Syphilis causes symptoms that are very similar to those of many other diseases and are sometimes not recognized. Syphilis has historically been referred to as "the great imitator."

Symptoms of the primary stage of syphilis are similar to those of:

• Other sexually transmitted infections. Examples include:
  • Chancroid.
  • Herpes simplex virus.
• Any bacterial infection that causes open sores.

Symptoms of the secondary stage of syphilis are similar to:

• A syndrome that causes eruptions of the skin and mucous membranes (erythema multiforme).
• A type of skin inflammation that causes itching and large patches of scaly skin sores (psoriasis) or a type of psoriasis that is painless.
• A skin rash caused by a viral infection or from being bitten by a tick (Rocky Mountain spotted fever or Lyme disease).
• A condition called pityriasis rosea that causes a slightly scaling, pink, raised rash over the trunk and unexposed areas of the body.
• A skin disease caused by the bites of insects, such as mites (scabies).
• Initial infection with the human immunodeficiency virus (HIV).
• A condition in which the blood vessels in the anus become inflamed and sore (hemorrhoids).
• Cancer of the lymph system (lymphoma).
• A disorder that causes body tissues to thicken (sarcoidosis).
• Lupus, which can cause a skin rash, joint pains, and other symptoms.
• Some types of genital warts, especially when they occur around the anus.

Symptoms of the tertiary (late) stage depend on the organ system affected. Symptoms may resemble those of:

• Advanced HIV infection.
• AIDS-related dementia.
• Alzheimer's disease.
• Stroke.
• Dementia, which is a progressive decline in a person's mental abilities.
• Degenerative diseases of the brain and spinal cord (central nervous system).
• Coronary artery disease or valvular heart disease.

Symptoms of syphilis that are present at birth (congenital syphilis) may be similar to:

• German measles (rubella).
• A herpes-type virus that causes serious illness in newborns (cytomegalovirus).
• A skin disease that causes sores, usually in the mouth and nose (impetigo).