Latency of compound muscle action potentials of the anal sphincter after magnetic sacral stimulation

The aim of this study was to present the failure rate and normal values for motor latency of the anal sphincter after magnetic sacral stimulation (LMSS) using a modified recording technique. A bipolar sponge electrode was placed in the anal canal for recording. A ground electrode was placed in the rectum to reduce stimulus artifact. Magnetic stimulation was induced through a twin coil energized by a Maglite-r25 generator. Two groups were examined: 14 healthy volunteers and 14 patients with a spinal cord injury (SCI) above the conus. Nine of 56 studies (16%) failed. There were no significant differences in latency between right- and left-sided stimulation or between the healthy group and the SCI patients. As described, LMSS measurements are minimally invasive and have a low failure rate. They may be used to test the integrity of the distal motor pathway in patients with bladder or bowel dysfunction who may benefit from continuous electrical sacral root stimulation.