[Pudendal nerve stimulation therapy of the overactive bladder -- an alternative to sacral neuromodulation?]

Future indications for sacral nerve stimulation

AIM

The aim of this article was to determine the effect of sacral nerve stimulation (SNS) on the treatment of faecal incontinence, constipation, irritable bowel syndrome, mixed urinary and bowel disorders, spinal injury and neurodegenerative disease, pain syndromes, and sexual dysfunction.

METHOD

A Medline search was performed including the keywords and/or MeSH headings of 'sacral nerve stimulation', 'neuromodulation', 'artificial pacemaker', 'faecal incontinence', 'constipation' and 'anal pain'. Further studies were identified by cross-referencing from relevant articles and by appraisal of recent peer-reviewed conference abstracts and proceedings.

RESULTS

SNS has been used for the treatment of urinary, bowel and sexual dysfunction, as well as pain resulting from such disorders, and dysfunction arising from nerve injury and degenerative disease. There is a paucity of high quality evidence to support the use of SNS for the majority of novel indications at present.

CONCLUSION

Good quality prospective, cross-over studies are required to determine the true benefits of SNS. Further research into patient selection, operative technique and stimulation parameters for existing indications will ensure a place for SNS in the future treatment algorithm of functional pelvic floor disorders.

[Results of sacral nerve modulation for treatment of overactive bladder]

Currently, sacral nerve modulation (SNM) is an effective treatment for overactive bladder symptoms which are refractory to anticholinergic or muscarinergic treatment. However, SNM requires the implantation of stimulation electrodes at the sacral nerves and a subcutaneous impulse generator. The SNM procedure can be divided into three phases: the acute phase comprising the implantation of the test stimulation electrodes, the subchronic stimulation phase over a period of 7-14 days during which neurostimulation takes place by means of an external impulse generator, and finally chronic SNM after implantation of the final impulse generator. In 1981 the SNM technique for treatment of bladder dysfunctions was first developed by Tanagho and Schmidt and has since been refined, while the range of indications has been extended continuously. It has been shown that patients with neurogenic bladder dysfunctions are able to gain the greatest benefit from SNM. The long-term results of SNM are very encouraging so far. In addition, a highly innovative and promising technique is the implantation of a miniaturized impulse generator with integrated stimulation electrode at the n. pudendus. However, the outcome of these trials has not fully been capable of living up to the expectations so far.

Sacral neuromodulation as a functional treatment of bladder overactivity

Sacral neuromodulation, namely the electrical stimulation of the sacral nerves has become an alternative treatment for cases of idiopathic bladder overactivity. The mechanism of action in this type of spinal cord modulation is only partially understood but it seems to involve stimulation of inhibitory interneurons. Temporary sacral nerve stimulation is the first step. It consists of the temporary application of neurostimulation as a diagnostic test in order to check the integrity of the sacral root and determine the best location for the implant. If the test stimulation is successful, a permanent device is implanted. In experienced hands, this is a safe procedure. When the patients are selected on the basis of sound criteria, more than three-quarters of them show a clinically significant improvement with a reduction in the frequency of incontinence episodes by more than 50%; however, the results vary according to each author's method of evaluation. The application of this technique should be combined with careful follow-up and attentive adjustments of the stimulation parameters in order to optimize the coordination of activity between the neurological systems involved.

Current opinion on the working mechanisms of neuromodulation in the treatment of lower urinary tract dysfunction

PURPOSE OF REVIEW

Neuromodulation is a successful treatment for patients with refractory lower urinary tract dysfunction. In the recent years, more applications of various types and ways have been developed and put into clinical practice. It is important, therefore, for urologists to know the existing theories on the working mechanisms that explain the effect. Although much research has been devoted to this subject for the past 35 years, the working mechanism is still unknown. This review presents an overview of the different theories and research into the physiological background of neuromodulation during the past 3 decades with emphasis on recent developments.

RECENT FINDINGS

Specific receptors in the spinal cord have been identified, which are involved in the working mechanism of neuromodulation. The maximal effect of neuromodulation is not directly reached, indicating that neuromodulation induces learning changes (i.e. neural plasticity). The carry-over effect could be caused by negative modulation of excitatory synapses in the central micturition reflex pathway.

SUMMARY

Neuromodulation in the treatment of stress incontinence probably induces physiological changes in the sphincter muscles and pelvic floor. In the treatment of overactive bladder syndrome, nonobstructive voiding dysfunction and chronic pelvic pain, the mechanism of action seems to be more complicated. Most likely, it is a combination of the different suggested modes of action, involving the neuroaxis at different levels.