Neurosyphilis Is a Long-forgotten Disease but Still a Possible Etiology for Dementia.

We herein report a heterosexual Japanese man in his forties who had been suffering from advanced dementia and personality change for 4 years. Positive results of a serological test for syphilis, Treponema pallidum hemagglutination assay, and fluorescent treponemal antibody-absorption test of both serum and cerebral spinal fluid led to the diagnosis of neurosyphilis. Jarisch-Herxheimer reaction was seen shortly after the first dose of penicillin was administered to the patient. His cognitive function did not recover after treatment. The incidence of syphilis has been reported to be increasing. Neurosyphilis should not be overlooked as an etiology for progressive dementia even in this post-antibiotic era.