Syphilis makes you go mad, is that true?

It still does: About a third of people with untreated syphilis eventually suffer brain damage, and this often takes the form of general paresis, a horrific brain disease with bizarre behavior progressing to dementia. If you have any concern that you may be carrying syphilis, please get seen -- it still happens today.

Yes: Neurosyphilis (tertiary phase)can present as delirium, dementia, mania, paranoia, personality changes, cognitive changes or psychosis. Encephalitis can present in the quaternary phase.