Primary: papule on the penis → ulcerated painless chancre; resolves without treatment in 6-8 weeks (image A).
Secondary: maculopapular, annular, or hyperpigmented lesions, especially on palms and soles.
Tertiary: granulomas (gummas) that may involve the CNS.
Primary: dark-field microscopy or special stain reveals spirochetes (image B); lymphoplasmacytic vasculitis; antibody test is negative.
Secondary: organisms may or may not be seen; lymphoplasmacytic inflammation; antibody test is positive.
Tertiary: small compact granulomas that eventually caseate.