Primary syphilis is the first clinical stage of the sexually transmitted infection caused by Treponema pallidum, a spirochetal bacterial pathogen. A painless ulcer or chancre developing at the site of treponemal inoculation of the skin after intercourse, most commonly appearing on the penis, is the hallmark of primary syphilis. The diagnosis is made by clinical assessment and thorough laboratory studies that confirm the infection.
Syphilis, one of the most common sexually-transmitted infections (STD) worldwide, is caused by a spirochete, Treponema pallidum, and the clinical course of syphilis is divided into four stages - primary, secondary, latent, and tertiary    . Primary syphilis is the initial manifestation, characterized by the appearance of a painless papule eventually turning into an indurated ulcer on the skin or mucous membranes (known as the syphilitic chancre)    . The chancre is seen at the initial site of bacterial inoculation, and the diameter of the lesion ranges from a few millimeters up to a few centimeters without exudate, although secondary infection can produce a purulent discharge from the lesion  . Earlier syphilis occurred primarily in heterosexual men and women, however, now the incidence has increased amongst men having sex with men (MSM), with the glans penis being the most common site of the syphilitic chancre, usually after an incubation period of 10-90 days   . However, the lesion may appear at any site on the external genitalia, the anus, and perianal areas or in the oral cavity, and sometimes more than one chancre develops, especially in immunosuppressed individuals (such as those suffering from human immunodeficiency virus infection)   . Non-tender regional lymphadenopathy is often observed 1-2 weeks after the appearance of the typical skin lesion    . In most patients, chancres resolve spontaneously after approximately 3-6 weeks, but lymphadenopathy may be present much longer .
A detailed patient history and a proper physical examination can reveal sufficient data to make a presumptive diagnosis of syphilis in its primary stage. During the interview with the patient, physicians should assess sexual history, unprotected sex, multiple partners, etc.. and inspection and observation of typical skin lesions during physical examination could raise clinical suspicion. To confirm syphilis as the underlying cause, several diagnostic tests are available: