Principles of Sacral Nerve Stimulation (SNS) for the Treatment of Bladder and Urethral Sphincter Dysfunctions

Objectives. Sacral nerve stimulation (SNS) (Medtronic, Inc., Minneapolis, MN) is an exciting new treatment for refractory voiding disorders including urinary incontinence, retention, and voiding dysfunction. It is known that both voiding and continence reflex mechanisms are organized in the sacral spinal cord and that pathologic conditions can alter the balance between these two opposing mechanisms. Methods. The background and surgical technique of SNS will be presented. This will be followed by a discussion of hypotheses on how SNS works. Results. The beneficial effects of SNS are most reasonably attributed to activation of somatic afferent axons in the sacral spinal roots. This evoked afferent activity in turn modulates sensory processing and micturition reflex pathways in the spinal cord. Hyperactive voiding can be suppressed by direct inhibition of bladder preganglionic neurons as well as inhibition of interneuroneal transmission in the afferent limb of the micturition reflex. On the other hand, voiding in patients with urinary retention can be facilitated by inhibition of reflex pathways to the urethral outlet (guarding reflexes). Conclusions. SNS, a nonablative, minimally invasive technique for urologists, holds great promise for a large number of patients who suffer debilitating and refractory urinary symptoms.