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Pain


epidural and peripheral electrodes,25,52 pain and coccygodynia.54


and paddle electrodes;53 and pelvic


Lower back pain, being the most prevalent of the truncal pain syndromes, was a subject of a recent multicenter outcome study performed on a nationwide scale in Austria.55


In this study, the clinical outcomes of 111


patients with focal, non-cancer pain were retrospectively analyzed for at least three months after permanent implantation. Sixty-six of these 111 patients had either lower back pain or back pain with leg pain due to failed back surgery syndrome; the rest suffered from neck pain, post-herpetic neuralgia, thoracic back pain, tension headache, and facial pain. The overall improvement of pain was more than 50 % (reduction from 8.2 to 4.0 on a numerical rating scale of 0 to 10) for the entire group. In addition to this, the group of stimulated patients experienced sustained reduction in demand for analgesics.55


this study and a 24 % observed complication rate,55


Despite the retrospective nature of its results, along with


another study that investigated the efficacy of combined SCS and PNFS in the treatment of lower back and leg pain in a series of 20 consecutive patients,52


allowed Medtronic to receive the Conformité Européenne (CE) mark for its 16-electrode, fully implantable system for the percutaneous delivery of PNS for the management of chronic back pain in May 2011.


Not surprisingly, a major shift in indications for PNS coincided with the introduction of percutaneous insertion techniques, when treatment of craniofacial pain syndromes became amenable to PNS interventions. Prior to that, exposure of trigeminal branches56


and occipital nerves7,9,27


that provide sensory supply to the head and face region was technically challenging. But when placing an electrode became as simple as insertion of a guiding needle into the epifascial plane,10


many centers


started using percutaneous PNS for treatment of all kinds of neuropathic pain in the craniofacial region.57–61


With mostly anecdotal reports, various


indications, such as supraorbital neuralgia, infraorbital neuropathic pain, post-herpetic neuralgia in the ophthalmic nerve distribution, and occipital pain due to post-surgical neuroma, were explored. Based on this experience, larger series of patients were collected and presented. These included trigeminal neuropathic pain,62–64 treated with percutaneous65


and paddle-type electrodes,66–68 chronic cervicogenic headaches and migraines.29,66,69–72


The use of PNS for migraines that started with the publication of Popeney and Aló69


occipital neuralgia and, finally,


In addition to occipital PNS, migraines have been successfully treated with a combination of supraorbital and occipital electrodes76,77 more recently, with bilateral auriculotemporal nerve stimulation.78


and, The


rationale here is that stimulation appears to be most effective when applied to the area of maximal pain, and therefore some patients would benefit more from an individualized approach to PNS electrode insertion as the headache location in migraine sufferers tends to involve different parts of the head.


Less common, but perhaps even more resistant to treatment, and definitely more disabling overall, conditions treated with PNS are cluster headaches and hemicrania continua. Both of these pain categories were successfully treated with occipital nerve stimulation,79–84 supraorbital PNS,85


vagus nerve stimulation,86 sphenopalatine ganglion stimulation.87 and, more recently, with Here PNS may be a less invasive


alternative to the earlier-introduced hypothalamic DBS and perhaps serve as a first step in neuromodulatory treatment, leaving DBS as an option for PNS failures.


Finally, the latest, and perhaps most unexpected, PNS indication in the treatment of pain became diffuse pain of fibromyalgia.88,89


Here, in a


The results of this study revealed that nine of the 11 patients proceeded with permanent implantation and that at six-month follow-up there was an overall 45 % decrease in pain and a significant decrease in the amount of positive trigger points and the overall score on the fibromyalgia impact questionnaire, making the authors conclude that the results of the original prospective study had been confirmed in a placebo-controlled manner.90


Following this success in a prospective uncontrolled cohort, the same group of investigators implanted another 11 fibromyalgia patients and then stimulated them in a placebo-controlled cross-over fashion.90


first group of 12 patients satisfying the criteria for fibromyalgia, occipital PNS was implanted for control of occipital headache—and, in addition to improvement in headache severity, patients were found to have significant improvement in scores for bodily pain, depression, fatigue, and quality of life.88


immediately attracted the attention of both the implanting community and the device manufacturers, as the prevalence of migraines and percentage of medically intractable cases make this indication potentially larger than all other current indications together (with the exception of another potential PNS indication—lower back pain). Subsequently, all three large neuromodulation companies (Medtronic Neuromodulation, Minneapolis, MN; St Jude Neuromodulation, Plano, TX; and Boston Scientific Neuromodulation, Valencia, CA) started prospective controlled studies investigating the feasibility and efficacy of occipital nerve stimulation in the treatment of intractable migraines.73–75 The results of all three studies were positive overall and, in the end, PNS became approved for treatment of intractable migraines in Europe (at the time of writing, European CE Mark approval was received by St Jude Medical for its GenesisTM neurostimulation system for PNS of the occipital nerves for the management of the pain and disability associated with intractable chronic migraine).


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Technical Details and Complications The most attractive part of the PNS approach is its low invasiveness. Instead of putting electrodes into or over the patient’s brain, as in DBS or motor cortex stimulation, or into the spinal epidural space, as in SCS or nerve root stimulation, the entire electrode array is positioned in the vicinity of the stimulated peripheral nerve. In the case of PNFS, the electrode is placed subcutaneously in the region of maximal pain. Such an approach inevitably translates into increased safety—and, although there are many reports describing various complications that arise from the use of PNS and PNFS procedures,91–95


most of these complications are


minor and do not represent any threat to the life or neurological function of the patient operated on.


As a matter of fact, the most likely reason for the higher PNS complication rate is the lack of dedicated hardware, as PNS for treatment of chronic pain is mainly performed with devices developed and marketed for SCS applications.95


Nevertheless, it is worth mentioning that patients should be routinely informed that their PNS systems may malfunction, the hardware components may become broken or disconnected, they may erode through the skin and/or become infected, and electrodes may provoke


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