Is Pelvic Pain Severity Correlated With Nerve Fiber Density Within DIE Nodules?

Deep infiltrating endometriosis (DIE) is a highly symptomatic phenotype of endometriosis that invades retrocervical, parametrial, rectovaginal, bowel, and other pelvic structures, and is frequently associated with severe dysmenorrhea, dyspareunia, dyschezia, dysuria, and chronic pelvic pain. Emerging evidence suggests that DIE nodules harbor abundant nerve fibers and may show perineural involvement, yet the relationship between intranodular nerve fiber density and patient-reported pelvic pain has not been defined with sufficient clinical granularity.

This retrospective, cross-sectional study with prospective pathology re-review investigates whether nerve fiber density within surgically excised DIE nodules correlates with the intensity and localization of pelvic pain. Eligible participants are women (18-55 years) operated for DIE after inadequate response to medical therapy (e.g., nodule excision, nerve-sparing hysterectomy ± salpingo-oophorectomy, ovarian surgery, and/or bowel resection when indicated). Demographic characteristics, obstetric/gynecologic history, prior surgeries and medical treatments, and standardized pain assessments (visual analogue scale [VAS] scores for dysmenorrhea, dyspareunia, dyschezia, dysuria, and chronic pelvic pain) are abstracted from the hospital information system.

All resected specimens are routinely fixed in buffered formalin and processed for histopathology. For this study, archived blocks from endometriotic foci are recut (3-µm sections) and stained with hematoxylin-eosin and immunohistochemically labeled with SOX-10 to visualize neural elements. Under ×200 magnification, the number of SOX-10-positive neural profiles within endometriotic foci is quantified, and mean nerve fiber counts (per evaluated field/area) are calculated to derive a nerve fiber density metric for each nodule. The primary endpoint is the association between nodule-level nerve fiber density and pain severity/localization. Secondary endpoints include associations with clinicopathologic variables (lesion site and depth, parametrial/rectovaginal/bowel involvement), and exploratory analyses of indices that may discriminate patients with severe pain.

Statistics will be performed with SPSS (v23). Categorical variables are summarized as n (%) and compared with χ² or Fisher's exact tests; continuous variables as mean ± SD (or median [min-max]) and compared with Student's t-test or Mann-Whitney U test as appropriate; within-group paired comparisons may use the Wilcoxon test. Two-sided p < 0.05 denotes statistical significance. Because this is a retrospective audit with predefined time frame and all-comer surgical inclusions, no formal sample size calculation is planned.

Risks/Benefits: This is minimal-risk research using archived pathology and existing clinical records; no additional procedures or changes to care are required. Results may clarify whether tissue-level neural metrics in DIE nodules reflect the patient's pain phenotype, potentially informing counseling, surgical planning (e.g., nerve-sparing strategies), and the development of response biomarkers for future prospective studies.