(088) CONTRALATERAL SYMMETRY IN THE TOPOGRAPHY OF SELF-REPORTED VULVAR PAIN
Authors: Bittoni C , Kiesner J , Komisaruk B 
Published: June 2024

Abstract

Introduction
Vulvar pain is a transdiagnostic symptom that is associated with diverse end organs, neurological, and musculoskeletal mechanisms. A better understanding of the neural mechanisms behind the spreading/worsening of vulvar pain across different sites on the vulva, could guide future research, classification, and treatment of vulvar pain-related conditions.

Objective
Examine the topographic correlations of vulvar pain and provide insights regarding the involvement of neural pathways underlying the topographic distribution of such pain.

Methods
Self-reports of sexual and genital health were collected from 2199 women through online questionnaires, as part of a larger study. Efforts were made to recruit a heterogenous sample, oversampling for women with genito-pelvic pain. Participants were asked about the presence and location of vulvar and/or vaginal pain. In addition, participants were asked about history and types of non-genital injuries. If a participant reported chronic vulvar pain, they were then presented with a drawing of a vulva divided into 24 areas, asking them to indicate the location(s) of their pain (localization of vaginal pain not included). Correlations were conducted on the presence of pain across vulvar areas that were contralaterally distributed (horizontal) vs spatially close but ipsilaterally distributed (vertical and radial), and distinguishing between women with vs without a history of back and/or pelvic injury.

Results
911 women reported experiencing chronic vulvar or vulvar-vaginal pain. Results from correlations across vulvar areas are reported in Figure 1, 2 and 3, distinguishing between women with and without a history of back/pelvic injury. In both groups, horizontal correlations across left and right sides of the same tissue/structure were the strongest (Figure 1), whereas areas that were spatially close on the ipsilateral side (vertical and radial) showed weaker correlations (Figures 2 & 3). Statistical tests confirmed differences in correlations both between-groups and within-groups, across different spatial relations (horizontal, vertical, radial).

Conclusions
The observed pattern of topographic correlations suggests specific constraints on the mechanisms involved in the spreading of vulvar pain, showing a horizontally symmetrical distribution of correlations (within tissue/structure), as opposed to a proximity-based distribution of correlations. This appears to reflect symmetrically contralateral sensitization within the same structure, even if the areas were relatively distant (e.g., right and left labia minora). According to our results, this applies more to women without a history of back/pelvic injury, compared to women with a history back/pelvic injury. Consistent with past research showing that a temporary nociceptive stimulus induces hyperalgesia and allodynia in the ipsilateral and symmetrically contralateral site of noxious stimulation (Shenker et al.,2008), our results suggest that similar neural mechanism(s) might be involved in chronic vulvar pain. The pattern of correlations found could be mediated by chronic pain-induced activation of the commissural fibers that connect, and perhaps sprout into, the symmetrically contralateral sides at the level of the dorsal horn. This would constitute a form of central sensitization (Latremoliere & Woolf, 2007). Whether a comparable central sensitization process also occurs at the level of the sensory cortex (or other brain regions), or whether different forms of synaptic potentiation at the neural level are involved, must also be considered.

Disclosure
Any of the authors act as a consultant, employee or shareholder of an industry for: Adamo Bioscience.