ESSENTIALS OF DIAGNOSIS
Painless ulcer on genitalia, perianal area, rectum, pharynx, tongue, lip, or elsewhere.
Fluid expressed from ulcer contains T pallidum by immunofluorescence or darkfield microscopy.
Nontender enlargement of regional lymph nodes.
Serologic nontreponemal and treponemal tests may be positive.
The typical lesion is the chancre at the site or sites of inoculation, most frequently located on the penis (Figure 34–1), labia, cervix, or anorectal region. Anorectal lesions are especially common among MSM. Chancres also occur occasionally in the oropharynx (lip, tongue, or tonsil) and rarely on the breast or finger or elsewhere. An initial small erosion appears 10–90 days (average, 3–4 weeks) after inoculation then rapidly develops into a painless superficial ulcer with a clean base and firm, indurated margins. This is associated with enlargement of regional lymph nodes, which are rubbery, discrete, and nontender. Bacterial infection of the chancre may occur and may cause pain. Healing of the chancre occurs without treatment, but a scar may form, especially with secondary bacterial infection. Multiple chancres may be present, particularly in HIV-positive patients. Although the “classic” ulcer of syphilis has been described as nontender, nonpurulent, and indurated, only 31% of patients have this triad.
Primary syphilis with a large chancre on the glans of the penis. The multiple small surrounding ulcers are part of the syphilis and not a second disease. (Used, with permission, from Richard P. Usatine, MD, in Usatine RP, Smith MA, Mayeaux EJ Jr, Chumley HS. The Color Atlas and Synopsis of Family Medicine, 3rd ed. McGraw-Hill, 2019.)
1. Microscopic examination
In early syphilis, darkfield microscopic examination by a skilled observer of fresh exudate from moist lesions or material aspirated from regional lymph nodes is up to 90% sensitive for diagnosis but is usually only available in select clinics that specialize in sexually transmitted infections. The darkfield examination requires expertise for proper specimen collection and identification of characteristic features of morphology and motility of pathogenic spirochetes, and repeated examinations may be necessary. Darkfield examination of oral lesions is not recommended because of the presence of nonpathogenic treponemes in the mouth. Spirochetes usually are not found in late syphilitic lesions by this technique.
An immunofluorescent staining technique for demonstrating T pallidum in dried smears of fluid taken from early syphilitic lesions is performed in only a few laboratories.
T pallidum polymerase chain reaction (PCR) is available in select research, referral, and public health laboratories and has the highest yield in primary and secondary lesions. Organisms can also be detected in blood, especially in congenital and secondary syphilis cases.
2. Serologic tests for syphilis