Clinical and laboratory data-based nomograms for neurosyphilis diagnosis in non-HIV syphilis patients: a cross-sectional study.

Abstract

was constructed to readily provide the probability of diagnosis at point of care and presented as two nomograms.The basic model reached 79% specificity, 74% sensitivity and 0.82 Area Under the Curves (AUC) (95% CI, 0.72-091), while the combined model showed 82% specificity, 90% sensitivity and 0.88 AUC (95% CI, 0.80-0.94).The integrated discrimination improvement (IDI) index was 0.05 in comparison of two models.

Conclusions:
A convenient model using serum TRUST titre and presence of psychiatric symptoms was developed to indicate diagnostic results in patients suspected of NS.
Two simple nomograms can be offered to clinicians to facilitate their assessment of patient diagnosis, strengthen the diagnostic decision making, enhance patient stratification, and inform patients in the clinic.

Trial registration:
This research was retrospectively registered in Ethics committee on biomedical research, West China Hospital of Sichuan University.

Background
Neurosyphilis (NS) is one of the most feared complications of syphilis [1], and the dissemination of the pathogenic bacterium of NS, Treponema pallidum (TP), to the cerebrospinal fluid (CSF) and meninges can occur at any stage of the infection [1].
Importantly, the injury of brain tissues caused by TP invasion is irreversible [1].
Trend results from syphilis notification data of the 25 countries with comprehensive surveillance systems showed an increase, especially in Europe, of up to 70% since 2000 [2,3].However, the proportion of NS among syphilis patients is undetermined due to diagnostic limitations, requiring skilful doctors to perform lumbar puncture and lab operators for special tests [4].Resources are usually not available to primary community healthcare centres of urban districts or common hospitals in smaller areas [5].
Prior to the advent of antibiotics, the typical symptoms of NS, such as pupil constriction when the eyes focus on a nearby object but not when the pupil is illuminated (Argyll Robertson pupils), were used to diagnose NS [1].However, access to antibiotics has greatly increased, affecting the disease process and manifestation of NS [6].Whether signs and symptoms can facilitate NS identification remains controversial.In recent years, headache and blurred vision are reported as supportive factors of NS diagnosis [7,8], while other reports suggest various clinical manifestations of NS lack of specificity [9].Furthermore, most of the descriptions of NS symptoms come from reports on American cohorts co-infected with HIV [8,10], which lack information on non-HIV NS patients, which constitute the majority of NS patients in Europe and Asia [9,11].
The laboratory diagnosis of NS was putatively based on positive results from serum and CSF serologic tests, as well as elevations in CSF white-cell count and protein levels [12,13].In 2015, an American guideline from Centers for Disease Control and Prevention (CDC), U.S. department of health and human services suggested the use of a decision tree for NS diagnosis, sequentially requiring a positive or reactive definition of non-specific, specific, or alternative tests in CSF for suspected NS patients [12].A European guideline on European Academy of Dermatology and Venerology recommends the cut-off value of CSF treponemal tests in patients coinfected with HIV [13].In fact, even the best threshold and combined usage of diagnostic tests for NS needs extra validation in post-antibiotics era [14].
Furthermore, combining continuous variables with clinical parameters and presenting them in a visual graph, a nomogram, which transforms a multivariable regression equation into a single numerical estimate of the probability of an event and widely used in the field of cancer diagnosis or prognosis, makes the results of a diagnostic model more simple-to-use and facilitates the evaluation of NS patients, especially in poor areas that lack expert operators and the ability to perform time-consuming tests [15].Unfortunately, Chinese guidelines do not elaborate on the relationship between treponemal test titre and NS diagnosis, although they do recommend using CSF nucleated cells (>5 cells/ul, positive) or CSF protein concentration (>0.45 g/l, positive) as binary variables [16].Recent studies estimating serologic cut-off values have found that the accuracy of NS diagnosis depends on the choice of controls with various clinical characteristics.In fact, both serum tests and CSF assessments have been validated as objective indicators supporting diagnosis [8,17].The present study was designed to verify and explore the association between these factors and diagnostic confirmation using data from patients at the West China Hospital, Medical College of Sichuan University, from September 2015 to September 2019.Using clinical and laboratory characteristics, we developed two feasible diagnostic nomograms in order to assess the possibility of NS in an HIV-negative population with an unknown syphilis duration.

Diagnostic criteria
Subjects were enrolled at West Hospital of Sichuan University (n＝230).One hundred and eight patients fulfilled all of the following criteria: (1) positive in serum TPPA and TP-CLIA; (2) positive in both CSF-TRUST and CSF-TPPA; (3) exclusion of HIV diagnosis (Figure 1).We applied a strict diagnostic criterion in combination of two laboratory methods to ensure the specificity and diagnose neurosyphilis in the suspected participants.Thus, patients with double positive results of both CSF-TRUST and CSF-TPPA were assigned into the confirmed reactive NS group, and the others to the control group.

Laboratory methods
Baseline serum samples were collected within four days of the lumbar puncture [8].

Statistics
Associations between categorical variables were assessed using a chi-squared test or All analyses were weighted according to the analytical guidelines.P-values < 0.05 were considered statistically significant.R software (version 3.3.1;http://www.Rproject.org)were used for analysis.

Results
Table

Laboratory findings and diagnostic yield
The univariable logistic regression revealed significant differences in CSF protein levels between the reactive neurosyphilis group and the control group (odds ratio [OR], 96.54; 95% confidence interval [CI], 9.52-978.55,P < 0.0001;  2).
However, no difference in creatine kinase levels was observed between the confirmed reactive neurosyphilis and control groups (OR, 1.0; 95% CI, 1.00-1.01).Moreover, there were no significant differences between these two groups in serum IgG and albumin levels, which contribute to the calculation of a potential effective CSF synthesis index (OR, 1.55; 95% CI 1.10-2.20)NS in patients with a serum TRUST titre ≥1:64 [17].Researchers noted that an increase in serum TPPA titre and serum creatine kinase could serve as a surrogate for CSF clinical abnormalities after lumbar punctures [17,18].Unfortunately, we were unable to determine titre grades of serum TPPA, since the laboratory system of our hospital automatically sets and reports serum TPPA >1:320 as positive.Nonetheless, once infected, serum TPPA remains positive during a patient's lifetime, so we did not include this item in order to minimize the false positive rate.

Conclusions
The present study showed that psychiatric symptoms, serum TRUST, and CSF This study included consecutive patients presenting with positive results of serum non-treponemal (Treponema Pallidum chemiluminescence assay [TP-CLIA] or Treponema Pallidum particle agglutination assay [TPPA]), and a treponemal serological test (toluidine red unheated serum test [TRUST] ) from the West China Hospital, Medical College of Sichuan University from September 2015 to September 2019.Patients met one of the following criteria: neurological or ophthalmological symptoms or signs during any stage of syphilis (such as headache, photophobia, blurred version, confusion, sleep disorders, vertigo, hearing loss, version loss, confusion, lethargy, memory change, progressive dementia, psychiatric symptoms, personality change, numbness, fatigue or pain in limbs and trunk, seizure, tremor) and no symptom) or syphilis of unknown duration, or failure of antibiotic treatment in syphilis patients (titre of serum non-treponemal test fail to decrease and fix after antibiotic treatment).There were two types of diagnostic models: Model 1 (basic model), clinical parameters other than CSF test findings and Model 2 (combined model), combined model of both clinical parameters and CSF test findings.

Fisher's exact
test.Associations between continuous variables and categorical variables were assessed using a Mann-Whitney U test.Diagnostic factors were analysed using univariable and multivariable regression models for confirmation of reactive NS or not -including non-reactive and not NS-as binary classification out of clinical consideration.A two-tailed P value >0.05 was used for removal of variables.Indicators having great clinical relevance were forced back into the model.CSF items from clinical guidelines were assessed for possible additional effects.Boot strapping was resampled 500 times to obtain a 95% confidence interval and quantify the effects of diagnostic indicator selection strategies on the model development.Performance measures included the average area under the ROC curve, sensitivity, and specificity.

Figure 2 .
Figure 2. ROC curve, DCA and nomograms protein correlated with a diagnosis of NS in non-HIV NS.Further, a convenient score model was developed to indicate diagnostic results in suspected NS patients with or without a lumbar puncture.Importantly, two nomograms can be offered to clinicians to improve their abilities to assess patient diagnosis, strengthen diagnostic decision making and inform patients in the clinic.To increase its applicability, future studies should focus on internal improvement and external validation.Treponema pallidum TPCA: Treponema pallidum chemiluminescence assay TPPA: Treponema pallidum particle agglutination assay TRUST: toluidine red unheated serum test VDRL: Venereal Disease Research Laboratory Declarations: Ethics approval and consent to participate All methods were carried out in accordance with Transparent Reporting of a multivariable prediction model for Individual Prognosis or Diagnosis (TRIPOD) guidelines and regulations.

Figures
Figures

1 Baseline characteristics of the participants
year period are summarised in Table1.The median age of all study participants was 46 years old (range 17-84 years).Men accounted for 82.9% of the 76 reactive NS patients (mean age, 47 years).The most common symptom of NS was cognitive dysfunction (31.0%), which was mainly presented as memory change.Other symptoms included sleep disorders, photophobia, blurred version and et al.In addition, among 108 patients11(10.2%) were non-symptomatic patients and required a CSF test.Seventy-six patients (73.8%) did not receive any prior antibiotic treatment.Twenty-seven patients were unsuccessfully treated with nonspecific therapy for neuropsychiatric symptoms before the correct diagnosis was reached.

Table 2 . Association between each indicator and diagnostic outcome
unheated serum test; Cerebrospinal fluid, CSF; Immunoglobulin, IgG.*Data with normal distribution was described using mean (sd).

Table 4 . ROC Curves, AUC and nomograms of models for NS diagnosis using multivariable logistic regression modelling
This study had several limitations.First, the study might suffer from sampling bias.We did not exclude patients who received insufficient antibiotic therapy before lumbar puncture.The number of Treponema pallidum correlated with disease activity in patients, but we did not exclude such cases.Among those, the diagnosis was set as a binary variable.Under this criterion of group assignment, false negatives were possible due to non-reactive NS cases.In theory, disease duration should have been analysed as a risk factor for NS, but it is difficult for patients with neuropsychological symptoms to provide the exact time of syphilis infection or information on sexual activities.Additionally, another limitation was the small sample size and that the sophisticated pathological categories of NS were not employed here.Whether patients in each dedicated category had a different prognosis or not remains unknown due to lack of follow-up investigation.We are building up a systematic database and prospectively designing new studies to improve the quality of the evidence and facilitate more comprehensive patient care.Lastly, in order to verify the validity of this model, future studies are warranted.