The performance of rapid plasma reagin (RPR) titer in HIV-negative general paresis after neurosyphilis therapy

Background: Repeated nontreponemal serologic test for syphilis titers is recommended to evaluate treatment response. However, it is unknown whether serum rapid plasma reagin (RPR) titer can serve as a surrogate for determining the efficacy of treatment in general paresis (GP) remains unknown. Methods: We retrospectively reviewed data from 105 GP patients, who were divided into two groups (62 CSF RPR+ patients and 43 CSF RPR- patients) according to reactive RPR test status in CSF. Clinical assessment included the Mini-Mental State Examination (MMSE) scores, CSF examinations (WBC count, protein concentration and RPR titer), and serum tests (RPR titer and TPPA). Among the 105 GP patients, 13 CSF RPR+ patients and 6 CSF RPR- patients had a 12 months follow-up of CSF, serum measures and MMSE. Results: The median serum RPR titer was significantly higher in CSF RPR+ patients than that in CSF RPR- GP patients, 1:8 [IQR 1:4-1:32] vs. 1:4 [IQR 1:4-1:8] (P<0.001). The number of CSF RPR+ patients with serum RPR titer≥1:32 was significantly higher when compared with CSF RPR- patients (P=0.001). For CSF RPR+ patients, the MMSE scores improved or remained constantly after penicillin treatment. For CSF RPR+ patients, the CSF RPR titer declined four-fold in 85% (11/13) of the patients, whereas the serum RPR titer declined four-fold in only 46% (6/13) of the patients, the odds ratio is 6.4 (95% confidence interval 1.0-41.2). Conclusions: A four-fold decline in CSF RPR titer is a good predictor for treatment efficacy in CSF RPR+ GP patients within 12 months after the completion of therapy.