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Peripheral Nerve Stimulation for Neuropathic Pain


muscle spasms or migrate from their optimal location necessitating reprogramming or repositioning. It appears that some of these complications may be resolved without additional surgery, but even in those cases where surgery is needed to revise, replace, or remove an affected device, it can be safely done on an outpatient basis with minimal, if any, morbidity.


Most percutaneous electrodes used today have either four or eight cylindrical contacts placed along a single wire-like lead. In the future the number of contacts is expected to grow to 12 or even 16, thereby increasing the length of potential stimulation targets. These percutaneous electrodes may be implanted through a needle that is inserted under the skin in an epifascial plane. Paddle electrodes are larger and generally more stable; here, the flat metal contacts (four, eight or 16 per paddle) are positioned on a hard plastic backing that insulates the surrounding tissues. Among their benefits are a lower incidence of migration and the unidirectional nature of stimulation that aims electrical signals toward the stimulated nerve and away from adjacent sensitive tissues. These electrodes, however, usually require open surgical exposure of the nerve or stimulated area; they are also harder to remove if such removal is required in the future.


Similarly to the SCS procedure, PNS and PNFS start from careful patient selection and mandatory (in most practices) psychological evaluation. The final step before permanent device implantation is the stimulation trial when temporary electrodes are inserted and tested for efficacy and side effects. Such a trial usually lasts between three and seven days, although in some centers, particularly in European countries, it may last up to two months. During the trial period, patients determine the benefits of stimulation, helping them gauge expectations and determine whether permanent implantation is warranted. For the entire duration of the trial the patients remain connected to an external screening device that has most features of the stimulation that will be delivered by the implanted generator if the trial succeeds. At the end of this trial, temporary electrodes are removed (if the trial fails) or get replaced with permanent ones (if the trial was successful). Permanent PNS/PNFS electrodes are anchored in place and then tunneled toward an implantable pulse generator (IPG) that is usually placed at some distance


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away from the stimulated region. The IPG device may have a primary cell or be rechargeable—this rechargeability allows a reduction in device volume and an extension of its longevity, but usually comes at a slightly higher price and requires active participation/maintenance from the patient, who has to recharge the IPG on a regular basis. There are many devices and hardware combinations on the market today allowing implanters to come up with individualized sets of electrode leads and generators depending on pain location, stimulation requirements, patient characteristics, etc.95


Future Directions


It appears that PNS is today the most rapidly growing field of neuromodulation.96


With the recent regulatory approval of PNS in Europe for the treatment of chronic lower back pain and intractable migraines, it is expected that clinical interest in this modality will continue to rise. Among other things, this carries a hope that there will now be some much-needed objective evidence that determines the true efficacy of PNS and the best indications and most appropriate parameters of stimulation.


Associated research activity may also shed some light on the PNS mechanism of action which will then translate into further individualization of treatment and through it into optimization of immediate and long-term outcomes. Moreover, among important questions that remain open is the issue of the cost-effectiveness of PNS, as the high cost of implanted devices has to be justified in the view of ongoing efforts to contain healthcare costs.


As to progress in the PNS field itself, it appears that it will continue in all three directions—new indications, new targets and new devices—each of which deserves a separate article due to the unlimited opportunities that these directions represent. One of the main turning points in this process will be official endorsement of the entire approach through its regulatory approval, not only in Europe but worldwide, particularly in the US, which represents the biggest neuromodulation market today. Such endorsement will allow implanters to use approved devices for approved indications—instead of doing it on an ‘off-label’ basis—and at the same time will give device manufacturers a chance to market these devices and support education on their rational use. n


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15. Lipov EG, Joshi JR, Sanders S, Slavin KV, Use of peripheral subcutaneous field stimulation for the treatment of axial neck pain: a case report, Neuromodulation, 2009;12:292–5.


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23. Matharu M, Bartsch T, Ward N, et al., Central neuromodulation in chronic migraine patients with suboccipital stimulators: a PET study, Brain, 2004;127:220–30.


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