Pelvic floor muscle activation in response to pressure stimuli applied to the vulvar vestibule: an observational study comparing women with and without provoked vestibulodynia.

Background: The nature of pelvic floor muscle (PFM) involvement in provoked vestibulodynia (PVD) is poorly understood.

Aim: We aimed to determine if PFM electromyographic (EMG) activity in anticipation of or response to pressure applied to the posterior vaginal fourchette differs between those with and without PVD, and if the magnitude of PFM response is associated with pressure pain sensitivity, psychological or psychosexual function.

Methods: This was an observational case-control study. Forty-two volunteers with PVD and 43 controls with no vulvar pain participated. Five on-line questionnaires were completed, then participants underwent a laboratory-based evaluation of vulvar pain sensitivity. EMG activation of the PFMs, hip adductor, and upper trapezius muscles was measured before, during, and after pressure stimuli (low, moderate) were applied, in random order, to the posterior vaginal fourchette and the posterior thigh (control site).

Outcomes: EMG amplitude of the pubovisceralis (PV), bulbocavernosus (BC), and external anal sphincter (EAS) muscles. Secondary outcomes were EMG activation of the hip adductor brevis and upper trapezius muscles, questionnaire scores reflecting psychological/psychosexual outcomes, pressure pain threshold (PPT) at the vulvar vestibule, pain reported on a tampon test, and heart rate/heart rate variability.

Results: Compared to controls, EMG activation of the PV and EAS, but not the BC, was higher in anticipation of the pressure applied to the vaginal fourchette, was higher in all PFMs while the pressure was applied, and remained higher than baseline after the pressure was removed among those with PVD. EMG response amplitudes were modulated by the intensity of the pressure applied, with the largest responses reaching over 40% MVC in the EAS among those with PVD. PFM EMG amplitudes were associated with greater pain sensitivity and lower sexual function, but not with pain catastrophizing, central sensitization, depression, anxiety, or stress.

Clinical implications: While some anticipatory activation was observed, EMG responses were primarily observed during and after the application of the pressure. Among those with PVD, digital assessment of PFM tone might reflect PFM responses to pain at the vulvar vestibule, and interventions to reduce local pain sensitivity may be an important first step to successful improvements in vaginal function.

Strengths and limitations: This study includes a robust analysis of EMG activation. However, the cross-sectional design precludes the determination of causal relationships.

Conclusions: Those with PVD demonstrate higher PFM responses and a higher prevalence of anticipatory activation in the PV and EAS muscles than controls in response to pressure applied at the vulvar vestibule.