Which cerebrospinal fluid (CSF) findings indicate neurosyphilis?

Updated: Jul 17, 2018
  • Author: Richard P Knudsen, MD, FAAN, FAAP; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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The diagnosis of neurosyphilis is based on a CSF WBC count of 20 cells/µL or greater, and/or a reactive CSF VDRL, and/or a positive CSF intrathecal T pallidum antibody index. [46]

CSF abnormalities include elevated protein levels and pleocytosis, which are found in up to 70% of patients. In addition, the CSF VDRL result is reactive. CSF examination is recommended in all patients with untreated syphilis of unknown duration or of duration greater than 1 year. Because standard PCN-G benzathine therapy for early syphilis does not achieve treponemicidal levels in the CSF, some experts advise lumbar puncture in persons with secondary and early latent syphilis, with follow-up examinations for patients with abnormalities.

Perform lumbar puncture in the evaluation of latent syphilis of more than 1-year duration, in suspected neurosyphilis, and in late complications other than symptomatic neurosyphilis because asymptomatic neurosyphilis may coexist with other late complications. A serum RPR titer of 1:32 seems to be the best cutoff point to decide whether or not to perform a lumbar puncture. [46] Abnormal CSF findings can then be serially monitored as a guide to therapy. Overall, CSF pleocytosis continues to define disease activity. Documentation of resolution of CSF findings following therapy is required to confirm curative treatment.

Caution must be exercised before performing a lumbar puncture if the patient has neuroimaging evidence of a gumma (ie, space-occupying lesion) because cephalocaudad herniation is a possibility.

Demonstration of the spirochetes in lesions of primary and secondary syphilis using dark-field examination currently is the criterion standard for the laboratory diagnosis of syphilis. However, the diagnosis of neurosyphilis is based on clinical grounds (ie, neurological manifestations, CSF findings, and serologic evidence of exposure to the organism).

Perinatologists are exploring the clinical merit or value of CSF beta2-microglobulin, levels of which are elevated in cases of congenital syphilis. This beta2-microglobulin could serve as a valid new biologic marker useful in the diagnosis of CNS involvement and could be useful in monitoring the response to therapy. [47]

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