Syphilis

Syphilis is caused by the spirochete *Treponema pallidum*. After entering through skin or mucosa, it disseminates through the bloodstream and lymphatic system, so a localized lesion can be followed months or years later by systemic, neurologic, ocular, cardiovascular, or gummatous disease. Primary syphilis usually produces a chancre: a discrete, classically painless ulcer with a relatively clean base and regional lymphadenopathy. The lesion may be genital, anal, oral, or otherwise extragenital, and it can resolve without treatment. That apparent healing does not mean the infection has cleared. Secondary syphilis reflects systemic spread. A diffuse rash, including the palms and soles, generalized lymphadenopathy, mucous patches, fever, malaise, or condyloma lata should raise suspicion. The rash may be subtle or absent, and its appearance can resemble a viral exanthem, drug eruption, psoriasis, or pityriasis rosea. A painless ulcer favours syphilis over herpes simplex, which more often causes painful grouped vesicles or erosions, but pain alone cannot establish or exclude the diagnosis. Latent syphilis has positive serology without clinical findings. It is classified as early or late according to the time since infection; when...