Neurosyphilis is a difficult clinical stage of syphilis as there is no ideal method for diagnosis and workup requires lumbar puncture which may sometimes provide ambiguous results especially in HIV co-infected patients. Enzyme immunoassay is a widely used screening test for syphilis in serum, its test performance was not well studied in cerebrospinal fluid.

To examine the diagnostic performance of cerebrospinal fluid-enzyme immunoassay in neurosyphilis.

This is a prospective study with a time span of two years. All consecutive patients admitted for workup of neurosyphilis under the Social Hygiene Service, the major public service provider of sexually transmitted disease in Hong Kong, were included. Laboratory tests on cerebrospinal fluid included venereal disease research laboratory, fluorescent treponemal antibody-absorption, Treponema pallidum particle agglutination, enzyme immunoassay syphilis, cerebrospinal fluid cell count, and protein. Performances of the above tests were evaluated and compared using The International Union Against Sexually Transmitted Infections 2008 guidelines.

Forty-five patients were prospectively recruited, of which 29 people were living with HIV / AIDS. Using diagnostic case definition standard stipulated in The International Union Against Sexually Transmitted Infections 2008 guidelines, 17 patients satisfied the diagnosis of neurosyphilis. Cerebrospinal fluid-enzyme immunoassay test provided 100% in both sensitivity and negative predictive value, specificity was 46.4% (13/28, 95% CI 31.8–61%). Specificity improved to 80.8% (95% CI: 68.4–93.2%) with optical density cut-off value at 1.4 for cases with cerebrospinal fluid-red cell counts <600/mm³.

This is the first study on use of cerebrospinal fluid-enzyme immunoassay in neurosyphilis. Cerebrospinal fluid-enzyme immunoassay showed high sensitivity and high negative predictive value in the study population. cerebrospinal fluid-RBC less than 600/mm³ may not affect its accuracy.