Motor evoked potentials from the striated urethral sphincter and puborectal muscle: reproducibility of latencies

OBJECTIVE: Transcranial magnetic stimulation can be used to test the motor efferents to the pelvic floor muscles. The aim of the present study was to assess the long-term test-retest reproducibility of pelvic floor MEPs.

METHODS: Eighteen healthy women without evidence of neurological or lower urinary diseases had serial measurements of pelvic floor MEPs with a mean test-retest interval of 39 weeks. Cortical and spinal transcutaneous magnetic stimulations were applied. Evoked potentials were recorded with concentric needle electrodes placed in the striated urethral sphincter and the puborectal muscle by a transvaginal route. Responses from the abductor hallucis were also recorded for comparison. Stimulations were performed with relaxed pelvic floor and with tonic contraction (facilitated responses). Student's t test was applied and mean latencies were plotted against differences to analyze test-retest variability.

RESULTS: There were no systematic effects of time or other variables that might differ between trials for all subjects. However, the means vs. differences plots revealed a large scatter of intra-individual test-retest values. The poor reproducibility was common for all tested pelvic floor muscles and modalities.

CONCLUSIONS: The clinical use of pelvic floor MEPs is questionable.