Significance of laboratory findings for the diagnosis of neurosyphilis

Our objective is to assess the specificity and sensitivity, and thus elaborate the relevance, of different laboratory findings for the diagnosis of neurosyphilis. One hundred and fourteen HIV-negative pairs of serum and cerebrospinal fluid (CSF) samples were examined by the Venereal Disease Research Laboratory (VDRL) test, a fluorescent treponemal antibody-absorption (FTA-ABS) test, microhaemagglutination assay with Treponema pallidum antigen (MHA-TP) test (serum) and Treponema pallidum haemagglutination assay (TPHA) test (CSF); further, albumin, total protein, and total IgG were determined and, in the CSF, cell count was performed. The donors were 60 patients with active neurosyphilis and 54 healthy persons with a former history of syphilis and with persisting positive results in the T. pallidum haemagglutination tests (serum: MHA-TP, CSF: TPHA), who supplied specimens for control. Albumin quotient, IgG index, TPHA index, modified TPHA index, Intrathecally produced T. pallidum Antigen (ITpA) index, its 2 modifications and, in 12 samples, the adenovirus group antibody (AVGA)/TPHA index were ascertained. The specificity and sensitivity of the TPHA index were 100% and 98.3%, of the modified TPHA index 50.0% and 96.7%, of the ITpA index 42.6% and 90.0%, of the modified ITpA indices 51.8% and 68.3% (first modification) and 53.7% and 63.3% (second modification). The AVGA/TPHA index yielded a specificity of 91.7% (11/12). The CSF VDRL test was positive in 55/60 (91.7%) of samples from patients with neurosyphilis and in none of the controls (0/54). A CSF-TPHA titre greater than 1:320 was observed in 59/60 (98.3%) of the neurosyphilis specimens and in none of the controls (0/54). A TPHA index above an outcome of 70, a positive CSF-TPHA test at a titre greater than 1:320 and, with lower sensitivity, the criteria of the Centers for Disease Control (CDC) guidelines yield the most reliable results for laboratory support to a diagnosis of neurosyphilis. The modified TPHA index, the ITpA index, and its 2 modifications produce results of minor sensitivity and poor specificity. Observations on the AVGA/THPA index are too limited yet for judgement. The diagnostic significance of a CSF-TPHA titre above 320 needs further confirmation on a greater number of observations made by different laboratories.