Development and External Validation of a Nomogram for Neurosyphilis Diagnosis Among Non-HIV Patients: A Cross-sectional Study

Background: The diagnosis of neurosyphilis (NS) is challenging due to the requirement of a lumbar puncture and cerebrospinal fluid (CSF) tests. Methods: This cross-sectional study constructed diagnostic models for diagnosing NS with data gathered from the Western China Hospital of Sichuan University between September 2015 and April 2021 and Shangjin hospital between September 2019 and April 2021, which formed the development and validation cohorts, respectively. A logistic analysis was performed to predict reactive neurosyphilis diagnosis and was presented as a nomogram. Clinical usefulness of the diagnostic models was assessed using a receiver operating characteristic (ROC) curve analysis, and Harrell C index was used for discrimination and calibration plots for accuracy, adopting bootstrap resampling 500 times. Results: : Overall, 149 and 67 patients were included in development and validation cohorts, respectively. Of those, 131 were diagnosed as havin g reactive NS with positive results in CSF treponemal and non-treponemal tests. In the development cohort, male sex, psychiatric symptoms, and serum toluidine red unheated serum test were selected as diagnostic indicators. The model reached 80% specificity, 79% sensitivity, and 0·85 area under the curves (AUC) (95% CI, 0·76-0·91). In the validation cohorts, the Harrell C index for the diagnostic possibility of reactive NS was 0·71. Conclusion: A convenient model using gender, presence of psychiatric symptoms and serum TRUST titre was developed and validated to indicate diagnostic results in patients suspected of NS. Checking model value of factors on nomogram is a feasible way to assist clinicians and primary health servers in updating patients’ medical chart and making quantitatively informed decision on NS diagnosis. Trial registration: This research was retrospectively registered in Ethics committee on biomedical research, West China Hospital of Sichuan University.