The diagnosis of neurosyphilis often poses a challenge, since there is no one test that is both sensitive and specific. The diagnosis is usually made based on a combination of reactive serologies, abnormalities of

CSF cell count and protein, or a reactive VDRL-CSF. The VDRL-CSF is the standard serologic test for CSF and is diagnostic of neurosyphilis when reactive (except in cases of gross contamination of CSF with blood). However, it is an insensitive test, so a negative result does not rule out the diagnosis. An FTA-ABS test on CSF appears to be more sensitive than the VDRL but may lead to more false-positive results and currently still has investigational status. The high sensitivity of the FTA-ABS CSF test may make it most useful in ruling out the diagnosis of neurosyphilis.

Typical abnormalities in the CSF profile in the setting of neurosyphilis include a mild mononuclear pleocytosis or an elevated protein level, or both, and these findings should be considered indicative of neurosyphilis in a patient with reactive serologic tests with or without clinical evidence of neurosyphilis.

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