Novel insights of vulvodynia pathophysiology from reliable and comprehensive pelvic floor muscle surface electromyography characterization: can it help predict response to botulinum toxin treatment?

[BACKGROUND] Findings on vulvodynia-associated alterations in the pelvic floor muscles' (PFMs') myoelectrical activity are contradictory, and no study has yet assessed whether they influence treatment outcomes.

[AIM] To characterize vulvodynia-associated alterations in PFM activity and assess its potential to predict the response to botulinum toxin type A (BoNT/A) treatment.

[METHODS] This prospective, non-masked, and non-randomized study recruited 35 vulvodynia patients who underwent BoNT/A injections and 35 healthy women. Their left and right PFM activity was monitored by surface electromyography (sEMG) with 2 recording modalities (intravaginal probe and external electrodes) during PFM contractions and rest and compared across groups at baseline. Clinical information was also collected from their medical history, pelvic physical examination, and self-informed clinical questionnaires. Both sEMG and clinical features were used to predict the patient's response to treatment using multiple binary logistic regression models.

[OUTCOMES] sEMG signals' root mean square (RMS), median frequency (MDF), sample entropy (SampEn), intramuscular and intermuscular magnitude-squared coherence (mscoh) and imaginary part of their coherency (iCOH), and clinical outcomes (sociodemographic, obstetric, gynecological, urological, and other general clinical characteristics; painful comorbidities; pelvic and vulvar pain sensitivity; Patient's Global Impression of Improvement).

[RESULTS] Vulvodynia patients exhibited significantly lower intensity during contractions (<RMS, P = .003) and altered intramuscular coupling (>mscoh) during contractions (P = .004) and rest (P = .006) in the myoelectrical activity of their left superficial PFM (sEMG from external electrodes) and altered intermuscular coupling during contractions (>mscoh, P = .004) in their deep PFM (sEMG from intravaginal probe) than healthy women. Furthermore, intramuscular coupling at rest was significantly associated with response to treatment (P < .01) and predicted it accurately when combined with clinical information (AUC = 0.95).

[CLINICAL IMPLICATIONS] PFM sEMG can provide valuable insights into vulvodynia pathophysiology and help optimize treatment selection, potentially reducing the economic and psychological impact of ineffective treatment.

[STRENGTHS AND LIMITATIONS] This study provides a reliable and comprehensive description of PFM myoelectrical activity alterations in vulvodynia conditions, demonstrating for the first time that sEMG information can improve the prediction of treatment response. It is limited by a small sample size of intravaginal probe recordings due to pain elicited by probes during their insertion and signal quality.

[CONCLUSION] Vulvodynia is associated with decreased activity intensity in the superficial PFM and altered electrical coupling, as shown by sEMG, which can enhance the precision of BoNT/A treatment response prediction and thus reduce the economic and psychological burden of ineffective treatment.