**5. Conclusions**

For the first time in the case of UPS, the layered structure of the urethral wall was investigated in vivo using CP OCT to assess some of the pathogenetic aspects of the development and progression of this disease. The CP OCT method covers the range of possibilities of traditional cystoscopy and allows information to be obtained about the state of the urethral tissues that cannot be adequately assessed during cystoscopic examination alone. The predominant changes in the tissues of the urethra are fibrosis of the subepithelial structures and trophic changes in the epithelial layer. In 68.8% of cases, the "behavior" of the tissues of the proximal segmen<sup>t</sup> of the urethra coincided with changes in the bladder neck. The importance of the in vivo acquisition and operative analysis possible with CP OCT in combination with TVUS/compression US data in patients with UPS is beyond doubt.

Deep objective analysis of tissues can reveal the basis of pathogenesis. Real-time visualization of structural changes in the tissues of the urethra (epithelium, connective tissue, muscle layer, vasculature, and paraurethral glands) is important because it influences the final diagnosis, understanding of the pathogenesis of the disease and treatment tactics. An analysis of the comorbidities of patients with UPS showed that inflammatory gynecological diseases can become a premorbid background/one of the triggering mechanisms for the development of UPS.

**Author Contributions:** Conceptualization, O.S. and E.K.; methodology, E.T.; software, M.S.A.M.M. and V.L.; investigation, O.S., A.K., M.S.A.M.M., S.Z., and E.T.; data curation, V.L.; writing—original draft preparation, O.S., A.K., E.K., and S.Z.; writing—review and editing, O.S., A.K., and E.K.; funding acquisition, O.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was funded by Russian Foundation for Basic Research, gran<sup>t</sup> number 19-07-00395.

**Acknowledgments:** The authors would like to thank Grigory V. Gelikonov and Valentin M. Gelikonov (Institute of Applied Physics of the RAS, Russia) for the provision of the CP OCT device and its technical support during the research.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
