The use of evoked electromyographic responses in diagnosing lesions of the cauda equina.

An electrophysiologic technique to evaluate the anatomic integrity of the peripheral pathways to the bladder and sphincters is described. Evoked electromyographic responses of the anal sphincter are produced by stimulating the bladder wall and urethra. Impulses travel via the pelvic nerves and cauda equina to the conus medullaris, activating the pudendal nerve nucleus and resulting in contraction of the external anal sphincter. Lesions along this pathway produce either prolonged latencies and depressed responses or complete loss of response. Correlation of the results of this technique in 110 patients with clinical myelographic and operative findings indicates that the technique is a useful clinical tool.