Translumbar and Transsacral Motor-Evoked Potentials: A Novel Test for Spino-Anorectal Neuropathy in Spinal Cord Injury

OBJECTIVES: Spinal cord injury (SCI) causes anorectal problems, whose pathophysiology remains poorly characterized. A comprehensive method of evaluating spino-anorectal function is lacking. The aim of this study was to investigate the neuropathophysiology of bowel dysfunction in SCI by evaluating motor-evoked potentials (MEP) of anus and rectum following transspinal magnetic stimulation and anorectal physiology. METHODS: Translumbar and transsacral magnetic stimulations, anorectal manometry, and pudendal nerve terminal motor latency (PNTML) were performed in 39 subjects with SCI and anorectal problems and in 14 healthy controls, and data were compared. MEPs were recorded with an anorectal probe containing bipolar ring electrodes. RESULTS: The MEPs were significantly prolonged (P < 0.05) bilaterally, and at lumbar and sacral levels, as well as at rectal and anal sites in SCI subjects compared with controls. A total of 95% of SCI subjects had abnormal MEPs and 53% had abnormal PNTML. All subjects with abnormal PNTML also demonstrated abnormal MEP, but 16/17 subjects with normal PNTML had abnormal MEP. Overall, SCI patients had weaker anal sphincters (P < 0.05), higher prevalence of dyssynergia (85%), and altered rectal sensation (82%). CONCLUSIONS: Translumbar and transsacral MEPs revealed significant and hitherto undetected lumbosacral neuropathy in 90% of SCI subjects. Test was safe and provided neuropathophysiological information that could explain bowel dysfunction in SCI subjects.