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STD Institute, Shanghai Skin Disease Hospital, School of Medicine, Tongji University, Shanghai 200443, ChinaShanghai Skin Disease Clinical College of Anhui Medical University, Shanghai Skin Disease Hospital, Shanghai 200050, People's Republic of China
To uncover the role of the platelet indices in patients with syphilis.
Methods
A total of 2061 patients with syphilis and 528 healthy controls were enrolled in this retrospective cohort study. The data of platelet count (PLT), mean platelet volume (MPV), platelet distribution width (PDW), and indicators of syphilis activities were collected. The correlations between the platelet indices and disease activities were analyzed.
Results
A total of 425 (20.6%) of the 2061 patients were of primary and secondary syphilis, 433 (21.0%) latent, 463 (22.5%) serofast, 350 (17.0%) asymptomatic neurosyphilis, and 390 (18.9%) symptomatic neurosyphilis. Compared with the healthy controls, PLT was significantly increased in the primary and secondary syphilis group; whereas, MPV and PDW were significantly decreased in all stages of syphilis. These changes of platelet indices were reversed after anti-treponemal therapy. Further correlation analysis showed that PLT was positively associated with the syphilis activity indicators [rapid plasma reagin (RPR) titer, cerebrospinal fluid white blood cell (CSF-WBC), CSF-protein, and CSF-VDRL (venereal disease research laboratory)] and inflammatory markers [WBC, C-reaction protein (CRP), and erythrocyte sedimentation rate (ESR)]. Conversely, PDW was negatively correlated with all of these parameters. MPV had an inverse relationship with RPR, ESR, and CRP.
Conclusions
Platelet indices are associated with syphilis activities.
Caused by Treponema pallidum (T. pallidum), syphilis is a chronic sexually transmitted disease that has highly variable clinical courses and manifestations from a painless chancre to severe damage in the brain, heart, and other organs (
), and China has become the first casualty. In 2019, 587,464 new syphilis cases were reported in China, and the incidence of syphilis was 38.37 per 100,000 (
) underscores the importance of the disease activity indices in syphilis research. As reported, during the syphilitic infection, a number of indices were believed to be associated with the disease activities. The serum nontreponemal specific tests such as rapid plasma reagin (RPR) titer serve as an index of syphilis activities and also for evaluating the treatment response. The venereal disease research laboratory (VDRL) titer, white blood cell (WBC) counts, and protein concentration in cerebrospinal fluid (CSF) are used as diagnostic indicators of neurosyphilis as well as the surrogates for evaluating the treatment response (
). In addition, it also has been reported that inflammatory markers, WBC, erythrocyte sedimentation rate (ESR), and C-reaction protein (CRP) were increased in patients with syphilis, especially in early syphilis (
). Platelet count (PLT), mean platelet volume (MPV), and platelet distribution width (PDW) are the most commonly used indicators to evaluate platelet activation and function. Increased PLT was found in community-acquired pneumonia, septic arthritis, active pulmonary tuberculosis (PTB), Clostridium difficile infection (CDI), and bronchiolitis (
The evaluation of platelet indices and markers of inflammation, coagulation and disease progression in treatment-naïve, asymptomatic HIV-infected individuals.
). In patients with chronic hepatitis C virus (HCV) infection, platelet indices were abnormal (decreased PLT and increased MPV/PDW) and were believed to be useful in evaluating liver fibrosis progression (
). Together, all these previous studies indicated that the platelets might be involved in the pathogenesis of syphilis. However, the whole pattern of platelet indices in syphilis is unknown.
Methods
Data collection of the participants
This retrospective cohort study was conducted at the Shanghai Skin Disease Hospital from January 2015 to May 2021. The study was approved by the Ethics Committee of the Shanghai Skin Disease Hospital. A total of 2061 patients with syphilis (425 primary and secondary syphilis, 433 latent syphilis, 463 serofast syphilis, 350 asymptomatic neurosyphilis, and 390 symptomatic neurosyphilis, respectively) were enrolled. Among them, 209 patients with neurosyphilis were followed until the end of the treatment. In addition, 528 healthy controls were enrolled during the study, with matched age and sex. Data of ESR, CRP, serum RPR, CSF-VDRL, CSF-WBC count, and CSF-protein concentration were collected from patients’ medical records.
Inclusion and exclusion criteria
The diagnostic criteria of primary, secondary, latent, and serofast syphilis were as we previously described (
). The diagnosis of neurosyphilis was based on a reactive CSF Treponema pallidum particle agglutination (TPPA) and a reactive CSF-VDRL without substantial blood contamination in CSF or negative CSF-VDRL but positive CSF-TPPA with CSF protein concentration >0.45g/L and/or CSF-WBC count ≥8/μL (
). Asymptomatic neurosyphilis was defined by the absence of neurological/psychiatric symptoms or signs but with the presence of CSF abnormalities. Symptomatic neurosyphilis was characterized by the presence of neurological/psychiatric symptoms or signs and CSF abnormalities (
). The exclusion criteria for both patients and controls included pregnancy, malignant tumors, HIV infection, history of systemic inflammatory diseases, cardiovascular and cerebrovascular diseases, metabolic diseases, chronic infection diseases, use of antibiotics medications in the last four weeks, and smokers and drinkers.
Statistical analysis
GraphPad Prism version 8.0.2 (GraphPad Software) was used for the statistical analysis. The numeric variables were presented as the median and interquartile range (IQR) and categorical variables were presented as frequency and percentage. Categorical variables were compared by the chi-square test. All the datasets were evaluated for deviation from a normal distribution using D'Agostino-Pearson omnibus normality test. Differences between groups were analyzed by using Student t test and one-way ANOVA if the condition of normal distribution was met, otherwise Mann-Whitney U test and Kruskal-Wallis test were used. Spearman correlation analyses were performed to investigate the correlations between platelet indices with related parameters such as WBC, ESR, CRP, and RPR in blood and WBC, protein, and VDRL in CSF. Probability (p) values <0.05 were considered statistically significant.
Previous reports indicated that platelet indices were influenced by factors of sex and age (
). To avoid the biases affected by the factors above, we then further divided sex and age accordingly. The healthy controls and syphilis groups were further divided into four age groups based on the age range.
Results
Clinical and laboratory characteristics of the participants
From January 2015 to May 2021, a total of 6018 hospitalized patients with syphilis in Shanghai Skin Disease Hospital were screened for this study. Of those, 3957 were excluded because of the presence of other diseases (cardiovascular and cerebrovascular diseases n=1682; metabolic diseases n=291; chronic infectious diseases n=245; HIV infection n=348; malignant tumors n=61; autoimmune diseases n=21; systemic inflammatory diseases n=56; history of antibiotics in last four weeks n=73; pregnancy n=81; and smokers and/or drinkers n=1099) (Figure 1). A total of 2061 patients were then enrolled in this study, including 425 (20.6%) primary and secondary syphilis, 433 (21.0%) latent syphilis, 463 (22.5%) serofast syphilis, 350 (17.0%) asymptomatic neurosyphilis, and 390 (18.9%) symptomatic neurosyphilis. In addition, 528 healthy controls were enrolled. The clinical and laboratory characteristics of the participants were described in Table 1. Among them, the primary and secondary syphilis group has the highest serum RPR titer (median=1:64). The CSF-WBC count and CSF-protein in patients with neurosyphilis were significantly higher than those in the non-neurosyphilis group (p<0.001). There was no difference in sex between healthy controls and each syphilis group. Although significant differences in age from the overall analysis were observed among four age groups, there were no differences between healthy controls and each syphilis group (Table 1).
Figure 1Enrollment flow diagram of patients with syphilis.
PLT was significantly increased in patients with primary and secondary syphilis, whereas MPV and PDW were dramatically decreased in patients with nearly all stages of syphilis.
Table 1 presents that the median value of PLT was significantly higher in primary and secondary syphilis than in healthy controls (260 with IQR 216-313 vs 225 with IQR 197-254, p<0.001), and the PLT median value of other groups compared with healthy controls was not significant. Comparative analysis was then conducted independently in each age group. As shown in Figure 2A, compared with that from the healthy controls, the PLT was significantly elevated in patients with primary and secondary syphilis in all age groups (p<0.01). The median of PLT was the highest in the group of age ≤30 in primary and secondary syphilis. However, in other patient groups (serofast, latent, asymptomatic neurosyphilis, and symptomatic neurosyphilis), the elevation of PLT was not observed, except in age 31-44 group of patients with latent syphilis. In patients with latent syphilis, PLT only increased in age 31-44 group compared with the healthy controls (p=0.032) (Figure 2A).
Figure 2Comparison of PLT(A), MPV(B), and PDW(C) in patients with different stages of syphilis and healthy controls at different age groups. Differences between groups were analyzed by the Kruskal-Wallis test. The value of p<0.05 was considered significant. ns, no significant.
In addition to PLT, the alternations of MPV and PDW were also observed in patients with syphilis. The MPV median values of 5 syphilis groups (primary and secondary, serofast, latent, asymptomatic neurosyphilis, and symptomatic neurosyphilis) and controls were 8.5 with IQR 7.9-9.3, 8.9 with IQR 8.1-9.7, 9.1 with IQR 8.4-9.9, 8.7 with IQR 8.1-9.5, 8.6 with IQR 7.9-10, and 10.3 with IQR 9.7-11.1; and the MPV was lower than that from controls in each syphilis group, respectively (p<0.001). The median values of PDW were also detected in experimental and control groups (15.5 with IQR 12.5-15.9, 15.7 with IQR 13.8-16.1, 15.9 with IQR 14.6-16.2, 15.7 with IQR 13.8-16.1, 15.5 with IQR 13.0-16.0, and 16.1 with IQR 15.6-16.4); and PDW medians were also decreased in syphilis groups (p<0.001) (Table 1). Comparative analysis was further conducted in each age group. As shown in Figure 2B, MPV was significantly lower in patients with syphilis with all stages than that in healthy controls in each age group (p<0.01), except for symptomatic neurosyphilis in the age ≤30 group. The value of PDW was also significantly decreased in patients with syphilis with all stages, except in patients with serofast syphilis in the age 31-44 group (p<0.05) (Figure 2C).
To further confirm if the changes of platelet indices were because of T. pallidum infection in patients with syphilis, the paired data of before and after treatment in a total of 209 patients with neurosyphilis were analyzed. As shown in Figure 3, PLT was significantly reduced after therapy (218 vs 202, z=-12.5, p=0.001), whereas MPV and PDW were significantly elevated after therapy (8.4 vs 8.7, z=-3.56, p<0.001; 15.5 vs 15.9 z=-5.32, p<0.001, respectively). These findings supported that the platelet indices could be influenced by T. pallidum infection.
Figure 3Comparison of PLT(A), MPV(B), and PDW(C) before and after anti-treponemal therapy. Differences between groups were analyzed by paired-samples Wilcoxon signed-rank test. The red lines showed the medians. The value of p<0.05 was considered significant.
The PLT, MPV, and PDW were associated with the parameters related with disease activities of syphilis.
To investigate the correlation of platelet indices with disease activities of syphilis, including the syphilis activity indicators (RPR titer, CSF-WBC count, CSF protein, and CSF-VDRL titer) and the inflammatory indicators (WBC, ESR, and CRP), spearman correlation analyses were conducted. As shown in Table 2, PLT was negatively correlated with MPV and PDW (r=-0.33, p<0.001; r=-0.24, p<0.001). In addition, there was a positive correlation between PDW and MPV (r=0.42, p<0.001). PLT was positively correlated with all syphilis activity indicators (RPR titer, CSF-protein, CSF-WBC count, and CSF-VDRL) and all inflammatory markers (WBC, CRP, and ESR). On the contrary, PDW was negatively correlated with all of these parameters, whereas MPV was only inversely associated with RPR titer, ESR, and CRP.
Table 2Evaluation of the correlation between PLT, MPV, PDW, and other parameters in syphilis
PLT, × 103/μL
MPV, fL
PDW, fL
r
p
r
p
r
p
PLT, × 103/μL
-
-
-0.33
<0.001
-0.24
<0.001
MPV, fL
-0.33
<0.001
-
-
0.42
<0.001
PDW, fL
-0.24
<0.001
0.42
<0.001
-
-
serum RPR titer
0.23
<0.001
-0.19
0.008
-0.21
<0.001
CSF-WBC, cells/μL
0.14
<0.001
-0.03
0.190
-0.22
<0.001
CSF-protein, g/L
0.11
<0.001
-0.01
0.970
-0.24
<0.001
CSF-VDRL titer
0.18
<0.001
-0.01
0.78
-0.20
<0.001
WBC, μL
0.29
<0.001
-0.032
0.300
-0.15
<0.001
ESR, mm/h
0.11
<0.001
-0.12
<0.001
-0.28
<0.001
CRP, mg/L
0.14
<0.001
-0.13
<0.001
-0.30
<0.001
Spearman correlation analysis was performed to investigate the correlations of platelet indices (PLT, MPV, and PDW) with related parameters (WBC, ESR, CRP, RPR, CSF-WBC, CSF-protein, and CSF-VDRL). p <0.05 were considered statistically significant.
Syphilis is a mysterious disease. Up until now, there are too many unknowns, including how T. pallidum invades the organs, how it actively damages the tissue, why syphilis can be in a latent state, and when and where the disease turns active and destroys our body again. Therefore, knowing the factors associated with disease activities is of great importance for the clinical management of syphilis. In this study, we comprehensively described the whole picture of platelet indices in all stages of syphilis and analyzed the relationship between disease activities and platelet indices in patients with syphilis. Our findings revealed that PLT was significantly increased in patients with primary and secondary syphilis, and it was positively associated with the serum RPR titer, WBC, CRP, and ESR, as well as CSF-protein, CSF-WBC, and CSF-VDRL, whereas MPV and PDW were dramatically decreased in patients with syphilis with all stages; both of them were negatively associated with these parameters. As reported previously, serum RPR titer, CSF-VDRL titer, and CSF-WBC are well-known indicators of disease activities in syphilis (
Evaluation of platelet count, erythrocyte sedimentation rate and C-reactive protein levels in paediatric patients with inflammatory and infectious disease.
). On the basis of our results and previous studies, we have reasons to believe that platelet indices may be involved in the disease progression of syphilis.
Platelets are anucleate disk-shaped cells derived from megakaryocytes and play a vital role in pathophysiological conditions such as thrombosis, stroke, and infections (
). Platelet parameters, including MPV, PDW, and PLT, are easy and inexpensive to be measured. MPV and PDW are believed to be the indices of platelet activation. PLT is inversely related with MPV and PDW under both physiological and pathological conditions to keep homeostasis and sustain a constant platelet mass (
). In the present study, PLT was negatively correlated with MPV and PDW. This inverse relationship during T. pallidum infection might be due to a dysfunctional immune system or increased circulating concentrations of thrombopoietin (TPO) released by megakaryocytes stimulated by T. pallidum (
The mechanism of PLT increase upon infection has not been fully elucidated. It has been shown that cytokines, including interleukin-1 (IL-1), interleukin-3 (IL-3), interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), granulocytes and macrophage colony-stimulating factor (GM-CSF), and TPO participate in the modulation of the megakaryocytes/platelet production and the regulation of platelet size in inflammatory conditions (
). Infection of respiratory syncytial virus (RSV) often results in secondary thrombocytosis, which was thought to be caused by the increased levels of IL-6 and IL-8 (
); however, we did not verify whether the condition resulted in the increase of PLT. In the present study, PLT was significantly increased in primary and secondary syphilis but not in other syphilis stages. Previous studies indicated that IL-6, TNF-α, and IL-1β were elevated in patients with syphilis, especially in patients with primary and secondary syphilis (
). As such, we speculated that the increase of PLT in our cases might be attributed to the changes of the cytokines above. In addition, studies showed that the CRP levels are positively correlated with TPO concentrations (
), and it was positively correlated with PLT, indicating that the increased PLT in our cases is also probably because of the elevated CRP level.
MPV and PDW are the indices of platelet activities. Differential alternation direction of MPV and PDW in several chronic inflammatory diseases has been reported, such as psoriasis, inflammatory bowel disease, and lupus nephritis (
). MPV and PDW were increased in infective endocarditis, ascitic fluid infection, and COVID-19, whereas decreased MPV and PDW were reported in adult tuberculosis during disease exacerbation and HIV infection (
The evaluation of platelet indices and markers of inflammation, coagulation and disease progression in treatment-naïve, asymptomatic HIV-infected individuals.
). However, the mechanisms of why MPV and PDW increased or decreased in those infectious diseases remain unknown. To our knowledge, this is the first report to show that the MPV and PDW were decreased in patients with syphilis with all stages, although the underlying mechanisms remain to be explored. Researches have shown that IL-6, IL-1, TNF-α, M-CSF, and G-CSF could modulate platelet size in ongoing inflammatory diseases, especially cytokine IL-6 (
). Thus, if the decreased MPV and PDW in our cases were contributed to the elevated IL-6 and TNF-α, it is worthy of further study. Besides, research showed that in patients with persistent infection, large-sized platelets migrated to the inflammatory sites and increased the consumption of large-sized platelets (
). Because syphilis is a chronic, systemic disease, the decrease of MPV and PDW can also be caused by the overconsumption of large-sized platelet during the disease course.
In conclusion, our study provides the first evidence that platelet indices are associated with the disease activities in patients with syphilis. As the alternation of platelet indices reflects the alternation of function, this study may suggest the foundation for further elucidation of the underlying mechanism of how platelets participate in the inflammatory response and pathogenesis of syphilis.
Acknowledgments
We are grateful for all the participants of this study, and we greatly appreciate the clinical staff who recruited patients.
Funding
This work was supported by the National Natural Science Foundation of China (grant numbers 82072322 and 82172319) and Shanghai Science and Technology Commission (grant number YZDX20193100002868).
Ethical Approval
This study was approved by the Ethics Committee of the Shanghai Skin Disease Hospital (approval no. 2020-16).
Conflict of interests
The authors declare that no conflicts of interest exist.
References
Brinker MR
Macek J
Laughlin M
Dunn WR.
Utility of Common Biomarkers for Diagnosing Infection in Nonunion.
The evaluation of platelet indices and markers of inflammation, coagulation and disease progression in treatment-naïve, asymptomatic HIV-infected individuals.
Evaluation of platelet count, erythrocyte sedimentation rate and C-reactive protein levels in paediatric patients with inflammatory and infectious disease.
p<0.05 were considered statistically significant.
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