Diagnosis of chronic prostatitis by noninvasive methods in elderly patients with benign prostatic hyperplasia in China

Chronic prostatitis is hard to be identified in BPH patients in clinical works. This study aimed to diagnose chronic prostatitis in BPH patients by noninvasive methods. BPH patients who received transurethral resection of prostate from January 2014 to July 2015 were enrolled in current study. Patients were received examinations of PSA, sex hormones, inflammatory cytokines, metabolic panel and transrectal ultrasonography. According to histological results, patients were divided into two group of BPH with/without prostatitis. Logistic regression was used to find risk factors of chronic prostatitis. As a result, 181 men with an average age of 72.15 ± 8.41 years were enrolled in this study, including 116 patients with prostatitis and 65 patients without prostatitis. The storage sub‐score, PSA and IL‐2R were significantly higher in patients with prostatitis than those without prostatitis. Based on logistic regression analysis, the above three parameters were also the risk factors of BPH with prostatitis. The diagnostic model was calculated as: 0.317 × storage sub‐score + 0.092 × PSA + 0.003 × IL‐2R − 4.296. The AUC was 0.725. Histological prostatitis in BPH patients can be diagnosed by the combination of serum IL‐2R, PSA and storage sub‐score. Identification of chronic prostatitis in BPH patients could more efficiently alleviate urinary symptoms and reduce the risk of disease progression.

great extent. Furthermore, the existence of inflammation in prostate made α1-blockers and 5α reductase inhibitors (5-ARIs) insufficient to improve the urinary symptoms (Ficarra et al., 2014). The objective of the current study is to analyse the efficacy of noninvasive methods in diagnosis of chronic prostatitis in BPH patients.

| Patients enrolment and evaluation
This retrospective study was carried out on the BPH patients who re-  IPSS consists of seven questions, and all patients were required to complete the questions independently. The storage sub-score was the sum of question 2, question 4 and question 7 while the voiding sub-score was the sum of question 3, question 5 and question 6. In addition, fasting blood sample for analysis of prostate-specific antigen (PSA), free PSA (fPSA), serum inflammatory cytokines (interleu- Meanwhile, patients received transrectal prostate ultrasonography (TRUS), through which ultrasonic images were obtained with the patient in the left decubitus position. Total prostate volume (TPV), transitional zone volume (TZV) and intravesical prostatic protrusion (IPP) were measured by a certified ultrasonologist. All the patients were subsequently underwent TURP. During TURP, deep random tissue specimens (weighing 1-2 g) were collected under sterile conditions through resectoscope and transported to pathology laboratory in sterile saline. The specimens were then fixed in 10% neutral-buffered formalin and embedded in paraffin following routine histologic procedures. Tissue sections (5 μm) were stained with haematoxylin and eosin. Inflammatory cell infiltration in the glandular and/or stromal was defined as prostatitis by an experienced pathologist.

| Statistical analysis
The data were analysed by Statistical package for social science, version 21.0. Results were presented as mean ± SD. Independent t test was used to evaluate the numerical parameters of the two groups for statistic difference when the parameter was consistent with normal distribution and Mann-Whitney U test was used when the parameter was consistent with nonparametric distribution. Multivariate logistic regression was used to identify the risk factor of chronic prostatitis in BPH patients. For all statistic tests, p < .05 was considered to be statistically significant.

| RE SULTS
A total of 181 patients were recruited in our study and the mean age was 72.15 ± 8.41 years old. According to the pathological results, 116 patients were diagnosed with histological prostatitis while 65 patients showed no pathological prostatitis. Table 1 showed the comparison of clinical parameters and serum examination results between BPH patients with prostatitis and BPH patients without prostatitis. Serum PSA level (8.23 ± 7.69 vs. 4.92 ± 3.84, p = .005), serum IL-2R level (531.96 ± 200.75 vs. 434.11 ± 153.54, p = .001) and storage sub-score (9.24 ± 1.55 vs. 8.52 ± 1.63, p = .009) in the prostatitis group were significantly higher than those in BPH alone group. The other results between two groups had no significant difference. Table 2 showed the results of multivariate logistic regression.

| D ISCUSS I ON
The diagnosis of chronic prostatitis in BPH patients is of great clinical significance. The first reason is that long-term inflammation in prostate tissue may have association with malignant tumour (Sfanos et al., 2018), though it is still controversial until now. Approximately 20% of human malignant tumours can be caused by chronic inflammation or chronic infection (Mantovani et al., 2008). The prostate cancer prevention trial (PCPT) is the first prospective study to assess the relationship between inflammation and the occurrence of prostate cancer in men without biopsy indications. This study confirmed that inflammation in benign tissues at the time of initial biopsy is positively correlated with the later development of prostate cancer (Platz et al., 2017). In addition, the hypothesis that inflammatory reaction could lead to cancer has also been confirmed in the adult animal model (Prins et al., 2006).
The second reason is based on the hypothesis founded by several studies that inflammation is an obstacle to effective treatment in BPH patients. Roehrborn (2008) concluded that chronic prostatitis played an important role in promoting disease progression and increasing the risk of acute urinary retention in benign prostatic hyperplasia. Moreover, 5-ARIs may lose their efficacy upon chronic inflammation. Presence of inflammation in prostate is able to stimulate IL-6 and IL-8 production which could activate androgen receptors without dihydrotestosterone (DHT), as well as increase releasing in growth factors. Therefore, lymphocyte infiltration could maintain prostate cell proliferation despite the presence of 5-ARIs (Ficarra et al., 2014). Additionally, the efficacy of α1-blocks may also decrease in the condition of prostatitis. Α1adrenoceptors and some inflammatory mediators such as thromboxane A2 (TXA2) share common intracellular mediators to induce smooth muscle contraction in the prostate (Christ and Andersson, BPH without prostatitis (n = 65) (mean ± SD) BPH with prostatitis (n = 116) (mean ± SD) Abbreviations: BPH, benign prostatic hyperplasia; CP, chronic prostatitis; Cr, creatinine; FSH, follicle-stimulating hormone; Glu, fast blood glucose; HbA1c, glycohemoglobin; HDL, high-density lipoprotein; IL, interleukin; IPP, intravesical prostatic protrusion; IPSS, international prostate symptom score; LDL, low-density lipoprotein; LH, Luteinising hormone; P, progesterone; PSA, prostate-specific antigen; T, testosterone; TC, cholesterol; TG, Triglyceride; TNF, tumour necrosis factor; TPV, total prostate volume; TZV, transitional zone volume. In the current study, the prevalence of chronic prostatitis in BPH patients was 64.09% (116/181 patients), which was similar to that in Morote's study (68.3%) (Morote et al., 2000). The established model to diagnose chronic prostatitis in BPH patients was composed of serum PSA level, storage sub-score and serum IL-2R level. As mentioned above, The PSA release is elevated due to the activation of androgen receptors stimulated by inflammatory cytokines (Ficarra et al., 2014). The study of Agnihotri et al. (2014) suggested that significant inflammation of the prostate resulted in spurious rise in serum PSA level. This conclusion was also confirmed in young men (Korrovits et al., 2011). Effective treatment for prostatitis could significantly reduce serum PSA level in ageing men (Toktas et al., 2013).
Therefore, relatively high serum PSA level is an important manifestation of chronic prostatitis in BPH patients.

The data from the Reduction by Dutasteride of Prostate Cancer
Events (REDUCE) trial showed the evidence of a relationship between the degree of lower urinary tract symptoms (LUTS) and the degree of chronic inflammation. IPSS score, especially storage subscores were obviously higher in the group of patients with histological chronic inflammation compared with those without chronic inflammation (Nickel et al., 2008). In our study, the storage subscores of the patients with chronic prostatitis were significantly higher than those without prostatitis, which was similar to the result of REDUCE trial. However, no significant difference was detected between two groups in regards to IPSS and voiding sub-score in this study, which was probably due to the different timing of IPSS collection. The data of REDUCE trial were collected before medical intervention while the data of patients in our study were collected after medical treatment. The result of our study suggested that medical treatment for BPH alone could relieve voiding symptoms but not storage symptoms.  et al. (2000). Several studies revealed that IL-8 may be a reliable biomarker of inflammation in BPH patients because its level was significantly higher in both seminal plasma and expressed prostatic secretion (EPS) in BPH patients with chronic prostatitis (Liu et al., 2009;Penna et al., 2007). However, seminal IL-8 level was associated with not only prostatitis, but also inflammation in other organs, such as seminal vasculitis and epididymitis. In addition, seminal IL-8 level was also closely related to prostate cancer.  (Lotti and Maggi, 2013). All of the above greatly limit the diagnostic value of seminal IL-8 level in BPH patients with prostatitis.
IL-2 is a pleiotropic cytokine which can promote the growth of T cells, enhance the activity of NK cell lysis, induce regulatory Tcell differentiation, mediate activation and induce cell death, and plays a key role in immune response (Liao et al., 2013). IL-2 activated lymphocytes increased the number of membrane-bound IL-2R. In the meantime, they release a soluble form of interleukin-2 receptor (sIL-2R) into blood. The role of sIL-2R is to bind excess IL-2 and release it later. B and T lymphocytes are activated in this process. They can subsequently activate the production of interleukin, interferon and tumour necrosis factor, and stimulate the cytotoxic cells and lymphokine activated killer cells, as well as the cytotoxicity of macrophages (Engelhardt et al., 2014). In our study, serum IL-2R levels (soluble IL-2R) were significantly higher in BPH patients with chronic prostatitis. It indicates that inflammatory cells were activated by IL-2 to participate in the inflammatory response, which is consistent with the infiltration of lymphocytes, monocytes and plasma cells in the histology of chronic prostatitis. Moreover, Poutahidis et al. (2009) found that there was also a higher expression of IL-2 in prostate cancer, which further confirmed the relationship between prostatitis and prostate cancer.  (Martin et al., 2015). However, up to now, the consistence of serum IL-2R and semen or urine IL-2R has not been reported, in which further investigation is needed.
AUC of the diagnostic model established by us was 0.724. The sensitivity and specificity were considered fair, which may be related to the small sample size in our study. However, the optimal PPV was up to 78.4%, which meant approximately 80% of the patients diagnosed with chronic prostatitis by the current model were really suffered from prostatitis diagnosed by histological results. The accuracy rate would be considered satisfactory for both urologists and patients on condition that the model has been validated in other studies.
The limitation of this study is that the prostatitis was not classified according to the grading system. Further multicentre study will be carried out to establish a more accurate model.
In conclusion, the model consisting of serum PSA level, serum IL-2R and storage sub-score could assist in diagnosing chronic prostatitis from BPH patients. Identification of chronic prostatitis among patients with BPH is beneficial for medical decisions, which can more efficiently alleviate urinary symptoms and reduce the risk of disease progression.

ACK N OWLED G EM ENTS
The authors thank all the patients who participated in this study.

CO N FLI C T O F I NTE R E S T
The authors declare that they have no competing interests.

DATA AVA I L A B I L I T Y S TAT E M E N T
Data available on request from the authors. The data that support the findings of this study are available from the corresponding author upon reasonable request.