Electromyographic/Somatosensory Evoked Potential Monitoring During Sacral Neuromodulation

Abstract

Sacral root neuromodulation has been employed for the treatment of idiopathic overactive bladder, fecal incontinence, urgency-frequency syndromes, interstitial cystitis, pudendal neuralgia, vulvodynia, coccygodynia, and a variety of chronic pelvic pain (CPP) syndromes. A direct, single root stimulation device received U.S. Food and Drug Administration (FDA) approval for the treatment of urinary urgency and frequency, urinary incontinence in 1997, and urinary retention in 1999, but many centers have had more success with retrograde longitudinal placement within the spinal canal. The ventral rami of S2–4 provide innervation of the pelvis. The S3 sacral level contributes to the innervation of the anterior perineal muscles, making it the most frequent target in treatment of pelvic dysfunction and a typical target for the single root percutaneous device. These portions of the nervous system have traditionally been very difficult to target with traditional methods over the dorsal columns in the spinal cord. The conus medullaris is a highly mobile structure, which is nearly enveloped in the nerve roots of the cauda equina. Accordingly, placement of epidural stimulating electrodes over the conus has traditionally been plagued by extreme variability in the effects of stimulation, not only from patient to patient but also in the same patient over time. At the conus level, the dorsal cerebrospinal fluid layer is relatively thick and serves as an insulator for the spinal cord; the conus is very mobile, which increases the risk of lead migration, and finally, owing to the presence of large afferent fibers, the sacral stimulation may produce undesired paresthesia in additional regions.