This stage can last for years, or even for decades. Late syphilis, the final stage, can result in mental illness, blindness, other neurological problems, heart disease, and death. The syphilis bacterium frequently invades the nervous system during the early stages of infection, and approximately 3-7 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 persons develop seizures.
In those whose blood vessels are affected, symptoms of stroke can occur with resulting numbness, weakness, or visual complaints. In some instances, the time from infection to the development of 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. People who have more than one sex partner 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.