Neurosyphilis Presenting as Rapid Cognitive Decline With Demonstrated Improvement Posttreatment: A Case Report

Syphilis has become an increasing public health concern in recent times, with rising incidence globally. It is often referred to as the 'great imitator' due to its diverse clinical presentations across multiple stages. Neurosyphilis, a tertiary manifestation of Treponema pallidum infection, can present with neuropsychiatric features including rapid cognitive decline. It remains an important but potentially overlooked cause of cognitive impairment (CI). However, few cases document objective cognitive and functional improvement following treatment, especially within a short time frame. We describe the case of a 67-year-old man with rapid cognitive decline, displaying impairments in various cognitive domains: learning and memory, attention and executive functioning. The presence of Argyll-Robertson pupils combined with positive serological and cerebrospinal fluid testing confirmed a diagnosis of neurosyphilis. Following treatment with intravenous penicillin G, serial cognitive assessment demonstrated objective improvement in his cognition and functioning within 1 month of treatment. Our observation of such an improvement in neurosyphilis-driven CI in this time frame is a finding not commonly documented in associated literature. This case highlights the importance of thorough history taking, including a sexual history, alongside physical examination in diagnosing neurosyphilis. Additionally, it supports the importance of considering neurosyphilis when investigating patients with unexplained cognitive decline and suggests there is a degree of reversibility when treated promptly. Further research is needed to better characterise the treatability of neurosyphilis-related CI.