Different cerebrospinal fluid levels of Alzheimer-type biomarker Aβ42 between general paresis and asymptomatic neurosyphilis

Background and purpose Neurosyphilis is a neurological disease that involves infection of the central nervous system with Treponema pallidum. With increases in unsafe sexual behaviour, syphilis has re-emerged worldwide. To explore the amyloid and tau metabolism in neurosyphilis patients in different stages, the levels of Alzheimer-type biomarkers in general paresis (GP) and asymptomatic neurosyphilis (ANS) patients in comparison to patients with Alzheimer's disease (AD) and normal controls (NCs) were investigated. Methods β-amyloid peptide 1-42 (Aβ42) and Aβ 1-40 (Aβ40), tau hyperphosphorylated at threonine 181 (p-tau181) and total tau (t-tau) in cerebrospinal fluid (CSF) were measured by enzyme-linked immunosorbent assay kits in 44 patients with GP, 10 patients with ANS, 45 patients with AD and 39 NCs. Results Alzheimer's disease patients had lower CSF Aβ42 levels combined with higher CSF t-tau and p-tau181 levels than other groups (all P < 0.001). The CSF Aβ42 levels decreased in GP compared to ANS and NCs (P < 0.001). CSF Aβ40, t-tau and p-tau181 levels were not different between the GP, ANS or NC groups. Conclusions Our research has demonstrated that GP, ANS and AD patients are characterized by distinct patterns of the CSF biomarkers Aβ and tau. The distinct CSF Aβ pattern in GP suggests the existence of abnormal Aβ metabolism. Furthermore, different levels of CSF Aβ will be helpful for the differentiation between different stages of neurosyphilis.