Comparison of molecular and serological assays on cerebrospinal fluid for the diagnosis of neurosyphilis.

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Many assays are available on cerebrospinal fluid (CSF) for the diagnosis of neurosyphilis (NS) but there is no 'gold standard'. The aim of this study was to evaluate different molecular and serological assays used in NS. We evaluated two PCR assays and three serological techniques in parallel on CSF samples collected between 2019 and 2020 from patients suspected of NS. The study included 143 patients comprising 30 early NS, 7 late NS and 106 patients without a diagnosis of NS. All patients with NS were symptomatic and had either neurological (67.6%) or ophthalmological signs (54.1%). The qPCR and nPCR assays had overall sensitivities (Se) of 41% and 27%, respectively; with each an overall specificity (Sp) of 100%. VDRL had a Se of 51% and a Sp of 92%. Immunoblot had a Se of 62% and a Sp of 85%. Finally, treponemal tests (TT) had a Se of 96% and a Sp of 69%. Our study confirms the excellent specificity of molecular techniques allowing to avoid overdiagnosis of NS, and thus, unjustified intensive antibiotic therapy protocols. CSF TT, although not very specific, has an excellent Se confirming that there is almost never NS with negative CSF TT. VDRL and immunoblot tests have better overall diagnostic performance. However, none of these techniques has sufficient diagnostic performance to represent a 'gold standard'. Thus, the diagnosis of NS relies on a combination of clinical and biological parameters with the association of PCR with serology, associating VDRL and immunoblot, in CSF.