Spinal Cord Stimulation
Spinal cord stimulation (SCS), sometimes called dorsal column stimulation, describes the use of pulsed electrical energy near the spinal cord to control pain. This technique was first applied in the intrathecal space and later in the epidural space as described by Shealy and associates in 1967. In the present day, neurostimulation commonly involves the implantation of leads in the epidural space to transmit this pulsed energy to the spinal cord or the desired nerve roots. This technique has notable analgesic properties for neuropathic pain states, anginal pain, and peripheral ischemic pain. The same technology can be applied in deep brain stimulation, cortical brain stimulation, and peripheral nerve stimulation. These latter techniques are typically in the realm of the neurosurgeon, although more and more pain physicians are using peripheral nerve stimulation techniques. This chapter concentrates on the modality of spinal cord (dorsal column) stimulation.
Mechanism of Action
Neurostimulation began shortly after Melzack and Wall proposed the gate control theory in 1965. This theory posed that painful peripheral stimuli carried by unmyelinated C fibers and lightly myelinated Aδ fibers terminated at the substantia gelatinosa of the dorsal horn (the gate). Large myelinated Aβ fibers responsible for touch and vibratory sensation also had collateral input to “the gate” in the dorsal horn. It was hypothesized that their input could “close the gate” to the cephalad transmission of painful stimuli. As an application of the gate control theory, in 1967 Shealy implanted the first spinal cord stimulator device for the treatment of chronic pain. This technique was noted to control pain and has undergone numerous technical and clinical refinements in the ensuing years.
Although the gate theory was initially proposed as the mechanism of action, the underlying neurophysiologic mechanisms are not clearly understood. Research has given us insight into effects occurring at the local and supraspinal levels and through dorsal horn interneuron and neurochemical mechanisms. Linderoth and colleagues have noted that the mechanism of analgesia when SCS is applied in neuropathic pain states may be very different from those involved in analgesia as a result of limb ischemia or angina. Experimental evidence points to SCS having a beneficial effect at the dorsal horn by favorably altering the local neurochemistry, thereby suppressing the hyperexcitability of the wide dynamic range (WDR) neurons. Specifically, there is some evidence for increased levels of gamma-aminobutyric acid (GABA) release, serotonin, and perhaps suppression of levels of some excitatory amino acids including glutamate and aspartate. In the case of ischemic pain, analgesia seems to be obtained through restoration of a favorable oxygen supply and demand balance, perhaps through alteration of sympathetic tone. Guan and colleagues made three substantial findings in an in vivo model of SCS and neuropathic pain: (1) stimulation of either the dorsal horn or dorsal nerve roots at intensity and frequency to selectively activate Aβ fibers reduced WDR neurons spontaneous firing in animals with neuropathic injuries; (2) this same stimulation reduced WDR responses to mechanical stimulation of normal and injured animals; and (3) stimulation of the dorsal columns, but not the dorsal root, reduced activity-dependent neuronal excitability (wind-up). Other experimental evidence has suggested that antidromic stimulation from dorsal column stimulation of cutaneous fibers plays a role in the analgesic effect of SCS and possibly the result of antidromic inhibition of orthodromic transmission.
Patient Selection
Patient selection is the most challenging and important step in the decision to offer neurostimulation. Although it can be viewed as a burden or barrier by both the patient and the physician, the additional time dedicated to the selection of patients who are most likely to positively respond to the therapy in the short and long term is time well invested. The challenge pain physicians face is being able to predict who will respond well with durability. There are relatively few data to guide pain physicians in this realm; most of the studies examining who is a good candidate for SCS therapy are small prospective or retrospective studies. In a study examining 36 patients with complex regional pain syndrome (CRPS) treated with SCS, the authors found that mechanical allodynia of the affected limb was negatively correlated with SCS therapy success, and patient age, duration, or intensity of pain had no relationship to SCS outcome. In patients with CRPS, response to a sympathetic nerve block may positively correlate with SCS therapy outcome. Many patients with chronic pain have some symptoms of depression; psychological screening can be extremely helpful for avoiding failed implants in patients with major psychological disorders. An interesting study by Olson and colleagues revealed a high correlation between many items on a complex psychological testing battery and favorable response to trial stimulation. In a systematic review, it was noted that symptoms of depression, somatization, anxiety and poor coping skills were predictors of poor SCS outcome. It appears that overall mood is an important predictor of outcomes. Paradoxically, the psychological construct of catastrophizing, which has been negatively associated with other pain therapies, was not detrimental to the positive SCS outcome in patients with CRPS. Sex and age of patients as well as laterality of pain have also been examined for predictive value and none have been found to impact the results of the SCS therapy. Relatively few randomized controlled studies have been performed that evaluate long-term predictors of success or failure from SCS therapy for specific pain disease processes.
The evaluation of a patient for spinal cord stimulation is a staged process ( Box 69.1 ). Appropriate patients for a trial of neurostimulation must meet the following criteria: (1) the diagnosis is amenable to this therapy (e.g., neuropathic pain syndromes), (2) the patient has failed conservative therapy, and (3) significant psychological issues have been ruled out.
Stage 1: Pain physician visit. This stage is performed to evaluate the pain condition and thereby determine whether the patient’s pain syndrome is amenable to spinal cord stimulation therapy.
Stage 2: Psychological evaluation. This stage is performed to understand the patient’s needs and expectations of therapy.
Stage 3: Trial stimulation. This stage is performed to evaluate the effectiveness of pain reduction (3 to 8 days).
Stage 4: Diagnostic imaging. ∗
∗ This stage may be performed prior to stage 3 (trial implant) if there are clinical signs or symptoms of stenosis or other anatomic impediments to percutaneous cylindrical lead placement.
An MRI will be ordered to determine whether the patient has obstructions within the high lumbar and thoracic spinal space for thoracic placement or cervical space that would lead to concerns about safe lead placement.
Stage 5: Permanent implantation. This may be performed by a neurosurgeon or a pain physician depending on the patient’s comorbidities, pain distribution, or patient preference.
Imaging
Magnetic resonance imaging (MRI) or computed tomography (CT) to determine patency and sufficiency of the high lumbar and low to mid thoracic epidural space should be used to evaluate patients progressing forward to the implantation phase of the thoracic SCS. Ruling out moderate to severe stenosis increases the safety of the procedure. This evaluation may also guide the pain physician’s decision to refer the patient to a surgeon for implantation—for instance, if a surgical decompression is needed prior to implantation of the lead system. Cases of mild (nonoperative) spinal stenosis at the target levels could lead the physician to choose a smaller cylindrical lead rather than the paddle-type leads.
Conservative Therapy
Despite the increase in the number of agents available to treat neuropathic pain, a substantial number of patients still suffer from poorly controlled neuropathic pain. Puig estimates as many as 50% of patients with neuropathic pain have ineffective pain relief even with appropriate pharmacological management. Recommended selection criteria from these authors include (1) confirmed diagnosis of neuropathic pain; (2) chronicity of greater than 6 months; (3) failed trials of polypharmacy including anticonvulsants, antidepressants, and other drugs (such as opioids) because of lack of efficacy or side effects; (4) a lemniscal pathway (spinal connection to painful site) that has been preserved so that stimulation-induced paresthesias can be felt; and (5) the absence of contraindications including nociceptive pain syndromes, psychological disturbance, infection at site, systemic bacterial infections, and a lifestyle that is incompatible with longevity of therapy (patient employed in field requiring excessive repetitive flexion and extension, MRI technician, etc.).
Trial
A careful trial period is essential to avoid a failed implant. Trials of different lengths have been advocated; the risk of a longer trial is mainly infection, whereas the primary risk of too short a trial is a false-positive result. We use a 5- to 8-day trial and encourage patients to be as active as possible in their usual environment, with the exception of limiting bending and twisting movements. In rare circumstances, the author (RWH) uses a permanent trial implantation (discussed later) whereby the percutaneous leads are placed and secured in the same fashion and the entire permanent system is placed with the exception of the implantable pulse generator (IPG); a tunneled lead extension is externalized and connected to the trialing system. Patient selection and physician discretion are exceptionally important in these cases, as there is a natural bias to going forward with the remainder of the implant because of the commitment that has already been made by implantation of the permanent leads. In “perm-trial” cases, the trial period is often much longer than the percutaneous trial, as in this author’s (RWH) experience of up to 3 weeks.
Despite advances in our understanding of diagnoses that respond to neurostimulation, improved psychological screening, and the availability of improved multilead systems, clinical failures of implanted neurostimulator devices remain all too common. Pain physicians must critically evaluate their own outcomes and adhere to the strict selection criterion outlined here. Simpson published a neurosurgeon’s perspective on the use of SCS in treating chronic pain. To paraphrase Simpson,
The mindset of the public and many physicians favors drugs over physical treatments such as surgery and neurostimulation, and many physicians exhibit a “protective” reluctance to refer for these procedures, but are prepared to persist with polypharmacy despite the real risks of mental impairment, nausea, constipation, weight gain, and addiction. The worst thing a neurostimulator can do is fail to work.
Many pain specialists are beginning to side with Simpson on this issue, preferring a trial of SCS before committing a patient to chronic opioid therapy. Although this is true, the corollary is also the case and would suggest caution against the overly liberal application of the technology.
In examining one’s own outcomes with SCS therapy, several factors must be considered:
- 1.
Examination of your trial to permanent ratio data. These data will tell you what percentage of the patients you trial go on to have a permanent implantation. All things being equal (with the assumption that all permanent implantations were the correct decision) this ratio will give a hint to your ability to select appropriate patients for this therapy. A ratio below 50% would suggest you are not being selective in your application of the therapy, and a ratio of 95% would suggest you are being too selective and more than likely not offering the therapy to those who could benefit.
- 2.
Examination of your permanent implantation data:
- a.
Number of patients who continued to use the SCS in the long term
- b.
Number of patients who had the permanent system removed
- c.
Number of surgical site infections (within 1 year of implant) and proximate cause
- d.
Number of clinically significant migrations
- i.
How many were resolved with re-programming
- ii.
How many were resolved with re-operation
- i.
- e.
Number of other adverse events (not already listed)
- a.
- 3.
Long-term pain relief success of therapy. This applies to follow-up with your SCS patients at regular intervals to reassess their success or lack thereof. A common interval recommended is every 6 months to every year (at the maximum).
- 4.
Assessment of other quality-of-life indicators:
- a.
Improvement in activities of daily living (household chores, fitness activities)
- b.
Improvement in psychological factors (mood, pain coping, anxiety)
- c.
Improvement in patients’ sleep, personal relationships
- a.
- 5.
Assessment of medication intake. What reductions in pain medication have occurred? (Have you, as the physician, addressed this issue and attempted to wean medications?)
Technical Considerations
SCS is a technically challenging interventional/surgical pain medicine technique. It involves the placement of an electrode array (leads) in the epidural space, a trial period, anchoring the lead(s), positioning and implantation of the pulse generator or radiofrequency (RF) receiver, and the tunneling and connection of the wires. This is one of the more complex procedural skills in pain medicine and is an excellent example of why pain medicine is a subspecialty of the practice and should not be performed by a nonphysician or non-pain medicine trained physician.
A spinal cord stimulator system is made up of three parts: (1) electrodes or leads ( Fig. 69.1 ), (2) IPGs or the battery ( Fig. 69.2 ), and (3) the charging and programming systems (see Fig. 69.2 ). Electrodes are of two types: cylindrical (formerly known as percutaneous) and paddle (formerly known as surgical) (see Fig. 69.1 ). These electrodes are connected to an IPG or (historically, but no longer available) an RF unit. Currently, three companies—Medtronic, Inc., St. Jude Medical, Inc., and Boston Scientific Corp. (formerly Advanced Bionics, Inc.)—make neurostimulation equipment ( Appendix A ). Historically the paddle-type lead could only be implanted via a laminotomy or more extensive laminectomy. In 2011, one neuromodulation company introduced a system by which a surgical paddle lead (single 8-contact column) could be implanted in a percutaneous fashion using a wide flat introducer that is placed via the Seldinger technique ( Fig. 69.3 ). This has allowed advanced pain physicians who are not spine surgeons to take advantage of these lead systems.
A spinal cord stimulator trial may be accomplished in two ways: percutaneous or permanent lead trial. In both trial methods, under fluoroscopy and sterile conditions ( Table 69.1 ), a lead is introduced into the epidural space with a standard epidural needle or curved epidural needle. To facilitate threading of the lead cephalad in the dorsal midline region, it is imperative to have the needle at a shallow angle (often less than 45 degrees). It is essential to avoid perpendicular or near perpendicular needle placement into the epidural space (unless using a curved needle) because of the consequent 75- to 90-degree bend then required to introduce the stimulator lead. The lead is directed under fluoroscopic imaging into the posterior or dorsal paramedian epidural space up to the desired anatomic location—generally the low thoracic cord region (commonly T8 to T10) to obtain paresthetic coverage of the lower extremities or the midcervical level to obtain coverage of the upper extremities (i.e., the lead is moved cephalad and caudad in the epidural space until the pattern of resulting electrical stimulation overlies the painful region; Fig. 69.4 ). Trial stimulation is undertaken to attempt to cover the painful area with an electrically induced paresthesia. After the painful area is captured with either one or more leads, the two techniques of trialing differ.
| Surgeon | Patient | Instruments | |
|---|---|---|---|
| Percutaneous Trial Lead | Hair coverage, eye protection | Pre-procedure chlorhexidine shower | Sterile covering for fluoroscopic machine |
| Surgical scrub | Sterile skin preparation with alcohol-based chlorhexidine scrub | Lead kit from company | |
| Sterile gown, gloves | Towels and full surgical drape | ||
| Bio-patch (chlorhexidine) application | |||
| Permanent or Perm Trial Lead | Hair coverage, eye protection | Pre-procedure chlorhexidine shower | Sterile covering for fluoroscopic machine |
| Surgical scrub | Pre-operative antibiotics for coverage of skin flora (cefazolin or clindamycin) | Lead kit from company | |
| Sterile gown and gloves | Sterile towelsIodine-impregnated adhesive dressing (unless iodine allergic)Full surgical drape | Implantable pulse generator (IPG) from company (if IPG implantation is intended) |
In the percutaneous trial, the needle is withdrawn, the lead is adhered in place (with a suture, surgical skin glue, or surgical adhesive), a chlorhexidine impregnated patch (RWH) and a sterile dressing is applied. The lead passes from the epidural space, through the skin to the external pulse generator throughout the trial period. When the patient returns after a trial of several days, the dressing is removed, and the lead is removed and discarded regardless of the success of the trial. When the patient returns for an implant, a new lead is placed in the final location of the trial lead contacts and connected to an IPG.
In the permanent lead trial, after successful positioning of the trial lead(s), local anesthetic is infiltrated around the needle(s) and an incision is made, cutting down to the supraspinous fascia to anchor the leads securely using nonabsorbable suture. The anchoring device should be placed as closely as possible to the fascia entry site, ideally with the “nose” of the anchor protruding into the fascia to lessen the bending angle of the lead. The anchor is secured using nonabsorbable suture, such as 2.0 silk. At this point, two approaches can be used. The first method requires opening up the midline back incision. In this technique, the proximal end of a temporary extension wire is connected to the permanent lead, and the distal end is tunneled away from the back incision and out through the skin. The second method does not require reopening the midline back incision; instead a pocket for the IPG is created. With this technique, the IPG pocket is created and the permanent lead is tunneled to this pocket; an extension lead is then connected to the permanent lead and the distal end is tunneled away from the IPG pocket. The IPG pocket is then sutured closed. With either technique, this exiting connector is secured to the skin using a suture (or surgical skin glue), antibiotic ointment, and a sterile dressing. If the trial is successful, at the time of implant the back incision (or IPG site incision) is opened and the percutaneous lead extension is cut, pulled out through the skin site, and discarded. The permanent lead(s) that was used for the trial is attached to a new sterile extension(s) (not needed if at the IPG site) and tunneled (or directly connected) to the IPG.
The permanent lead trial method has the advantages of saving the cost of new electrodes at implant and ensuring that the implanted lead position matches the trial lead position. Advantages of the “percutaneous lead” approach include avoiding the costs of two trips to the operating room (even for an unsuccessful trial, this is necessary to remove the anchored trial lead); avoiding an incision and postoperative pain during the trial, which may confuse trial interpretation by the patient; and avoiding the risk of infection associated with the percutaneous temporary extension. The percutaneous extension must be anchored and meticulously dressed or the risk of infection may be higher than with the straight percutaneous technique. The majority of clinicians favor the percutaneous trial method. Most consider 50% or more pain relief to be indicative of a successful trial, although the ultimate decision also should include other factors such as activity level and medication intake. Some combination of pain relief, increased activity level, and decreased medication intake is indicative of a favorable trial.
A trial with paddle-type electrodes (with the exception of the previously mentioned percutaneous paddle introduction technique) requires the implanted lead approach with the significant addition of a laminotomy to slip the flat plate electrode into the epidural space. Some physicians trial the patient with the percutaneous approach and if successful send the patient to a neurosurgeon for a paddle-type implant.
The IPG is generally implanted in the flank, occasionally in the posterior superior gluteal area or rarely the lower abdominal area or pectoral region. It should be in a location the patient can access with the dominant hand for adjustment of the settings with the patient-held remote control unit. The decision to use a rechargeable implantable IPG is based on several considerations. If the patient’s pain pattern requires the use of many anode or cathode settings with high power requirements during the trial, consider a rechargeable, higher-capacity unit. The IPG battery life largely depends on the power settings used, but the newer IPG units generally last several years at average power settings. All three manufacturers offer rechargeable IPG systems with two significant advantages over the previous IPG devices: (1) the patient may use higher voltage settings without worry of prompt battery depletion, allowing more flexibility in programming, and (2) the promise of a much longer interval until replacement is required, perhaps 10 years or more. The unit is recharged via an external recharger every 7 to 14 days as needed.
Complications
Complications associated with spinal cord stimulation range from simple, easily correctable problems—such as lack of appropriate paresthesia coverage—to devastating paralysis, nerve injury, and death. Prior to implantation of the trial lead, an educational session should occur with the patient and family members. This meeting should include a discussion of possible risks and complications. In the postoperative period, the caregiver should be involved in identifying problems and alerting the health care team.
North and colleagues reported their experience in 320 consecutive patients treated with SCS between 1972 and 1990. A 5% rate of subcutaneous infection was observed, which is consistent with other published trials. The most frequent complication was lead migration or breakage, and that remains the predominant weakness of neurostimulation. The revision rate for patients with modern multichannel devices was 16%. Failure of the electrode lead was observed in 13% of patients and steadily declined over the course of the study as the lead systems were modernized. When analyzed by implant type (single-channel percutaneous, single-channel laminectomy, and multichannel), the lead migration rate for multichannel devices was approximately 7%. Analysis of hardware reliability for 298 permanent implants showed that technical failures (particularly electrode migration and malposition) and clinical failures had become significantly less common as implants had evolved into programmable, multichannel devices and anchoring technique and equipment have improved.
Occasionally, a short-lived series of SCS complications can occur at sites. In 2008, an outbreak of staphylococcus aureus infections related to interventional procedures including SCS resulted in temporary closure of a private pain practice. Other outbreaks of infection have been noted during quality assessments of current practices. One such assessment of the experience at the Johns Hopkins Pain Clinic in 2010 revealed that, during a 6-month period in 2010, five patients with SCS trial lead implantations became infected as compared to one trial lead in the previous 3.5 years. The median time to infection diagnosis was 4.5 days. The infections associated with the five trial lead infections in 2010 ranged from superficial cellulitis to radiographically confirmed epidural abscess. Unfortunately, no independent risk factors (implanting pain fellow, SCS company, use of pre-operative antibiotics, lead location, or patient comorbidities) were identified as the causative agent.
In a 5-year experience prior to 2006 at the Cleveland Clinic, Rosenow and colleagues reported a 43% revision or removal rate among 289 patients implanted with SCS systems. Thirty-three percent of all leads required revision, with the most common reasons being lead breakage, poor pain coverage, migration, and infection in descending order of frequency. Ten percent of patients had a lead migration requiring revision. Paddle-type leads broke twice as often as percutaneous leads. Twenty-two percent of all patients required more than one revision procedure; 49% requiring at least one lead revision underwent multiple revisions. Anatomically, cervical leads were the most likely to require revision. Their overall infection rate was 3.6%. This experience was somewhat exceptional and the data are no longer current, so they are included only for historical guidance. A more recent retrospective review from the same institution shows the progress made in SCS therapy complication rates. In this review, the only documented complication associated with SCS trials was lead migration in 5 of 707 patients (0.7%). There were no permanent neurologic deficits or deaths as a result of SCS permanent implantation. The most common complications were hardware related (38% of all complications) and included lead migration (22.6%), lead connection failure (9.5%), and lead breakage (6%). Revisions or replacements were required in these cases. Related complications included pain at the generator site (12%) and clinical infection (4.5%; 2.5% with positive culture). The rates of infection varied among the different diagnoses with the highest in failed back surgery syndrome (6.3%). Patients with diabetes had an infection rate of 9%, over the 4% rate in nondiabetics. Infections were managed successfully with explantation and antibiotic therapy without permanent sequela.
May and coworkers and Barolat and associates reported lead revision rates caused by lead migration of 4.5% and 13.6% and breakage of 0% and 13.6%, respectively. Infections occurred in 7% and 2.5% of cases, respectively. No serious complications were observed in either study. These studies are representative of the complication rate of neurostimulation therapy. Kumar and colleagues in Saskatchewan have quantified the costs of SCS complications and published suggestions to improve outcomes. Their series included 160 patients treated over 10 years with SCS implantation. They noted 42 patients with 51 complications classified as hardware related (39) or biologic (12) with the range of costs of treatment from $130 (hematoma aspiration) to $22,406 (system reimplantation) (in 2005 Canadian dollars). Their most common hardware failures were lead displacement (11% of patients), followed by fractured electrode (5.6% of patients). Their most common biologic complication was wound infection at 4.4% overall, with subcutaneous hematoma next at 3% overall. These authors presented an analysis of engineering work done at Medtronic, Inc. with regard to lead migration and fracture. This manufacturer recommends the use of a silicon anchor (not hard plastic) with the tip of the anchor pushed through the deep fascia to reduce the pressure point or fatigue point on the lead with repeated bending. Further, the manufacturer recommends a strain relief loop between the anchor and the IPG, with the flank being the preferred site of IPG implant because of less stress on the leads during bending. Another poorly understood phenomenon described by Kumar is late tolerance to stimulation in 16 of 160 patients (10%).
Infections range from simple infections at the surface of the wound to epidural abscess. The patient should be instructed on wound care and recognition of signs and symptoms indicative of infection. Many superficial infections can be treated with oral antibiotics or simple surgical incision and drainage followed by wound irrigation. For an excellent review on infectious complications of SCS, the reader is referred to Follett and colleagues’ review of 114 cases with recommendations for avoidance. They found that the most common sites of infection were the IPG (54%), the connector tract (17%), and the back incision (8%). Staphylococcus species were the most common pathogen, cultured in 18% of cases, with system explant required in 82% of cases. One death related to infection and one case of epidural abscess leading to paralysis caused by SCS have been reported. Standard practice includes prophylactic preoperative antibiotics (30 minutes pre-incision).
If infection reaches the tissues involving the devices, in most cases the implant should be removed. In such cases, one should have a high index of suspicion for an epidural abscess. Abscess of the epidural space can lead to paralysis and death if not identified quickly and treated aggressively. The likelihood of epidural abscess from a percutaneous SCS trial is exceptionally low, although exceptions do exist.
Programming
There are four basic parameters in neurostimulation that may be adjusted to create stimulation paresthesias in the painful areas, thereby mitigating the patient’s pain. They are amplitude, pulse width, rate, and electrode selection.
Amplitude is the intensity or strength of the stimulation measured in volts. Typically, voltage may be set from 0 to 10 volts, with lower settings used over peripheral nerves and with paddle-type electrodes. Pulse width is a measure in microseconds (µs) of the duration of a pulse. Pulse width is usually set between 100 and 400 µs. A larger pulse width typically gives the patient broader coverage. Rate is measured in hertz (Hz) or cycles per second, between 20 and 120 Hz. At lower rates the patient feels more of a thumping, whereas at higher Hz the feeling is more of a buzzing. Electrode selection is a complex topic that has been the subject of research by Barolat and colleagues, who provided mapping data of coverage patterns based on lead location in 106 patients. The primary target is the cathode (−), with electrons flowing from the cathode(s) (−) to the anode(s) (+). The newest stimulator systems allow for partial anode and cathode arrangements at different contacts, which have been termed “current steering.” This expands the ability to cover most painful areas with a well-placed lead or leads and makes the number of possible configurations available for programming almost infinite. Thus, a programming strategy is important, and each company has developed computer-assisted programming to narrow down the possible choices. Most patients’ stimulators are programmed with electrode selection changes until the patient obtains anatomic coverage, then the pulse width and rate are adjusted for maximal comfort. The patient is left with full control to (1) turn the stimulator on and off, (2) choose between numerous programs in the device (which have different effects), and (3) adjust the intensity of stimulation up and down for comfort.
The lowest acceptable settings on all parameters are generally used to conserve battery life unless using the newer rechargeable systems. Other programming modes that save battery life include a cycling mode during which the stimulator cycles full on and off at patient-determined intervals (minutes, seconds, or hours). The patient’s programming may change over time, and reprogramming needs are common. The neurostimulator manufacturing companies help clinicians with patient reprogramming. Many busy pain practices designate a nurse practitioner or physician’s assistant to handle patient reprogramming needs.
Outcomes
The most common use for SCS in the United States is failed back surgery syndrome (FBSS), whereas in Europe, peripheral ischemia is the predominant indication. With respect to clinical outcomes, it makes sense to subdivide the outcomes based on diagnosis ( Boxes 69.2 and 69.3 ). There have been prospective randomized controlled trials (RCTs) examining SCS therapy in FBSS, CRPS, angina, and peripheral vascular disease (PVD) meeting Class II evidence requirements. However, in a review of the available SCS literature, most evidence falls within the Class III (limited) category, as a result of the invasiveness of the modality and difficulties inherent in blinding treatment with SCS, because much of the available literature used older technologies. Recognition must also be given to the time frame within which a study was performed because of rapidly evolving SCS technology. Basic science knowledge, implantation techniques, lead placement locations, contact array designs, and programming capabilities have changed dramatically from the time of the first implants. These improvements have led to decreased morbidity and a much greater probability of obtaining adequate paresthesia coverage with subsequent improved outcomes. For these reasons the literature on SCS outcomes is limited to year 2000 to the present day. Coffey and Lozano, among others, called for future study designs to include unambiguous entry criteria, randomization, parallel control groups receiving sham treatment, and blinding of patients, investigators, and programmers. They also suggested a minimum follow-up time of 1 year for chronic pain conditions, with a Kaplan-Meier–type analysis of ongoing pain relief.
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