spinal nerve root stimulation · pspinal nerve root stimulation is a recently developed form of...

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EUROMODULATION is the therapeutic alteration of activity in pain pathways with the use of an im- plantable device. Although the process of neuro- modulation is not completely understood, it is thought to involve both inhibition and activation of relevant neural circuitry. In 1967, the first spinal cord stimulator was placed for the management of chronic pain. 36 Since then, SCS has been used for conditions such as radiculopathy, 11 FBSS, 29 peripheral neuropathy, 24 peripheral vascular dis- ease, 7 chronic unstable angina, 15 and complex regional pain syndrome. 23 For SCS, an electrical current is applied to the dorsal columns, creating a tingling sensation in the dermatomes whose afferent fibers traverse the regions being stimulat- ed. Through ill-defined mechanisms, this barrage of non- painful sensation attenuates the patient’s perception of pain; instead of feeling pain, the patient feels nonpainful paresthesias in the affected areas. 36 For stimulation to be effective, the area of paresthesia must overlap the area of pain. 30 Although in the initial SCS report 36 electrode place- ment in the subdural space was described, later investiga- tions revealed that the epidural space was a more optimal location. Although SCS has provided relief in a variety of painful conditions, it still has many limitations, including elec- trode migration, problems with electrode durability, and postural stimulation variability. 3 In addition, SCS provides incomplete and/or inconsistent coverage for areas such as the low back, buttock, feet, groin, pelvis, and neck. Be- cause the stimulator’s electrical current is limited in its ability to penetrate the spinal cord, stimulation is much less effective for pathways deep within the cord. Thus, some areas, such as those representing the S2–5 der- matomes, are almost completely out of reach. In recent years, with technological advancements and novel electrode placements along nondorsal column struc- tures, practitioners have begun to address some of these limitations. The use of PNS enables the application of stimulation to a particular peripheral nerve distribution. Occipital neuralgia, 39 trigeminal neuropathic pain, 37 and other painful neuralgias are examples of disorders am- enable to treatment with PNS. Of course, PNS has its lim- itations, including the need for surgical access to the tar- get nerve and restriction of pain relief to the distribution of the target nerve. Furthermore, peripheral nerve stimulators are often needed in regions of the body such as the neck or extremities that are highly mobile, placing high levels of stress along the course of the electrode systems. Spinal nerve root stimulation has emerged as another treatment option. Like PNS, this form of neurostimulation provides pain relief in areas inaccessible to SCS. Unlike PNS, however, spinal nerve root stimulators are located along the relatively stable and immobile spine. Numerous electrode placement strategies have been developed to accomplish spinal nerve root stimulation, including intraspinal, transforaminal, transspinal, and extraforami- nal nerve root stimulation. In this review we discuss the anatomy, techniques, advantages and disadvantages, and clinical studies available for each of these types of spinal nerve root stimulation. (See Table 1.) Intraspinal Nerve Root Stimulation Intraspinal nerve root stimulation uses an electrode located completely within the spinal canal, a placement in which the device preferentially stimulates the dorsal spinal rootlets (Fig. 1). In this fashion, stimulation pares- thesias can be focused solely within the receptive fields of these rootlets. Depending on the length of the electrode, one, two, or even several spinal segments may be targeted selectively. Neurosurg. Focus / Volume 21 / December, 2006 Neurosurg Focus 21 (6):E4, 2006 Spinal nerve root stimulation RAQEEB HAQUE, M.D., AND CHRISTOPHER J. WINFREE, M.D. Department of Neurological Surgery, Columbia University Medical Center, New York, New York Spinal nerve root stimulation is a recently developed form of neuromodulation used for the treatment of chronic pain conditions. Unlike spinal cord stimulation, in which electrical impulses are directed at the dorsal columns, spinal nerve root stimulation guides electrical current directly to one or more nerve roots. There are a variety of techniques by which this can be accomplished, yet no consistent terminology to describe these variations exists. In this review, the authors group the various techniques according to anatomical approach, define each category, describe and illustrate each of the techniques, review the available reports on their uses, and discuss the advantages and disadvantages of each one. KEY WORDS pain neuromodulation spinal nerve root stimulation intraspinal nerve root stimulation 1 Abbreviations used in this paper: FBSS = failed–back surgery syndrome; PNS = peripheral nerve stimulation; SCS = spinal cord stimulation. N Unauthenticated | Downloaded 06/13/20 03:11 PM UTC

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Page 1: Spinal nerve root stimulation · PSpinal nerve root stimulation is a recently developed form of neuromodulation used for the treatment of chronic pain conditions. Unlike spinal cord

EUROMODULATION is the therapeutic alteration ofactivity in pain pathways with the use of an im-plantable device. Although the process of neuro-

modulation is not completely understood, it is thought toinvolve both inhibition and activation of relevant neuralcircuitry. In 1967, the first spinal cord stimulator wasplaced for the management of chronic pain.36 Since then,SCS has been used for conditions such as radiculopathy,11

FBSS,29 peripheral neuropathy,24 peripheral vascular dis-ease,7 chronic unstable angina,15 and complex regionalpain syndrome.23

For SCS, an electrical current is applied to the dorsalcolumns, creating a tingling sensation in the dermatomeswhose afferent fibers traverse the regions being stimulat-ed. Through ill-defined mechanisms, this barrage of non-painful sensation attenuates the patient’s perception ofpain; instead of feeling pain, the patient feels nonpainfulparesthesias in the affected areas.36 For stimulation to beeffective, the area of paresthesia must overlap the area ofpain.30 Although in the initial SCS report36 electrode place-ment in the subdural space was described, later investiga-tions revealed that the epidural space was a more optimallocation.

Although SCS has provided relief in a variety of painfulconditions, it still has many limitations, including elec-trode migration, problems with electrode durability, andpostural stimulation variability.3 In addition, SCS providesincomplete and/or inconsistent coverage for areas such asthe low back, buttock, feet, groin, pelvis, and neck. Be-cause the stimulator’s electrical current is limited in itsability to penetrate the spinal cord, stimulation is muchless effective for pathways deep within the cord. Thus,some areas, such as those representing the S2–5 der-

matomes, are almost completely out of reach. In recent years, with technological advancements and

novel electrode placements along nondorsal column struc-tures, practitioners have begun to address some of theselimitations. The use of PNS enables the application ofstimulation to a particular peripheral nerve distribution.Occipital neuralgia,39 trigeminal neuropathic pain,37 andother painful neuralgias are examples of disorders am-enable to treatment with PNS. Of course, PNS has its lim-itations, including the need for surgical access to the tar-get nerve and restriction of pain relief to the distribution ofthe target nerve. Furthermore, peripheral nerve stimulatorsare often needed in regions of the body such as the neckor extremities that are highly mobile, placing high levelsof stress along the course of the electrode systems.

Spinal nerve root stimulation has emerged as anothertreatment option. Like PNS, this form of neurostimulationprovides pain relief in areas inaccessible to SCS. UnlikePNS, however, spinal nerve root stimulators are locatedalong the relatively stable and immobile spine. Numerouselectrode placement strategies have been developed toaccomplish spinal nerve root stimulation, includingintraspinal, transforaminal, transspinal, and extraforami-nal nerve root stimulation. In this review we discuss theanatomy, techniques, advantages and disadvantages, andclinical studies available for each of these types of spinalnerve root stimulation. (See Table 1.)

Intraspinal Nerve Root Stimulation

Intraspinal nerve root stimulation uses an electrodelocated completely within the spinal canal, a placement inwhich the device preferentially stimulates the dorsalspinal rootlets (Fig. 1). In this fashion, stimulation pares-thesias can be focused solely within the receptive fields ofthese rootlets. Depending on the length of the electrode,one, two, or even several spinal segments may be targetedselectively.

Neurosurg. Focus / Volume 21 / December, 2006

Neurosurg Focus 21 (6):E4, 2006

Spinal nerve root stimulation

RAQEEB HAQUE, M.D., AND CHRISTOPHER J. WINFREE, M.D.

Department of Neurological Surgery, Columbia University Medical Center, New York, New York

PSpinal nerve root stimulation is a recently developed form of neuromodulation used for the treatment of chronic painconditions. Unlike spinal cord stimulation, in which electrical impulses are directed at the dorsal columns, spinal nerveroot stimulation guides electrical current directly to one or more nerve roots. There are a variety of techniques by whichthis can be accomplished, yet no consistent terminology to describe these variations exists. In this review, the authorsgroup the various techniques according to anatomical approach, define each category, describe and illustrate each ofthe techniques, review the available reports on their uses, and discuss the advantages and disadvantages of each one.

KEY WORDS • pain • neuromodulation • spinal nerve root stimulation •intraspinal nerve root stimulation

1

Abbreviations used in this paper: FBSS = failed–back surgerysyndrome; PNS = peripheral nerve stimulation; SCS = spinal cordstimulation.

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Surgical Technique

For the percutaneous retrograde approach to target thelumbosacral nerve roots, the introducer needle is directedinto the epidural space at a lumbar level. Once placed, theelectrode is passed in a retrograde fashion (toward the sa-crum) and advanced to a location parallel to and overlyingthe lumbar and/or sacral nerve roots.6 In the originaldescription, the investigators stated that up to two adjacentsegmental nerve root distributions could be stimulated si-multaneously. Contraindications to this approach includeepidural fibrosis, spina bifida occulta, lateral and centralstenosis, spondylosis, and spondylolisthesis.3 For the per-cutaneous anterograde approach to target the lumbosacral

nerve roots, the introducer needle is directed through thesacral hiatus into the epidural space (Fig. 2). Once placed,the electrode is passed in an anterograde direction (towardthe head) and advanced to the appropriate location.17,18

Although these initial descriptions of spinal nerve rootstimulation were limited to the lumbosacral spine, thesame techniques may be used to place intraspinal nerveroot stimulators almost anywhere along the spinal axis.

Clinical Studies

In early reports of this technique, investigatorsdescribed anterograde electrode placement along lumbarnerve roots through a laminotomy to treat intractable low-back pain.8 In later investigations both anterograde6 andretrograde18 percutaneous electrode placement methodswere described. There are a number of indications for thecephalocaudal approach for nerve root stimulation; theseinclude pelvic pain4 and perineal pain of urological ori-gin,33 pelvic motor dysfunction,4 urinary urge inconti-nence,2,34 detrusor dysfunction,2 and interstitial cystitis.18

Before the advent of this technique, chronic pain manage-ment in the sacral dermatomes had primarily focused ontranssacral extraforaminal approaches to the nerve root(see later discussion). Because of the unique anatomy of

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2 Neurosurg. Focus / Volume 21 / December, 2006

FIG. 1. Anteroposterior radiograph showing an intraspinal nerveroot stimulator electrode placed on the right side of T-4. The elec-trode is located completely within the spinal canal, and stimulatesthe T3–5 dorsal spinal rootlets.

FIG. 2. Photograph of a lumbosacral spine model with cutawaysacral laminectomy used to demonstrate the technique for antero-grade placement of an intraspinal sacral nerve root stimulator elec-trode on the right side through the sacral hiatus.

TABLE 1Classification of spinal nerve root stimulation techniques

Technique

Category Intraspinal Transforaminal Extraforaminal Transspinal

indicated pelvic pain, perineal pain ilioinguinal neuralgia urinary urge incontinence described in pelvic motor dysfunction discogenic back pain urgency–frequency syndromes cadavers onlyurinary urge incontinence FBSS urinary retention, pelvic floor muscle overactivitydetrusor dysfunction interstitial cystitis Fowler syndrome, fecal incontinenceepididymoorchialgia, vulvo- interstitial cystitis, cervical stenosisdynia, bilat foot pain, FBSS

contra- epidural fibrosis, epidural fibrosis foraminal stenosis unknownindicated spina bifida occulta spina bifida occulta obese patient w/ small neck unknown

stenosis, spondylosis stenosis, spondylosisspondylolisthesis spondylolisthesis

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the sacral nerve roots, the latter approach inconsistentlyprovided paresthesia to the appropriate area.

Anterograde intraspinal nerve root stimulators placedvia the sacral hiatus have been used to treat the pelvic painsyndromes epididymoorchialgia and vulvodynia.18 Inanother report, investigators described the successful useof this technique to target more rostral lumbar and sacrallevels in a patient with bilateral foot pain.42 More rostralplacement of the intraspinal nerve root electrodes, at theL1–2 level, enabled a series of patients with axial low-back pain from FBSS to experience pain relief.41 Place-ment of the electrodes at the T3–4 level produced analge-sia for a patient with chest wall pain, although the exactelectrode placement technique was not reported.42

Last, the dorsal root ganglion is another theoretical tar-get for intraspinal nerve root stimulation.42 Whereas dor-sal column stimulation typically applies current to path-ways mediating touch, vibration, and proprioception(dorsal columns), stimulation of the dorsal root gangliontheoretically applies current to pathways mediating tem-perature (spinothalamic tract) as well, pathways that arenormally out of reach for SCS. Thus, deranged tempera-ture sensations characteristic of neuropathic pains can beattenuated by neurostimulation in this manner.42

Transforaminal Nerve Root Stimulation

Transforaminal nerve root stimulation uses an electrodeplaced within the neural foramen through the spinal canal(Fig. 3). In this fashion, electrical current is applied direct-ly to the nerve root, dorsal root ganglion, and spinal nerve

within the foramen itself. Thus, stimulation paresthesiascan be focused within the distribution of a single spinalsegment.

Surgical Technique

Anatomically, the procedure is initially similar to retro-grade intraspinal nerve root stimulation; the electrode isfirst placed into the spinal canal in an identical fashion.Subsequently, however, the electrode is steered out of thespinal canal into the neural foramen so that it lies adjacentto the intraforaminal structures.6,18 In this fashion, one ormore (with additional electrodes) thoracic, lumbar, and/orsacral foramina can be cannulated (Fig. 4).

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Spinal nerve root stimulation

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FIG. 3. Anteroposterior radiograph showing L-5 and S-1 trans-foraminal nerve root electrodes in position on the right side.

FIG. 4. Photograph of a lumbosacral spine model with cutawaysacral laminectomy used to demonstrate the technique for retro-grade placement of a transforaminal S-3 nerve root stimulator elec-trode on the right side. The electrode is initially inserted into thespinal canal, but is then steered into the appropriate neural fora-men.

FIG. 5. Photograph of a lumbosacral spine model used todemonstrate the technique for placement of an extraforaminal S-3nerve root stimulator electrode on the right side. The electrode isplaced from outside of the neural foramen directly into the foramenalong the nerve root’s course.

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Clinical Studies

The transforaminal technique has been described in anumber of reports.6,18 With such an approach, it has beenpossible to target thoracic, lumbar, and sacral nerve roots.Using the technique described earlier, patients with ilioin-guinal neuralgia, discogenic back pain, FBSS, and inter-stitial cystitis experienced alleviation of their symptoms.14

The exact pattern of electrodes used depends on the distri-bution of the patient’s pain and pattern of paresthesiasgenerated by the resultant electrical stimulation during theprocedure. In general, most patients with pelvic pain syn-dromes have a favorable response to bilateral S-2 and/orS-3 electrodes. Of course, a variety of electrode patternscan be used, and can include more caudal nerve roots aswell, depending on the needs of the patient.

Possible complications of the transforaminal approachare similar to those of the intraspinal approach, includingcerebrospinal fluid leakage and inappropriate placementof the stimulator in the intrathecal sac.18 In addition, be-cause the electrode must turn into the foramen, nerve rootdamage is also a concern.

Extraforaminal Nerve Root Stimulation

The extraforaminal technique for nerve root stimulationinvolves stimulating the nerve root from an “outside-in”approach. That is, the electrode is directed into the fora-men from outside the spine. In this manner, the electrodeis not introduced into the spinal canal prior to entering theneural foramen (Fig. 5).

Surgical Technique

The extraforaminal approach has historically been usedfor access to the sacral nerve roots and more recently, inone case report, to stimulate cervical nerve roots. Sacralnerve stimulation has been an important advancement inneuromodulation of urinary and pelvic dysfunction, andwill be discussed in detail in this section.

Early efforts at sacral nerve stimulation involved place-ment of an electrode into the S-3 foramen via a posteriorapproach after surgical exposure of the posterior aspect ofthe sacrum.38 Because the electrode is placed directly intothe foramen through the incision, no epidural access is ini-tially required. The two most notable limitations of this

technique are technical issues with regard to securing thetemporary lead, reliably locating the S-3 foramen, and theexcessive invasiveness of the procedure. Modificationssuch as the use of fluoroscopy to localize the S-3 foramen,the use of a much smaller incision, and the introduction ofmore secure leads have addressed many of the limitationsof this technique.12

There has been one report of cervical extraforaminalnerve root stimulation;16 this is the only published descrip-tion of cervical nerve root stimulation for pain relief.Patients in whom other methods of nerve root stimulationare contraindicated, such as those with scarring from pre-vious surgery or severe spondylosis, may be candidatesfor this technique. In preparation for the procedure, a su-pine patient’s cervical foramen is identified using fluo-roscopy. The introducer needle is then advanced in a tra-jectory parallel to the nerve root, into the posterolateralaspect of the foramen, avoiding the adjacent neurovascu-lar structures (Fig. 6). The electrode is placed through theneedle, which is then removed, leaving the stimulationelectrode posterior and parallel to the nerve root. Risks in-clude the following: pneumothorax; vertebral and carotidartery laceration; and spinal cord, accessory nerve, andcervical nerve root injury. Relative contraindications in-clude foraminal stenosis, which may increase the risk ofnerve root injury, and obese, short-necked stature, whichmay increase the risk of neurovascular injury.16

Clinical Studies

The first attempts at extraforaminal sacral nerve rootstimulation involved placement of the electrodes along theventral roots to improve bladder function.10 Patients withtetraplegia who suffered from bladder dysfunction werereported to have decreased residual volumes and reducedincidences of urinary tract infections after ventral rootstimulation. More recently, a large study25 showed thatboth sacral deafferentation and anterior root stimulationcould also ameliorate urinary dysfunction in paraplegicpatients. Although ventral nerve root stimulation is effec-tive for improving bladder function, it can be associatedwith cerebrospinal fluid leakage, sacral root injury, andpostoperative urinary tract infection.10,25

Dorsal sacral nerve root stimulation has also beenproven to be effective for urinary and other pelvic dys-

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4 Neurosurg. Focus / Volume 21 / December, 2006

FIG. 6. Photographs of cervical spine models used to demonstrate placement of an extraforaminal cervical nerve rootstimulator electrode on the right side. A: Anteroposterior view of the model, in which the electrode is placed from out-side of the neural foramen directly into the foramen along the posterolateral aspect of the nerve root. B: Lateral view ofthe model. Note the posterolateral positioning of the introducer needle to avoid the vertebral artery.

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functions, while maintaining a more acceptable side-effectprofile than ventral nerve root stimulation. Extraforaminalsacral nerve root stimulation has been used to treat urinaryurge incontinence,2,34 urgency–frequency syndromes,21

urinary retention,22 pelvic floor muscle overactivity,31

Fowler syndrome,21 fecal incontinence,21 and interstitialcystitis.9,22,32,33,34 In many chronic voiding dysfunctions,there is a discoordination of reflexes between the bladder,sphincter, and pelvic floor muscles.13 Urinary retentionsyndromes can be due to either detrusor contraction orbladder outlet obstruction, both of which are amenable toextraforaminal sacral nerve root stimulation. In a multi-center trial conducted in 177 patients with urinary reten-tion, extraforaminal nerve root stimulation resulted bothin symptomatic relief after 1 year and a reduction in thenumber of patients who needed to self-catheterize.22 Asimilar improvement in voiding function was describedafter sacral nerve root neuromodulation in patients withnonobstructive urinary retention.1,35

Other indications for extraforaminal sacral nerve rootneuromodulation are fecal incontinence and interstitialcystitis.31 Urgency fecal incontinence, which is defined asfecal loss at the first urge to defecate, responds to sacralnerve root electrical stimulation in patients with intactsphincters.19,20,26 Similarly, magnetic sacral nerve rootstimulation can also benefit patients with fecal inconti-nence.28 Interstitial cystitis, a clinical condition character-ized by urinary frequency, urgency, intermittent bladderdiscomfort, and chronic pelvic pain has recently beenshown to be responsive to extraforaminal sacral nerve rootstimulation.40 Women with intractable interstitial cystitiswho were treated with percutaneous sacral nerve rootstimulation experienced a decrease in frequency, nocturia,and mean bladder pressure.27 In more recent studies it wasfound that sacral nerve root stimulation was beneficial inboth chronic and refractory interstitial cystitis.14,40 Thus,extraforaminal sacral nerve root stimulation appears to bean appropriate alternative in patients with medicallyrefractory interstitial cystitis.

Finally, there has been only one report in the literaturedescribing extraforaminal stimulation of cervical nerveroots for the treatment of pain.16 The patient in this casepresented with a numbness and burning in his left armcaused by a herniated disc and central spinal stenosis. A

cervical fusion provided no relief, and an SCS lead couldnot be placed because of the stenosis. This patient attainedacceptable pain relief following placement of an extra-foraminal nerve root stimulator electrode.

Transspinal Nerve Root Stimulation

Transspinal nerve root stimulation involves placementof an electrode within the neural foramen from the con-tralateral side (Fig. 7). This approach has been describedin cadavers only and has not yet been reported in clinicaltrials.5 However, this technique offers theoretical anatom-ical advantages over other options for the placement ofcertain nerve root stimulator electrodes. For example, thetransspinal technique readily permits the placement ofelectrodes in the cervical or high thoracic neural foramina,a difficult if not impossible task with transforaminal tech-niques.

Surgical Technique

In the transspinal approach, the introducer needle entersthe skin in a paramedian fashion, contralateral to and atthe level of the target nerve root foramen. The needle isadvanced through the interlaminar space in a directionroughly parallel to the target nerve root, until the epiduralspace is encountered along the midline. The electrode isthen advanced laterally through the epidural space until itenters the desired neural foramen adjacent to the targetednerve root. The cervical and upper thoracic nerves exit thespinal canal in a fairly perpendicular fashion, which is ide-ally suited to the transspinal approach. Unfortunately, thelocation of the vertebral artery along the upper cervicalspine and the attendant risk of vascular injury precludesthe use of the transspinal approach above C-5.5

Conclusions

Spinal nerve root stimulation is an important addition tothe armamentarium of neurostimulation techniques. Itprovides the selectivity of PNS with the ease of placementand durability of SCS. In this report we have classified thedifferent forms of nerve root stimulation according tomethod of electrode placement, described the techniques,

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FIG. 7. Photographs of cervical spine models used to demonstrate placement of a transspinal cervical nerve root stim-ulator electrode on the right side. A: Anteroposterior view of the model, in which the electrode is placed from the spinalcanal directly into the foramen parallel to the nerve root. B: Lateral view of the model showing placement of atransspinal cervical nerve root stimulator electrode on the right side.

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and reviewed the available clinical studies. Future techno-logical and methodological advancements in neurostimu-lation should further enhance the ability of the pain spe-cialist to treat even more difficult and inaccessible chronicpain conditions effectively.

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36. Shealy CN, Mortimer JT, Reswick JB: Electrical inhibition ofpain by stimulation of the dorsal columns: preliminary clinicalreport. Anesth Analg 46:489–491, 1967

R. Haque and C. J. Winfree

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37. Slavin KV, Wess C: Trigeminal branch stimulation for in-tractable neuropathic pain: technical note. Neuromodulation8:7–13, 2005

38. Tanagho EA, Schmidt RA, Orvis BR: Neural stimulation forcontrol of voiding dysfunction: a preliminary report in 22 pa-tients with serious neuropathic voiding disorders. J Urol 142:340–345, 1989

39. Weiner, RL, Reed KL: Peripheral neurostimulation for controlof intractable occipital neuralgia. Neuromodulation 2:217–221, 1999

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41. Yearwood TL: Intraspinal nerve root stimulation for the treat-ment of axial lumbar spine pain in post laminotomy syndrome,in 7th Meeting of the International NeuromodulationSociety. Rome, Italy, June 10–13, 2005. International Neuro-modulation Society: San Francisco, CA, 2005

42. Yearwood TL: Neuropathic extremity pain and spinal cordstimulation. Pain Med 7 Suppl 1: S97–S102, 2006

Manuscript received September 25, 2006.Accepted in final form October 23, 2006.Address reprint requests to: Christopher J. Winfree, M.D., De-

partment of Neurological Surgery, 710 West 168th Street, 5th Floor,New York, New York 10032. email: [email protected].

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