Spinal cord stimulation

Stojanovic and Abdi • Spinal Cord Stimulation Pain Physician, Volume 5, Number 2, pp 156-1662002, American Society of Interventional Pain Physicians®ISSN 1533-3159 Spinal Cord Stimulation
Milan P. Stojanovic, MD* and Salahadin Abdi, MD, PhD#
Spinal cord stimulation is the most common mode of radiculopathy, failed back surgery syndrome, complex re- neuromodulation used in managing chronic low back pain.
gional pain syndrome, peripheral vascular disease, and is- It is minimally invasive and reversible as opposed to nerve There is substantial scientific evidence on the efficacy of The basic scientific background of the initial spinal cord spinal cord stimulation for treatment of low back and lower stimulation trials was based on the gate control theory of extremity pain of neuropathic nature. Clinical studies re- Melzack and Wall. It has been demonstrated in multiple vealed a success rate of from 50% to 70% with spinal cord studies that dorsal horn neuronal activity caused by periph- stimulation, with decreased pain intensity scores, functional eral noxious stimuli could be inhibited by concomitant improvement and decreased medication usage.
stimulation of the dorsal columns. Various other mecha-nisms, which may play a significant role in the mechanism This review discusses multiple aspects of spinal cord stimu- of action of spinal cord stimulation, include the suppres- lation, including pathophysiology and mechanism of action, sive effect of spinal cord stimulation on tactile allodynia, rationale, indications, technique, clinical effectiveness, and increased dorsal horn inhibitory action of gamma- aminobutyric acid (GABA), prevention or abolition of pe-ripheral ischemia, and effects on human brain activity.
Keywords: Spinal cord stimulation, failed back surgery
syndrome, low back pain, percutaneous implantation, com-
Spinal cord stimulation is indicated in low back pain with Spinal cord stimulation for treatment of chronic low back
back surgery syndrome is the most common indication.
pain has recently gained popularity. As opposed to nerve The stimulating electrodes are placed in the epidural space ablation, spinal cord stimulation is minimally invasive and either percutaneously or surgically depending on the se- reversible. The recent improvements in hardware design verity of the accessibility of the epidural space. Conse- have made implantation techniques simpler and resulted quently, the electrodes stimulate dorsal columns of the spi- in prolonged equipment longevity. Spinal cord stimula- nal cord; and, thus, the alternative term for spinal cord tion screening trial, which is performed before permanent stimulation is dorsal column stimulation.
implantation, is a relatively minor invasive procedure,which allows patients to test its effects before final im- The current trend among interventional pain practitioners plantation. The scientific evidence has shown better out- is to try spinal cord stimulation earlier in the course of comes with spinal cord stimulation in comparison to other chronic low back pain, even though for many years it was modalities for treatment of some forms of low back pain.
considered as a last option “when everything else failed.”However, considering the relatively low cost of spinal cord Spinal cord stimulation is by far the most common mode stimulation trials, its low risk-benefit ratio and favorable of neuromodulation used in chronic low back pain. Failed outcome studies, spinal cord stimulation may be the besttreatment option in some forms of chronic low back pain, From the Interventional Pain Program, MGH Pain Center, such as failed back surgery syndrome.
Department of Anesthesia and Critical Care, Massachu-setts General Hospital, and Harvard Medical School. *Dr.
Although its mechanisms of action have been attributed to Stojanovic is the director of interventional pain program.
Melzak and Wall’s (1) “gate control theory,” recent research #Dr. Abdi is the director of fellowship program. Address efforts have revealed new potential mechanisms of action.
correspondence: Milan Stojanovic, MD, Massachusetts It seems that spinal cord stimulation can at least partially General Hospital, 655 Concord Ave. #305, Cambridge, MA exert its actions through modulation of neurotransmitters Pain Physician Vol. 5, No. 2, 2002
Stojanovic and Abdi • Spinal Cord Stimulation mal model, while GABA antagonists abolished the anti-allodynic effect of spinal cord stimulation. In humans, the Humans opened an era of spinal cord stimulation by utiliz- intrathecal baclofen infusion produced significant augmen- ing the electrical power of torpedo fish in 600 BC. The tation of spinal cord stimulation effects (11). However, first attempts at brain electrical stimulation were reported further studies are needed to clarify the beneficial effects in 1874. However, the first implantation of brain elec- of concomitant use of spinal cord stimulation and intrath- trodes was not performed until 1948, for treatment of psy- ecal GABA agonists for the treatment of certain forms of chiatric disorder. Many attempts to use electrical CNS stimulation for treatment of pain emerged in the 1950s and1960s based on the gate control theory of pain proposed Other putative mechanisms may also be responsible for by Melzack and Wall in 1965 (1). Two years later, Shealy pain relief induced by spinal cord stimulation. Recent ani- and associates introduced spinal cord stimulation (2). Ini- mal and human studies revealed a potential role of adenos- tial spinal cord stimulation procedures involved open in- ine in mechanisms of action of spinal cord stimulation.
trathecal implantation of electrodes via laminotomy. The Intrathecal administration of adenosine receptor agonist lack of adequate hardware and paucity of clinical outcome was found to have a potentiating effect with spinal cord studies significantly slowed the development of stimulation and also a synergistic effect with baclofen (4).
Furthermore, the disinhibition of descending analgesiapathways originating in periaqueductal gray and/or the re- The hardware technology has substantially improved over lease of serotonin and substance P might explain the mecha- the years. Moreover, electrodes have become smaller in nism of action of spinal cord stimulation (12, 13).
shape and easier to navigate through the epidural space;and, finally, internal pulse generators have new program- Spinal cord stimulation may also abolish peripheral is- ming capabilities and a longer battery life span. All these chemic pain by rebalancing the ratio of oxygen supply and technological developments led to the successful applica- demand and thus preventing ischemia (5). At low levels tion of minimally invasive percutaneous stimulation trials of stimulation, spinal cord stimulation may act by suppress- for a variety of patients with low back pain.
ing the sympathetic activity via á-adrenoreceptors. How-ever, at increased levels of stimulation, the nitric oxide- MECHANISM OF ACTION
dependent release of calcitonin gene-related peptide mayplay a significant role in inducing vasodilatation (14). This The basic scientific background of the initial spinal cord might also explain the better survival of skin flaps during stimulation trials was the gate control theory by Melzack spinal cord stimulation (15). On the contrary, Kemler et al and Wall (1). Their theory proposed that stimulation of A- (16) reported that the use of spinal cord stimulation was beta fibers modulates the dorsal horn “gate” and therefore not associated with increase in peripheral blood flow.
reduces the nociceptive input from the periphery. Indeed,several studies demonstrated that dorsal horn neuronal Patients with chest pain due to refractory angina pectoris activity caused by peripheral noxious stimuli could be in- respond well to spinal cord stimulation. Many possible hibited by concomitant stimulation of the dorsal columns explanations exist for spinal cord stimulation’s mechanism (3). However, it seems that other mechanisms may play a of action in myocardial ischemia. The most likely mecha- more significant role in mechanisms of spinal cord nism for pain relief consists of redistribution of the coro- nary blood flow from regions with normal perfusion in fa-vor of regions with impaired myocardial perfusion (17).
Many animal studies showed a suppressive effect of spinal This anti-ischemic effect of spinal cord stimulation was cord stimulation on tactile allodynia, which is mediated shown by coronary blood flow measurements and positron via Aâ fibers and represents the state of central hyperex- emission tomography. Other lines of evidence show that citability (6, 7). Since allodynic animals seem to have lower modulation of the intrinsic cardiac nervous system might extracellular levels of gamma–amino butyric acid (GABA), contribute to the therapeutic effects of spinal cord stimula- one of the proposed mechanisms of spinal cord stimula- tion in patients with angina pectoris (18). In this proposed tion action involves increased dorsal horn inhibitory ac- mechanism, spinal cord stimulation may suppress the ex- tion of GABA (8-10). In those studies, intrathecal admin- citatory effects of myocardial ischemia on intrinsic car- istration of the GABA agonist baclofen enhanced the antinociceptive action of spinal cord stimulation in an ani- Pain Physician Vol. 5, No. 2, 2002
Stojanovic and Abdi • Spinal Cord Stimulation The effects of spinal cord stimulation on human brain ac- with paresthesia perception from spinal cord stimulation tivity were studied utilizing functional magnetic resonance coverage (20). They concluded that thickness of the dor- imaging (MRI). The spinal cord stimulation produced in- sal CSF layer is the main factor determining the percep- creased activity in the human somatosensory cortex (SI tion threshold and paresthesia coverage in spinal cord and SII areas), contralateral to the side of pain and cingu- stimulation. In other words, an increasing thickness raises late gyri. The somatosensory cortex activation becomes the threshold and reduces the coverage and vice versa. In more pronounced with increased spinal cord stimulation the same study, the effects of an asymmetrical electrode activity (19). These brain areas activated by spinal cord position with respect to the spinal cord midline were also stimulation correspond to CNS pain pathways involved in analyzed by computer modeling. The authors concluded processing of somatosensory (SI, SII) and affective com- that a lateral asymmetry of less than 1 mm gives a signifi- ponents (cingulate gyri) of pain. Further research may cant reduction of perception threshold and may result in better define the role of higher CNS structures during spi- unilateral spinal cord stimulation coverage.
The same group of investigators using MRI found that spi- ANATOMY AND HARDWARE
nal cord midline and vertebral midline are apart by at least1 to 2 mm in all levels investigated in 40% of patients.
For chronic low back/low extremity pain treatment, the Further, Bartolat et al found that only 27% of paresthesia spinal cord stimulation electrode leads are generally placed was felt symmetrically when the stimulating contacts were in the thoracic epidural space, with a lead tip location at perfectly located at the radiological midline (21). Conse- the T8-10 level. An electrical field from the leads reaches quently, adequate symmetrical spinal cord stimulation cov- the dorsal column of the spinal cord and modulates its pain erage of the low back and lower extremity is in many cases transmission. The anatomical position of the spinal cord stimulation lead is critical for “coverage” and, subsequently,pain relief. Holsheimer et al measured the dorsal CSF layer The permanent spinal cord stimulation hardware consists thickness in thoracic areas corresponding to spinal cord of a spinal cord stimulation lead, an extension cable, a stimulation electrodes’ placement and correlated results power source, and a pulse generator (Figs. 1 and 2). Many Fig. 1. Spinal cord stimulation lead, an exten- Fig. 2. Spinal cord stimulation lead, an exten- sion cable, a power source/ pulse generator and sion cable, a power source/ pulse generator sur- Pain Physician Vol. 5, No. 2, 2002
Stojanovic and Abdi • Spinal Cord Stimulation leads contain a removable stylet, which eases lead steer- ies have confirmed good outcomes of spinal cord stimula- ing during implantation. The lead design varies in the tion for low back pain and highlighted its advantages over number of electrodes from four to eight. The distance between the electrodes and the length of the leads alsocan differ. It is not clear if an increased number of elec- INDICATIONS
trodes provides better coverage, but it might be beneficialin case of lead migration. The leads with minimal space Axial vs. Radicular Pain
between electrodes (such as the Medtronic Quad com-pact lead) might be better suited for isolated axial low back Generally, patients with radicular pain to the lower ex- pain without a radiating component to the lower extremity.
tremities seem to respond better to spinal cord stimula- There are two types of pulse generators: (a) the com- tion than patients with isolated axial low back pain (22- pletely internal pulse generator containing a battery; and 41). However, a few studies have shown that axial low (b) an internal pulse generator supplied by external power back pain in combination with bilateral leg pain also re- through the radiofrequency antenna applied to the skin.
sponds well to spinal cord stimulation (27, 35, 42).
The implanted pulse generator is more convenient to useand can be easily adjusted by the patient using a small Low Back Pain and Lumbar Radiculopathy
telemetry device. Patients can turn the stimulator on andoff, and control the stimulation amplitude, frequency and Surgically naive patients who are poor candidates for sur- pulse width. A separate external programmer allows for gery may respond well to spinal cord stimulation. The more complex internal pulse generator reprogramming by chronic radicular pain in these patients is commonly of the physician. In case of inadequate stimulation, the phy- neuropathic origin. In these patients, it is important to sician can change polarity and number of functioning elec- rule out other sources of pathology, eg, facet disease, sac- trodes in order to provide better stimulation coverage. The roiliac arthropathy, internal disc disruption, piriformis syn- batteries have to be changed every 3 to 6 years, which drome, and/or myofascial pain, before choosing spinal cord requires a brief visit to the operating room. The battery life stimulation. In some cases of lumbar radiculopathy, bet- depends on the time the stimulator is used and the stimula- ter outcomes might be achieved by placing the spinal cord tion amplitude. The externally powered internal pulse gen- stimulation lead directly through the neural foramina (ret- erator has an advantage over the implanted one in patients requiring higher amplitudes of stimulation, which wouldotherwise deplete the implanted batteries in a short period Failed Back Surgery Syndrome
Failed back surgery syndrome is the most common indi- The permanent spinal cord stimulation implant can be cation for spinal cord stimulation placement in the United achieved by placing the percutaneous lead via epidural States today (37). It is defined as persistent pain after needle or “paddle’ lead via open laminotomy. The con- attempted surgical treatment for low back pain. Failed figuration of spinal cord stimulation electrodes varies in back surgery syndrome occurs in 20% to 40% of the more these two techniques. Percutaneous electrodes are the same than 200,000 American patients who undergo lumbar spine configuration as the ones used for the stimulation trial.
surgery each year (23). For patients who fail medical man- Paddle electrodes are larger and can be anchored directly agement, physical therapy and nerve blocks, spinal cord to the dura, potentially minimizing migration.
stimulation may be the treatment of choice. Many studiesare supporting the role of spinal cord stimulation in these RATIONALE
patients, emphasizing its advantages over re-operation(26).
Spinal cord stimulation is not a neurodestructive proce-dure as opposed to neuroablation. Its effects are easily re- Other Indications
versible. The relatively low invasiveness of a spinal cordstimulation trial (comparable to an epidural catheter place- Spinal cord stimulation has been shown to be beneficial ment), makes spinal cord stimulation the treatment of in many other chronic pain conditions. The literature sup- choice for certain forms of low back pain. In the long ports the use of spinal cord stimulation in complex re- term, this treatment modality can be more cost effective gional pain syndrome, peripheral vascular disease, and than conservative treatment options (Table 1). Many stud- ischemic heart disease (43, 44, 45). The use of spinal Pain Physician Vol. 5, No. 2, 2002
Stojanovic and Abdi • Spinal Cord Stimulation Table 1. Five-year medical costs of spinal cord stimulation
* Present values are calculated assuming a 5% real discount rate, published in 1997 SCS – spinal cord stimulationAdapted and modified from Bell et al (36).
cord stimulation in postherpetic neuralgia, diabetic neur-opathy, deafferentation pain and spinal cord injury pain is TECHNIQUE
Implantation Technique
Contraindications
The patient is placed in prone position, with a pillow un- Severe psychiatric diseases present major contraindications der the abdomen, to facilitate approach to the epidural for spinal cord stimulation implantation and psychologi- space. Both trial and permanent implantation are performed cal evaluation of the candidate patient is recommended under local anesthesia with light intravenous (IV) sedation before implantation. Infection, drug abuse and as needed. Most common entry sites for the lumbar area coagulopathies are also contraindications for spinal cord are the T12/L1 or L1/2 spinal interspaces. Anteroposte- stimulation placement. One should use caution in spinal rior fluoroscopic images are obtained, making sure that cord stimulation placement in patients with thoracic spinal the spinous processes are placed midline to the pedicles.
canal stenosis. This applies in particular to dual-lead sys- The needle entry site is just lateral to the spinous process.
The epidural space is identified by the loss-of-resistance Pain Physician Vol. 5, No. 2, 2002
Stojanovic and Abdi • Spinal Cord Stimulation technique. It is recommended that the lateral fluoroscopic successful trial include at least a 50% pain intensity reduc- views be checked during needle insertion, in order to as- tion, a decrease in analgesic intake and a significant func- sess needle depth. The spinal cord stimulation lead is in- serted in the epidural space under continuous fluoroscopicguidance. The curved lead tip can facilitate the desired lead There is no consensus on technical approach and the length positioning and treading. The goal is to position the lead of a spinal cord stimulation trial. Minimal trial time should midline to the spinous process fluoroscopic image or to its be 24 hours, although many centers perform 3- to 5-day lateral margin if unilateral coverage is intended. Further, trials. The initial inpatient trial allows for proper spinal lateral positioning of the spinal cord stimulation lead can cord stimulation adjustment, after which the patient is dis- cause lead dislodgment to the lateral or anterior epidural charged home for several days of “home” trial. In cases of space and, therefore, inadequate coverage. Once adequate equivocal results, the trial time can be extended.
lead position is obtained, trial stimulation is performed. Itis important that stimulation paresthesias provide at least There are two technical approaches for spinal cord 70% to 80% overlap with the patient’s pain location.
Permanent stimulator placement technique is similar to the ♦ Percutaneous Placement; Once the trial is completed, trial. While the trial is usually done in the pain clinic set- the lead is removed, and a new lead and internal pulse ting, permanent spinal cord stimulation placement is re- generator are placed (on separate occasions).
served for the operating room. Under local anesthesia and ♦ Open Surgical Approach; The second approach is to IV sedation, a skin incision is made along the lumbar in- tunnel and anchor the trial lead via surgical incision sertion site where the stimulator lead is placed and anchored and to later internalize it for permanent spinal cord to the skin. A separate subcutaneous pocket for a pulse stimulation placement. This approach simplifies the generator is made in the gluteal or abdominal area. The final procedure and assures that stimulation coverage spinal cord stimulation lead is then connected with the in- remains the same during both the trial period and per- ternal pulse generator by an extension cable tunneled un- manent implantation. Its major disadvantage is the der the skin. Finally, the skin and subcutaneous tissues are need for a second visit to the operating room for lead removal in case of an unsuccessful trial. The advan-tage of a percutaneous trial is its minimal invasive- Patients should avoid extreme activity for the first 6 to 8 ness with a similar low risk of complications as in rou- weeks following permanent spinal cord stimulation implan- tation in order to prevent lead migration and allow for epi-dural scar tissue formation.
The percutaneous trial followed by lead placement via lami-nectomy is another less frequently utilized approach for During trial and permanent lead implantation, care should spinal cord stimulation placement. In this case, a lead with be taken to obtain the best possible pain coverage (“sweet wider electrodes is placed via laminotomy during perma- spot placement”). The spinal cord stimulation topographic nent implantation. Wider electrodes might provide better coverage depends on the spinal level where the spinal cord coverage in certain patients and are less prone to migra- stimulation lead tip is positioned. For low back pain and tion in comparison to standard spinal cord stimulation leads lower extremity pain, the T9-10 levels are recommended; however, there is high intersubject variations in these guide-lines.
CLINICAL EFFECTIVENESS
Stimulation Trial
There is substantial scientific evidence on the efficacy ofspinal cord stimulation for treatment of low back and lower A stimulation trial is warranted before proceeding with extremity pain of neuropathic nature. Clinical studies have permanent spinal cord stimulation implantation. The per- revealed success rates of from 50% to 70% with certain cutaneous spinal cord stimulation trial is a minimally in- methods of spinal cord stimulation (22, 23, 24, 25). These vasive procedure and can positively predict a long-term studies have shown decreased pain intensity scores, func- outcome in 50% to 70% of cases. The trial allows the tional improvement and decreased medication use with patients to evaluate the spinal cord stimulation analgesic spinal cord stimulation treatment. The main drawback of activity in their normal surroundings. The criteria for a neurostimulation is a decrease in its effectiveness over time, Pain Physician Vol. 5, No. 2, 2002
Stojanovic and Abdi • Spinal Cord Stimulation seen in 20% to 40% of patients. It seems that this “toler- medical regimens and physical therapy, spinal cord stimu- ance’ to treatment is due to reorganization of the CNS (CNS lation may appear costly. However, the overall cost can plasticity) that takes place in neuropathic pain states. An- actually be lower than conservative management costs over ecdotal evidence suggests that not using the spinal cord time. If taken together, the cost of medications, emergency stimulation continuously, eg, shutting it off overnight, may room visits, multiple physician visits, X-rays, and absence decrease the development of tolerance.
from work can easily surpass the cost of spinal cord stimu-lation implant. Bell et al have shown that for those pa- It has been documented that patients with failed back sur- tients for whom spinal cord stimulation is clinically effica- gery syndrome respond better to spinal cord stimulation cious, spinal cord stimulation pays for itself within 2.1 years than the re-operation (26). Reported success rates in treat- ing failed back surgery syndrome vary from 12% to 88%,with higher efficacy reported in recent studies (27, 28, 29).
COMPLICATIONS
A systematic review of the literature related to spinal cordstimulation and failed back surgery syndrome by Turner et The spinal cord stimulation complications can be divided al (30) revealed that on average, 59% of patients had > 50% into surgical complications and hardware complications.
pain relief. The average complication rate in the same study The most common surgical complication is infection.
was 42% but related to mainly minor complications (Table Wound hematoma and seroma are other commonly encoun- 2). Besides pain relief, spinal cord stimulation improves tered surgical complications. Turner et al (30) performed functional status in a significant number of patients, with a a meta-analysis of spinal cord stimulation for failed back 25% return-to-work rate (27) and up to 61% improvement in surgery syndrome publications and found reported a 5% activities of daily living (31). The reduced consumption of incidence of infection and 9% incidence of other surgical analgesics with spinal cord stimulation treatment varies from complications. The authors also report that hardware com- 40% to 84% in published reports (24, 32).
plications include: lead migration (24%), lead failure (7%)and pulse generator failure (2%). While this analysis evalu- Certain psychological tests have been shown to predict ated studies using old hardware systems, it seems that the outcomes in spinal cord stimulation treatment (33). Al- rate of these complications is much lower currently. In though spinal cord stimulation is an excellent treatment our institution, we see much lower complication rates with choice for patients with failed back surgery syndrome (34, 35), more studies are needed to further narrow down thepatient selection criteria and improve long-term success Surgical Complications
Bleeding at the internal pulse generator site (subcutaneous OUTCOMES AND COST EFFECTIVENESS
hematoma) is usually self-limiting and gradually reabsorbsin a few weeks. Frequent exam of the hematoma site is Compared with the more conservative treatments, such as important, since hematoma can lead to infection.
Table 2. Complications and hardware failure in spinal cord stimulation
Adapted and modified from Bell et al (36).
Pain Physician Vol. 5, No. 2, 2002
Stojanovic and Abdi • Spinal Cord Stimulation Antibiotic prophylaxis regimens for spinal cord stimula- pain or only for axial low back pain combined with lower tion vary. The minimal prophylaxis should consist of pre- extremity pain. If the goal of spinal cord stimulation is to operative antibiotic coverage, eg, cefazolin 1 g IV. How- cover low back pain and bilateral lower extremities pain, ever, at many institutions, prophylactic antibiotics are given single- or dual-lead systems should be considered. Utiliz- up to 10 days postimplantation. Obtaining a CBC with ing a dual-lead system can potentially provide “deeper” differential urine analysis and sedimentation rate can fur- electrical field penetration in the dorsal column and there- ther decrease the risk of infection by excluding patients fore provide better axial low back pain coverage (42, 46).
who have any laboratory sign of infection. Usual signs of On the other hand, North et al (47) have shown that there post procedural infection are increased temperature and is no advantage in using the dual over single lead for axial tenderness at the incision site. Redness, swelling, and dis- low back pain and that a failure rate is higher in dual elec- charge at the insertion site can also occur. If infection oc- curs at the internal pulse generator insertion site, one shouldmake sure to first aspirate the site for cultures before initi- Four vs. Eight Electrode System
ating antibiotic coverage and removing the hardware.
Both four and eight electrodes were shown to be effective Inadequate Coverage or Spinal Cord Stimulation Mal-
in treatment of low back and lower extremity pain, with no function
apparent advantages of one system over the other. Eventhough it seems that eight electrodes may have the poten- In case of spinal cord stimulation malfunction, one should tial advantage in case of lead migration, this has yet to be obtain AP and lateral fluoroscopic images of the spinal cord stimulation lead tip, internal pulse generator and allconnections to rule out lead migration, breakage or dis- Internal vs. External Power Source
connection. If the cause is not found by fluoroscopy, oneshould analyze the internal pulse generator using the pro- An internalized, fully implanted power source offers ap- grammer. The battery status and impedance of each elec- parent advantages. It is more convenient for the patient to trode in relation to the internal pulse generator should be use, it is aesthetically more appealing, and it does not re- checked. If two electrodes have exactly the same imped- quire frequent external battery changes. However, in cer- ance, there might be a short circuit between them, most tain situations, the external power source can be indicated.
commonly located at the connector or internal pulse gen- This applies to all cases where high amplitudes of stimula- erator site. Some mechanical failures might require surgi- tion are needed during the trial phase. In particular, the cal revision and replacement of affected spinal cord stimu- required stimulation amplitude should be monitored when dual-lead systems are used. Dual-lead systems tend toempty batteries faster than one lead system even at modest Decrease in Stimulation Amplitude
stimulation amplitudes; and if an internal power source isused in such cases, these patients may require frequent The decreased stimulation threshold can be caused by in- trathecal migration of the spinal cord stimulation lead. Ifmigration stays unnoticed, it can lead to serious complica- Percutaneous vs. Laminectomy Approach
tions such as spinal cord injury. This complication seemsto be most common in patients with significant spinal ca- Percutaneous placement of the spinal cord stimulation lead nal stenosis. If intrathecal migration is suspected, the MRI is a less invasive procedure, minimizing immediate com- of targeted spinal level should be obtained before antici- plications and requiring less operating room time. Since pated spinal cord stimulation placement.
percutaneous electrodes are placed under monitored anes-thesia care, adequate spinal cord stimulation coverage can CONTROVERSIES
be confirmed during the permanent implantation, makingit a significant advantage over laminectomy style elec- Single- vs. Dual-Lead System
trodes, which are generally placed under general anesthe-sia, eliminating the patient’s feedback on stimulation cov- Adequate relief of axial low back pain using spinal cord stimulation remains a challenge. It is not clear if spinalcord stimulation is indicated for isolated axial low back On the contrary, laminectomy electrodes provide several Pain Physician Vol. 5, No. 2, 2002
Stojanovic and Abdi • Spinal Cord Stimulation advantages over percutaneous placed ones (48): Linderoth B, Foreman R. Physiology of spinal cord stimulation: Review and update. Neuromodulation They are anchored to the dura with minimal chance of Yakhnitsa V, Linderoth B, Meyerson BA. Spinal cord ♦ They are in closer contact with epidural space, and stimulation attenuates dorsal horn neuronal hyperex- they do not cause unnecessary posterior epidural space citability in a rat model of mononeuropathy. Pain Bennett G. An animal model of neuropathic pain: A CARDIAC PACEMAKERS AND SPINAL CORD
review. Muscle Nerve 1993; 16:1040-1048.
STIMULATION
Stiller CO, Cui CG, O’Connor WT et al. Release ofGABA in the dorsal horn and suppression of tactileallodynia by spinal cord stimulation in The interference and inhibition of the cardiac pacemaker mononeuropathic rats. Neurosurg 1996; 39:367-375.
can be caused by spinal cord stimulation. However, spinal Cui JG, O’Connor WT, Ungerstedt U et al. Spinal cord stimulation can be used in a patient with a pre-exist- cord stimulation attenuates dorsal horn release of ex- ing pacemaker if certain precautions are taken: citatory amino acids in mononeuropathy via aGABAergic mechanism. Pain 1997; 73:87-95.
♦ Both devices should be programmed in bipolar mode; 10.
Cui JG, Linderoth B, Meyerson BA. Effects of spinal ♦ The spinal cord stimulation frequency should be set cord stimulation on touch evoked allodynia involveGABAergic mechanisms. An experimental study in mononeuropathic rat. Pain 1996; 66: 287-295.
Each spinal cord stimulation programming should be Meyerson BA, Cui JG, Yakhnitsa V et al. Modulation performed using continuous ECG monitoring. More of spinal pain mechanisms by spinal cord stimulation importantly, the manufacturer’s recommendations and the potential role of adjuvant pharmacotherapy.
should be strictly followed, and the input of a cardi- Stereotact Funct Neurosurg 1997; 68:129-140.
Stiller CO, Linderoth B, O’Conner W et al. Repeatedspinal cord stimulation decreases the extracellular level CONCLUSION
of gamma-aminobutyric acid in periaqueductal greymatter of freely moving rate. Brain Res 1995; 669:231-241.
Spinal cord stimulation is an excellent treatment modality Linderoth B, Gazelius B, Franck J et al. Dorsal col- for carefully selected patients with low back and lower umn stimulation induces release of serotonin and sub- extremity pain. It may be a treatment of choice for pa- stance P in the cat dorsal horn. Neurosurg 1992; tients with failed back surgery syndrome. The main ad- vantages of spinal cord stimulation are its minimal inva- Croom JE, Foreman RD, Chandler MJ et al. Cutane- siveness, reversibility and convincing studies to justify its ous vasodilatation during dorsal column stimulation use. In well-selected patients, spinal cord stimulation is is mediated by dorsal roots and CGRP. Am J Physiol cost effective in comparison to conservative treatment ap- proaches. However, further studies are still needed to bet- Gheradini G, Lundenberg T, Cui JG et al. Spinal cordstimulation improves survival in ischemic skin flaps: ter identify patient selection criteria for spinal cord stimu- An experimental study of the possible mediation by calcitonin gene-related peptide. Plast Reconstr Surg1999; 103:1221-1228.
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