Rapidly progressive dementia (RPD) is an emergency in behavioural or cognitive neurology. Many rare neuroinfections like Neurosyphilis may be missed, if they are not thoroughly evaluated. We report a patient with subacute onset and progressive cognitive decline, extrapyramidal involvement and myoclonic jerks who was initially suspected as probable autoimmune encephalitis or Creutzfeldt-Jakob disease (CJD). Investigations revealed positive serum and cerebrospinal fluid (CSF) Venereal Disease Research Laboratory test (VDRL). On treatment with penicillin, he developed Jarisch-Herxheimer reaction and was treated symptomatically. After two weeks of penicillin, he improved significantly and except for mild short term memory recall, he is asymptomatic for last two years.