Primary syphilis (genital ulcer)

• Herpes simplex virus (HSV)
• Chancroid
• Granuloma inguinale
• Lymphogranuloma venereum
• Trauma
• Neoplasm
• Behçet’s syndrome
• Systemic lupus erythematosus (SLE)
• Lichen planus

Secondary syphilis (rash, condyloma lata, lymphadenopathy)

• Rash: pityriasis rosea, tinea corporis, psoriasis, nummular eczema, viral exanthem, drug eruption, lichen planus, discoid lupus erythematosus
• Condyloma lata: genital warts (condyloma acuminata), vulvar cancer

Tertiary syphilis (neurosyphilis, cardiovascular, gummas)

• Gummas: skin cancer; lipomas; sarcoidosis; ulcer due to pyoderma gangrenosum, vasculitis, mycobacterial infection, deep fungal infection, yaws
• Aortic root disease: Marfan syndrome, aortic dissection, temporal (giant cell) arteritis, ankylosing spondylitis, syphilis, Reiter’s syndrome (reactive arthritis), cystic medial necrosis, sinus of Valsalva aneurysm, relapsing polychondritis
• Neurosyphilis: primary neurologic lesions or other chronic meningitis