Elevation of Cerebrospinal Fluid Light and Heavy Neurofilament Levels in Symptomatic Neurosyphilis

BACKGROUND: Although clinical manifestations of symptomatic and asymptomatic neurosyphilis are different, few laboratory tests could reflect the difference. METHODS: A total of 92 non–HIV-infected patients with syphilis were enrolled in this study, including 23 with symptomatic neurosyphilis, 51 with asymptomatic neurosyphilis, and 18 with latent syphilis, which were excluded neurosyphilis because they were found to have no symptom and normal cerebrospinal fluid (CSF) tests and served as the control group. The concentrations of neurofilament light subunit (NF-L) and phosphorylated neurofilament heavy subunit (pNF-H) in the CSF were measured and compared among these groups, as well as before and after treatment in the symptomatic and asymptomatic groups. RESULTS: The median concentrations of NF-L in the symptomatic neurosyphilis, asymptomatic neurosyphilis, and control groups were 5806, 218, and 266 pg/mL, respectively (P < 0.001), and the median concentrations of pNF-H were 986, 43, and 49 pg/mL, respectively (P < 0.001). A subgroup of 15 symptomatic neurosyphilis and 10 asymptomatic neurosyphilis patients were followed up and underwent CSF examination 6 months after the antineurosyphilis treatment. The median concentration of NF-L in the symptomatic neurosyphilis group decreased from baseline 6420 to 2914 pg/mL after the treatment (P = 0.03), and the median concentration of pNF-H in the symptomatic neurosyphilis group decreased from baseline 1399 to 246 pg/mL after the treatment (P = 0.03). CONCLUSIONS: Neurofilament light subunit and pNF-H were significantly elevated in the symptomatic neurosyphilis patients, not in asymptomatic neurosyphilis, which was an implication of the different pathogeneses in neurosyphilis.