This stage can last for years, or even for decades. Late syphilis, the final stage, can result in mental illness, blindness, other neurologic problems, heart disease, and death. Syphilis bacteria frequently invade the nervous system during the early stages of infection, and approximately 3 to 7 percent of persons with untreated syphilis develop neurosyphilis. Some persons with neurosyphilis never develop any symptoms. Others may have headache, stiff neck, and fever that result from an inflammation of the lining of the brain.
Some patients develop seizures.
Patients whose blood vessels are affected may develop symptoms of stroke with resulting numbness, weakness, or visual complaints. In some instances, the time from infection to developing neurosyphilis may be up to 20 years. Neurosyphilis may be more difficult to treat and its course may be different in people with HIV infection. Sexually active people should consult a doctor about any suspicious rash or sore in the genital area. Those who have been treated for another STD, such as gonorrhea, should be tested to be sure they have not also acquired syphilis.