Background: The origin of cerebrospinal fluid (CSF) syphilis antibodies (intrathecal or blood-derived) is in doubt. Little is known about CSF test behavior under the condition of physiological or disturbed functioning of blood-CSF barrier (BCB) and intrathecal immunoglobulin (Ig) production.
Methods: We collected 126 serum/CSF pairs from patients with serological evidence of syphilis. We explored the relationships between the established facts of intrathecal Ig synthesis and/or BCB dysfunction and the results of CSF diagnostic tests: the Treponema pallidum hemagglutination (TPHA) test, the fluorescent treponemal antibody absorption (FTA-Abs) test, the Venereal Disease Research Laboratory (VDRL) test, and white blood cell counts. We checked the criteria used either to support or refute the diagnosis of neurosyphilis.
Results: Reactive CSF-VDRL tests, elevated CSF–white blood cell counts, and elevated CSF-TPHA titers/indices were associated with the signs of intrathecal Ig synthesis, whereas nonreactive CSF–fluorescent treponemal antibody absorption, nonreactive CSF-TPHA tests, and CSF-TPHA titers from 1:4 to 1:160 were associated with cases where the intrathecal synthesis was not detected. There were some peculiarities of the tests toward BCB dysfunction.
Most of reactive CSF-VDRL test samples and CSF samples with pleocytosis were also meeting at least 1 of the CSF-TPHA titer/indices-based criteria. T. pallidum hemagglutination indices were in no better conformity with the facts of intrathecal immune response than CSF-TPHA titers.
Conclusions: Our findings have shown that all the examined criteria for the diagnosis of neurosyphilis in CSF are different assessment tools of intrathecal humoral immune activity and support the hypothesis that high CSF treponemal-specific antibody titers are a consequence of inflammatory pathology of the central nervous system.