Corticomotor excitability of the pelvic floor muscles in females: Characteristics of motor evoked potentials and test-retest reliability

Abstract

Objectives: To (1) design an efficient TMS protocol to elicit motor evoked potentials (MEPs) from female pelvic floor muscles (PFMs), (2) describe the characteristics of PFM MEPs and silent periods (SPs), (3) compare PFM MEP characteristics with nearby muscles and (4) determine the test-retest reliability of PFM MEP characteristics and SP duration.

Methods: Through a cross-sectional, observational design, adult females were tested at two sessions separated by one week. Single-pulse TMS was delivered over the motor cortex and motor responses were recorded from three PFMs, the lateral abdominal wall (LAW) and the hip adductors (ADD). MEP characteristics were compared among the PFMs and with those from the ADD and LAW. Test-retest reliability was examined using intra-class correlation coefficients (ICCs).

Results: Nearly all participants (n = 40/41) exhibited measurable SPs in the pubovisceralis and at least one other PFM. PFM MEPs exhibited shorter onset latencies than those of ADD and LAW. ICCs ranged from good to excellent, except for peak latency, which was poor. Yet all measures displayed high between-participant variance.

Conclusion: Investigating reliable TMS-induced motor responses in the PFMs of females is achievable using our protocol.

Significance: Our findings highlight the possibility of extending TMS applications to investigate changes in corticomotor excitability that may contribute to conditions that are associated with high PFM tone, such as vulvovaginal pain.

Keywords: Bulbocavernosus; Corticomotor excitability; Levator ani; Overactivity; Pain; Pelvic floor muscle; Pubovisceralis; Tone; Transcranial magnetic stimulation; Vulvodynia.