48. Diagnosis of syphilis

Syphilis diagnostic tests.

Dark field Microscopy: the lesion is cleansed and then abraded gently with a gauze pad. Once a serous exudate appears, it is collected on a glass slide and examined under a microscope equipped with a dark-field condenser. T. pallidum is identified by its characteristic corkscrew appearance.⁴ Given the inherent difficulties of dark-field microscopy, negative examinations on three different days are necessary before a lesion may be considered negative for T. pallidum.
Serological tests for syphilis: can be divided into –

Non-treponemal tests: blood test for diagnosis of infection with syphilis. Non-treponemal tests are an indirect method in that they detect biomarkers that are released during cellular damage that occurs from the syphilis spirochete (in easy words, they identify antibodies against phospholipids – mainly lectin and cardiolipin-which are produced during a syphilitic infection). Nontreponemal tests are screening tests, very rapid and relatively simple, but need to be confirmed by treponemal tests. Non – treponemal tests include the VDRL test (Venereal Disease Research Laboratory), the Rapid Plasma Reagin (RPR) and the unheated serum regain test (USR) and the toluidine red unheated serum test (TRUST).
Treponemal specific tests: these are tests that identify antibodies against Treponema Pallidum. These tests are used primarily to confirm the diagnosis of syphilis in patients with a reactive nontreponemal test. tests include the EIA for anti-treponemal IgG, the T. pallidum hemagglutination (TPHA) test, the micro-hemagglutination test with T. pallidum antigen, the fluorescent treponemal antibody-absorption test (FTA-abs), and the enzyme-linked immunosorbent assay. TPHA and FTA-abs are more frequently positive reactions and are more reliable.

Lumbar puncture: is required to establish the diagnosis of neurosyphilis. The CSF should be tested for white blood cell count and protein level, and for reactivity on a VDRL test. TPHA testing to compare serum and CSF values (TPHA index) may prove beneficial in establishing the diagnosis of neurosyphilis.