Detrusor muscle and sphincteric response to anorectal stimulation in spinal cord injury

Twelve patients with spinal cord injuries were studied to determine whether the anal sphincter could be used as an index of urethral sphincter activity and to determine the bladder and striated sphincter response to anal and rectal stimulation. Electromyogram (emg) needle electrodes were placed in the external urethral sphincter, external anal sphincter and levator ani. The output of a cystometer was simultaneously recorded on the printout so that the relationship of the striated muscle response to distension of the bladder could be observed. The response to inserting a finger into the external anal canal, external anal sphincter stretch and rectal balloon distension was also observed. The external urethral and anal sphincter activity was closely linked during bladder contraction and anorectal stimulation. The levator ani showed divergent activity. Stretch of the external anal sphincter caused an initial period of increased striated muscle activity, then in 10 of 12 patients abrupt and often marked inhibition of both sphincters and levator ani developed with continued stretch. Ongoing bladder contractions were inhibited and a decrease in bladder tone developed in 7 of 12. Stretch of the rectum produced results similar to those with anal stretch except that bladder facilitation was seen in 4 of 12 patients.