Point-of-care treponemal tests for neurosyphilis diagnosis.

BACKGROUND: The laboratory diagnosis of neurosyphilis rests upon identifying cerebrospinal fluid (CSF) abnormalities, including CSF-Venereal Disease Research Laboratory (VDRL) reactivity. The CSF-VDRL may not be available in the parts of the world where neurosyphilis is most common. Treponemal immunochromatographic strip tests (ICSTs) have been developed as point-of-care tests on blood for syphilis diagnosis in resource-limited settings. METHODS: We optimized 3 commercial ICSTs for performance on CSF and tested CSF samples from 217 patients with syphilis. The Syphicheck-WB test (Qualpro Diagnostics, Goa, India; "Syphicheck") was chosen for further study based on agreement with CSF-VDRL test results. We determined CSF-Syphicheck titers for 152 samples. We modified the CSF-Syphicheck for point-of-care testing in a US sexually transmitted diseases clinic and compared results on 102 paired centrifuged and uncentrifuged CSF samples obtained in the laboratory to the results obtained at point of care; results of samples diluted 1:4 were compared in a subset. RESULTS: The diagnostic sensitivity of a reactive CSF-Syphicheck (62%-64%) and the diagnostic specificity of a CSF-Syphicheck titer at or above 1:4 (79%-81%) were equivalent to the CSF-VDRL (54%-69% sensitivity, 73%-75% specificity) for laboratory and clinical neurosyphilis diagnoses. The CSF-Syphicheck normalized after neurosyphilis therapy similarly to the CSF-VDRL. The modified CSF-Syphicheck performed well at the point of care, albeit with better performance on cell-free compared with uncentrifuged CSF. CONCLUSIONS: Cerebrospinal fluid treponemal ICSTs hold promise for point-of-care neurosyphilis diagnosis in regions where the CSF-VDRL is not available. Further study should address the performance of CSF ICSTs in resource-limited settings.

Toll-like receptor polymorphisms are associated with increased neurosyphilis risk.

BACKGROUND: Single-nucleotide polymorphisms (SNPs) in toll-like receptors (TLR) 1, 2, and 6 impair cell signaling in response to spirochetal lipoproteins. We investigated whether common SNPs in TLR1, TLR2, or TLR6 were associated with laboratory- or clinically-defined neurosyphilis. METHODS: Polymorphisms in the genes for TLR1 (a T→G mutation at position 1805), TLR2 (a G→A mutation at position 2258), and TLR6 (a C→T mutation at position 745) were sought in 456 white patients with syphilis. Laboratory-defined neurosyphilis included a reactive cerebrospinal fluid (CSF)-Venereal Disease Research Laboratory (VDRL) test. Clinically-defined neurosyphilis included new vision or hearing loss. Controls had CSF white blood cells of 5/µL or less, nonreactive CSF-Venereal Disease Research Laboratory, and no vision or hearing loss. RESULTS: Overall, 26.2% of patients had laboratory-defined and 36.2% had clinically-defined neurosyphilis. Compared with controls, patients with any of the 3 SNPs were more likely to have laboratory-defined neurosyphilis. Those with TLR2 or TLR6 SNPs were more likely to have clinically-defined neurosyphilis. These associations were independent of serum rapid plasma reagin titer. CONCLUSIONS: A common TLR1 polymorphism is associated with an increased risk of laboratory-defined neurosyphilis, and common TLR2 and TLR6 polymorphisms are associated with an increased risk of both laboratory- and clinically-defined neurosyphilis. These data suggest that host factors impact the natural history of syphilis.

The rapid plasma reagin test cannot replace the venereal disease research laboratory test for neurosyphilis diagnosis.

BACKGROUND: The cerebrospinal fluid (CSF) Venereal Disease Research Laboratory (VDRL) test is a mainstay for neurosyphilis diagnosis, but it lacks diagnostic sensitivity and is logistically complicated. The rapid plasma reagin (RPR) test is easier to perform, but its appropriateness for use on CSF is controversial. METHODS: RPR reactivity was determined for CSF from 149 individuals with syphilis using 2 methods. The CSF-RPR was performed according to the method for serum. The CSF-RPR-V was performed using the method recommended for the CSF-VDRL. Laboratory-defined neurosyphilis included reactive CSF-fluorescent treponemal antibody absorption test and CSF white blood cells >20/uL. Symptomatic neurosyphilis was defined as vision loss or hearing loss. RESULTS: CSF-VDRL was reactive in 45 (30.2%) patients. Of these, 29 (64.4%) were CSF-RPR reactive and 37 (82.2%) were CSF-RPR-V reactive. There were no instances where the CSF-VDRL was nonreactive but the CSF-RPR or CSF-RPR-V was reactive. Among the 28 samples that were reactive in all 3 tests, CSF-VDRL titers (median [IQR], 1:4 [1:4-1:16]) were significantly higher than CSF-RPR (1:2 [1:1-1:4], P = 0.0002) and CSF-RPR-V titers (1:4 [1:2-1:8], P = 0.01). The CSF RPR and the CSF-RPR-V tests had lower sensitivities than the CSF-VDRL: 56.4% and 59.0% versus 71.8% for laboratory-diagnosed neurosyphilis and 51.5% and 57.6% versus 66.7% for symptomatic neurosyphilis. CONCLUSIONS: Compared with the CSF-VDRL, the CSF-RPR has a high false-negative rate, thus not improving upon this known limitation of the CSF-VDRL for neurosyphilis diagnosis. Adapting the RPR procedure to mimic the CSF-VDRL decreased, but did not eliminate, the number of false negatives and did not avoid all the logistical complications of the CSF-VDRL.