide.² Early diagnosis and prompt treatment of syphilis can benefit both individual patients and public health prevention and control efforts.³

A 27-year-old man presented with a painless lesion of 3 weeks' duration on the prepuce. He had 2 female sex partners during the prior 3 months and was not HIV infected. Physical examination showed a nontender indurated ulcer on the prepuce, to the left of the frenulum, and a nontender papule with a collarette of scale on the penile shaft (Figure). As the patient retracted the prepuce, it did not roll back smoothly but, in the area where the chancre was present, tipped up slowly and then flipped over all at once. That movement mimics the movement of a dory, a small, flat-bottomed fishing boat, which flips over all at once when overturned (video). A darkfield microscopy examination of material obtained from the ulcer showed motile spirochetes. A rapid plasma reagin test was reactive (1:16 titer), as was a T pallidum particle agglutination test. The patient received 1 intramuscular dose of 2.4 million U of benzathine penicillin G.

The sign exhibited by the movement of this patient's prepuce on retraction is called the dory flop sign.⁴ The sign, named by the dermatologist and syphilologist John Stokes, refers to the motion of a dory, a small, flat-bottomed, wooden fishing boat, which flips over all at once when overturned.^{4 - 5} The sudden flip of the prepuce on retraction in the presence of a syphilitic chancre reflects the induration of the skin where the chancre is present; in that area, the skin loses its elastic quality and therefore cannot retract smoothly. The sign is suggestive of, although not diagnostic for, syphilitic chancres,⁵ which typically are more indurated than other causes of preputial ulcers. Another clue to the diagnosis in this case is the location of the ulcer, which was adjacent to the frenulum, a common location for syphilitic chancres.⁴ Recognition of the dory flop sign can contribute to early diagnosis and treatment, and hence prevention and control, of syphilis.

Correspondence: Dr Katz, County of San Diego, HIV, STD, and Hepatitis Branch, Health and Human Services Agency, 3851 Rosecrans St, Ste 207, San Diego, CA 92110 (kenneth.katz@sdcounty.ca.gov).

Financial Disclosure: Dr Katz has received an honorarium from Stiefel Inc and serves on the editorial board of VisualDx.com.