F. Ignácio Antônio1, M. Petter Rodrigues2, M. Vandermolen3, F. Tremblay1, C. Pukall4, L. McLean1
1University of Ottawa, School of Rehabilitation Sciences, Ottawa, Canada, 2Universidade Federal do Rio Grande do Sul, Obstetrics and Gyneacology, Porto Alegre, Brazil, 3University of Ottawa, Department of Mechanical Engineering, Ottawa, Canada, 4Queen’s University, Department of Psychology, Kingston, Canada
Background: Corticomotor excitability can be assessed through motor evoked potentials (MEPs) elicited by transcranial magnetic stimulation (TMS). While TMS has been used extensively to probe the distal extremity musculature, very little effort has been made to explore the more proximal motor representations, notably those of the pelvic floor muscles (PFMs).
Purpose: To determine, in female participants, whether MEPs elicited from the PFMs can be differentiated from those elicited from nearby lower limb muscles and to determine whether TMS measures derived from the PFMs, including MEP amplitude and latency and cortical silent period (cSP), are reliable on repeated testing.
Methods: Participants consisted of 27 healthy female adults (30±7 years; pregnancy, menopause, and gynecologic conditions excluded). Participants attended two laboratory-based assessments within one week. At each session, participants were instrumented with surface electrodes over the PFMs [puboviscelaris(PV), bulbocavernosus(BC) and external anal sphincter(EAS)], the lateral abdominal wall (LAW), tibialis anterior (TA) and adductor longus (ADD). Resting motor threshold (rMT) was determined using TA as the target muscle. Twelve MEPs were obtained at rest and six during PFM contraction by delivering single TMS pulses at 130% rMT to the vertex using a double cone coil. MEP characteristics (amplitude and latency) were obtained for all muscles at rest and during PFM contraction, while cSPs were determined only for the PFMs. The reliability of TMS measures, including MEP amplitude, latency and cSP, was evaluated using intra-class correlation coefficients (ICCs, model II), rated as poor (ICC≤0.40), fair (0.40<ICC≤0.59) good (0.60< ICC≤0.74) and excellent (ICC≥0.75).
Results: PFM MEPs were successfully elicited in all participants. At rest, mean(±SD) MEP latency for the PFMs was 6.8(±8.5)ms shorter than ADD and 11(±0.2)ms shorter than TA, but was not different from the LAW. During PFM contraction, the latency difference to the PFM MEPs was a mean of 1.4(±0.3)ms shorter than at rest, while for the LAW it was not [-4(±2.5)ms]. ICCs for PFM MEP latency both at rest and during PFM contraction indicated fair to good reliability, MEP amplitudes showed poor to good reliability at rest, and fair to good reliability during contraction. The cSP duration showed excellent between-day reliability for all PFMs (0.75<ICC<0.85).
Conclusion(s): These results show that MEPs can be elicited from the PFM representation in response to TMS at the vertex. PFM MEPs typically exhibited shorter onset latency from those elicited from nearby thigh or leg muscles, but latency measures tended to vary on repeated testing. Such variability in latency could reflect the more diffuse and less secure synaptic connections established by corticospinal projections to the PFMs when compared to more distal limb muscles. On the other hand, the fact that the cSP duration proved to be a reliable measure suggest that this index might be more suitable to probe corticomotor excitability to the PFMs.
Implications: TMS can be used to probe changes in the corticomotor excitability of pelvic floor motor representation. In this regard, cSP duration might be a good index to assess changes related to dysfunctions linked with pelvic floor conditions in females.
Funding, acknowledgements: Funding for this work was provided by operating grants to Dr. McLean from the NSERC and from the CIHR
Keywords: Corticomotor excitability, pelvic floor muscle, transcranial magnetic stimulation
Topic: Pelvic, sexual and reproductive health
Did this work require ethics approval? Yes
Institution: University of Ottawa
Committee: University of Ottawa - Office of Research Ethics and Integrity
Ethics number: H-01-19-2368
All authors, affiliations and abstracts have been published as submitted.
