Diagnosis of neurosyphilis by examination of the cerebrospinal fluid.

Thirty-six patients with reactive results in the cerebrospinal fluid to the Treponema pallidum haemagglutination assay (CSF-TPHA) were investigated by further serological tests for confirmation of active neurosyphilis. The results of the TPHA and fluorescent treponemal antibody tests were reactive in all CSF samples from patients with acute untreated neurosyphilis and from most patients with late latent syphilis but no signs of involvement of the central nervous system. The demonstration of 19S-IgM antibodies against Treponema pallidum in the CSF was a better indication of activity of the disease than the Venereal Disease Research Laboratory test. Ten of 11 patients with untreated acute neurosyphilis had reactive results in the solid-phase haemadsorption test for CSF-IgM (CSF-IgM-SPHA test). The TPHA index, which relates the CSF-TPHA titre to the albumin quotient and thus excludes errors from disturbed function of the blood-brain barrier, was above 100 in all but one of the patients with acute neurosyphilis but below 100 after treatment. Patients with late latent syphilis and without CNS signs had TPHA indices below 5. Thus a nonreactive CSF-TPHA test result excludes neurosyphilis but reactive CSF-IgM-SPHA results and TPHA indices above 100 strongly indicative active disease.