Metagenomic next-generation sequencing assists in identifying neurosyphilis: a case series

Neurosyphilis is a severe manifestation of syphilis caused by Treponema pallidum and remains challenging to diagnose because of heterogeneous clinical presentations and the limited performance of cerebrospinal fluid (CSF) assays. Here, we report four neurosyphilis cases in which CSF metagenomic next-generation sequencing (mNGS) detected T. pallidum and explore its potential value as an adjunctive diagnostic tool.

We retrospectively reviewed four HIV-negative adults treated at the Second Affiliated Hospital and Yuying Children's Hospital of Wenzhou Medical University in whom CSF mNGS detected T. pallidum and the overall clinical assessment supported neurosyphilis. Demographic data, presentations, neuroimaging, CSF parameters, serology, antimicrobial therapy, and outcomes were extracted from the medical records.

All patients had positive syphilis serology and inflammatory CSF profiles with lymphocytic pleocytosis (40-130 cells/µL) and elevated CSF protein (0.70-1.26 g/L). Brain magnetic resonance imaging (MRI) revealed non-specific chronic structural changes in all patients (including white matter hyperintensities, cerebral atrophy, and ventricular enlargement), with no acute ischemic, hemorrhagic, or neoplastic lesions. Bacterial cultures remained negative after 48 h. CSF mNGS detected T. pallidum in all cases (unique reads 8-135; standardized mapped reads number (SMRN) 1-53; genome coverage 0.0260-0.4945%), including three patients whose predominant presentations were neuropsychiatric. Following anti-treponemal therapy with ceftriaxone or penicillin, all patients showed clinical improvement.

In this case series, CSF mNGS provided direct detection of T. pallidum and supported the diagnosis of neurosyphilis in patients with diverse, often neuropsychiatric presentations when conventional microbiology was non-diagnostic. CSF mNGS may serve as a useful adjunct in selected patients, but results should be interpreted alongside clinical features and CSF inflammation rather than in isolation.