After upper motor neuron SCI, bowel reflex centres within the sacral spinal cord may be released from descending inhibition, and may be influenced by somatic input (Frost et al. 1993). A number of studies have shown that electrical or magnetic stimulation of the somatic nervous system can bring about an alteration in visceral function in humans. For example, Riedy et al. (2000) showed that short periods of electrical stimulation with perianal electrodes resulted in an increase in anal pressures.
The sacral anterior root stimulator (SARS) employs electrodes implanted onto the second, third and fourth sacral anterior nerve roots to deliver short bursts of high voltage stimulation several times daily resulting in increased colonic activity, reduced constipation and sometimes defaecation during the stimulation.
A significant number of electrical or magnetic stimulation methods have been proposed and tested for their ability to improve bowel function in individuals with upper motor neuron SCI. These techniques are varied, from the relatively inexpensive and non-invasive abdominal muscle stimulation belt (Korsten et al. 2004) and percutaneous peripheral nerve stimulation (Mentes et al. 2007), to more complex and invasive techniques including implantation of epineural electrodes (Davis et al. 2001) and epidural or anterior sacral root electrodes (Kachourbos & Creasey 2000; Chia et al. 1996; Binnie et al. 1991; MacDonagh et al. 1990) for functional electrical stimulation. Magnetic stimulation techniques have also been also used; a magnetic field is generated in order to induce an electric field, which then generates sufficient current to stimulate the peripheral nerves (Lin et al. 2002).
Sun et al. (1995) investigated the role of spinal reflexes in anorectal function. Their subjects (C6-T12 traumatic SCI) underwent anorectal manometry and electromyography before and after having a sacral posterior rhizotomy performed by the same neurosurgeon. They found that all subjects lost conscious control of the external anal sphincter as well as responses to intra-abdominal pressure and rectal distention (EAS electromyographic activity, increase in anal pressure), demonstrating the significant role of spinal reflexes.
A review paper on low amplitude chronic electrical stimulation of the sacral plexus (Kenefick & Christiansen 2004), has been reported to reduce fecal incontinence and constipation in selected patients with incomplete SCI. Magnetic stimulation may produce similar results and is noninvasive. Morren et al. (2001) studied the effects of magnetic sacral root stimulation on anorectal pressure and volume in individuals with fecal incontinence and in patients with SCI. They found that magnetic sacral root stimulation produces an increase in anal and rectal pressure and a decrease in rectal volume in healthy subjects and patients with fecal incontinence or a spinal cord injury.
A variety of methods using electrical or magnetic stimulation devices have been tested to determine whether or not they can improve bowel management outcomes in individuals with SCI.
The use of functional magnetic stimulation decreased mean colonic transit time (Tsai et al. 2009; Lin et al. 2002; Lin et al. 2001), as did stimulation of the abdominal muscles (Hascakova-Bartova et al. 2008; Korsten et al. 2004). While preliminary results for posterior tibial nerve stimulation in individuals with SCI appear promising, it is important to note that the statistical significance of the improvements in clinical and physiological parameters were not reported and the study involved only two participants (Mentes et al. 2007).
In terms of implanted electrical stimulation systems, Binnie et al. (1991) found that an implanted Brindley (sacral anterior root) stimulator did not reduce oro-caecal time for individuals with SCI, however, subjects in the stimulator group did experience a significant increase in defecation compared to the control SCI group (Binnie et al. 1991).-
Subsequent studies using sacral anterior root stimulation yielded improvements in bowel function, including better spontaneous evacuation (Lombardie et al. 2011; Sievert et al. 2010; Chia et al. 1996), reduced bowel program times (Kachourbos & Creasey 2000, Vallès et al. 2009, Lombardi et al. 2009), elimination of autonomic dysreflexia related to bowel management (Kachourbos & Creasey 2000), elimination of manual help for defecation (Macdonagh et al. 1990). Both Holzer et al. (2007), and increased quality of life (Sievert et al. 2010; Lombardi et al. 2011; Lombardi et al. 2009; Holzer et al. 2007; Kachourbos & Creasey 2000). Jarrett et al. (2005) found reduced number of incontinence episodes through the use of sacral nerve stimulation, but conflicting evidence on the effects on resting and squeeze anal canal pressures (Lombardi et al, 2011; Holzer et al. 2007; Jarrett et al. 2005). Gstaltner et al. (2008) found that sacral nerve stimulation improved fecal continence, quality of life, and deliberate retention of faeces in their study among subjects with cauda equine syndrome. Finally, the Praxis FES system increased the frequency of defecation and decreased the time required for bowel evacuation in one subject (Johnston et al. 2005).
Worsøe et al.’s (2013) review of nerve stimulation techniques in neurogenic bowel dysfunction viewed neurostimulation as a way of ‘re-establishing neurogenic control and alleviating symptoms’.They reported that the sacral anterior root stimulator improves bowel function in some patients with complete SCI while sacral nerve stimulation can improve function in selected patients with a variety of incomplete neurologic lesions. They also suggest that peripheral stimulation using electrical stimulation or magnetic stimulation may offer non-invasive treatment alternatives for neurogenic bowels. However, they concluded that due to the lack of research evidence required to support informed choice, the latter techniques should be reserved for research at present.
There is level 1b evidence (from one RCT) (Korsten et al. 2004) that electrical stimulation of the abdominal wall muscles can improve bowel management for individuals with tetraplegia.
There is level 2 evidence (from one prospective controlled trial) (Binnie et al. 1991) that supports the use of sacral anterior root stimulation to reduce severe constipation in complete SCI.
There is level 4 evidence (from one pre-post study with two subjects) (Mentes et al. 2007) that posterior tibial nerve stimulation improves bowel management for those with incomplete SCI.
There is level 4 evidence (from one pre-post study with two subjects) (Johnston et al. 2005) that the Praxis FES system increases the frequency of defecation and decreases time required for bowel care in individuals with SCI.
Electrical stimulation of the abdominal wall muscles can improve bowel management for individuals with tetraplegia.
Functional magnetic stimulation may reduce colonic transit time in individuals with SCI.
Sacral anterior root stimulation reduces severe constipation in individuals with SCI.