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9 Articles in Volume 13, Issue #9
Perioperative Pain Plan: Why is it Needed
A Case for Spinal Cord Stimulation Therapy—Don’t Delay
History of Pain: The Nature of Pain
Safe Usage of Analgesics in Patients with Chronic Liver Disease: A Review of the Literature
PROP Versus PROMPT: FDA Speaks
Editor's Memo: Long-Acting Opioids: More Than a Labeling Issue
Use of Long-term Muscle Relaxants
PAINWeek Highlights: Coping Skills, Insomnia, and Opioid Abuse Deterrence
Letters to The Editor

A Case for Spinal Cord Stimulation Therapy—Don’t Delay

Spinal cord stimulation should no longer be considered the treatment of “last resort.” Long-term success rates reach 85% if SCS is performed within 2 years of symptom onset.

No contemporary discussion on the management of chronic pain is complete without consideration of spinal cord stimulation (SCS). SCS has become an attractive addition to the pain management armamentarium because of its unique blend of efficacy supported by Level I evidence,1-6 cost-effectiveness,7 and minimally invasive implantation technique. Moreover, its effects are completely reversible.

SCS involves placement of one or more lead(s), consisting of a longitudinal array of contacts (electrodes), into the dorsal epidural space using either a percutaneous technique or through a small laminotomy. The leads are powered by a battery (implantable pulse generator [IPG]), which delivers pulsed electrical energy. This electrical stimulation produces analgesia by inhibiting nociceptive transmission. A multitude of lead types with varying number of contact points and spacing are now available, enabling precise targeting of the area of pain, while avoiding undesirable stimulation.

The flexibility of the device is further augmented by improved programming capabilities, which allow adjustment of stimulation parameters such as pulse-width, frequency, anode/cathode contact configuration, and amplitude. These parameters are optimized by a neuromodulator and can be further modified by the patient within a specified range through a hand-held programmer.

The Food and Drug Administration (FDA) has approved SCS for treatment of chronic, intractable trunk and limb pain. There is widespread agreement among experts that patients who do not respond to conventional medical management by 12 to 16 weeks should be offered a trial of SCS.8

The mechanism by which SCS produces pain relief has yet to be fully elucidated. Initially, the analgesic properties of SCS were ascribed to Melzack and Wall’s Gate Control Theory. However, this model fails to explain key clinical observations, including the differential success of SCS in neuropathic versus nociceptive pain, lack of efficacy in acute pain, ability of pain relief to outlast stimulation, and the finding that activation of large afferent fibers can at times generate pain.9-11 Current evidence suggests that the mechanism of action of SCS is complex and multifactorial, implicating both spinal and supraspinal pathways (Table 1).9-11

SCS Implantation Pathway

The first step is to identify the etiology of chronic pain that is amenable to SCS. Common indications include failed back surgery syndrome (FBSS), complex regional pain syndrome (CRPS), peripheral vascular disease (PVD), refractory angina pectoris (RAP), post-herpetic neuralgia, cervical radiculopathy following disc surgery, and painful diabetic neuropathy. Novel indications are emerging and include occipital neuralgia, migraine, visceral pain, as well as ilioinguinal, genitofermoral, and intercostal neuralgias.

As noted, SCS should be considered after failure of 12 to 16 weeks of an interdisciplinary, multimodal medical management trial. Treatment should be performed under the supervision of a pain clinic and should include physiotherapy with psychological evaluation and treatment, if indicated. Clinicians should encourage patients to enroll in randomized control trials (RCTs) if eligibility criteria are met. SCS is also utilized in non-pain disorders such as incontinence and visceral motility dysfunction.

Contraindications to SCS

Patient selection is central to SCS outcomes. Although some degree of psychological suffering is expected in patients with chronic pain, any psychological concerns should be addressed prior to implantation. Clinicians must adopt a functional restoration approach, stressing the importance of patients’ returning to active domestic life and gainful employment. Realistic expectations must be fostered—patients must accept that SCS offers symptomatic improvement and does not correct any underlying anatomic deficit or remove the original pathology; pain control is the goal, total abolition of pain is unrealistic.

Contraindications to SCS include untreated severe psychiatric or psychological morbidity, including somatization; non-organic etiology of pain; unwillingness to stop improper drug use; inability to give informed consent or operate equipment; associated coagulopathy, site infection, or sepsis; as well as pending active litigation.

Timing of SCS

In our opinion, SCS should be considered a widely accepted therapy and no longer a treatment of “last resort.” Therefore, early consideration of SCS is warranted. The efficacy of SCS is time-sensitive. There is an inverse relationship between implantation delay and long-term therapeutic success. Long-term success—defined as ≥50% reduction in baseline pain—is attainable in 85% of cases if implantation is achieved within 2 years of symptom onset, but declines to 9% if implantation delay is ≥20 years. Today, the average wait time for SCS implantation is 5.45 years. This has generated long-term success-rates of ~50%.12 A neuromodulation team—consisting of a neuromodulator, pain physician, and nurse—can optimize preoperative care and long-term follow-up.

SCS Trial

The degree of pain control from SCS is difficult to predict based on clinical characteristics. Therefore, all patients being considered for SCS first must undergo a trial procedure. About 15% to 18% of patients fail an SCS trial.12

Figure 1 provides images of a SCS trial in a patient. The procedure can be performed in an outpatient setting under conscious sedation using cylindrical leads placed under fluoroscopic guidance. The lead to be used can be a temporary lead or a permanent lead with an extension; these leads are connected to an external pulse generator. Placement of the leads are as follows:

  • For lower limb pain, the superior electrode should be positioned between T8-T11
  • For upper limb pain, superior electrode is situated between C4-C7
  • For anginal pain, C7-T1 placement is preferred

During intraoperative testing, stimulation-induced paresthesia should cover 80% of the dermatomal distribution of pain, otherwise outcomes are less than optimal. During the trial phase (which averages 1 week), the patient should achieve ≥50% decrease in pain from baseline as proof of efficacy. The patient may adjust stimulation parameters with a hand-held programmer to maximize pain control.

Permanent Implantation

If a patient achieves the desired pain control, he/she goes onto permanent implanation of SCS. If permanent leads were used for trial, they can now be internalized; temporary leads, however, must be discarded. Internalization of the leads is accomplished by anchoring leads to the supraspinous fascia and tunneling them to an IPG, which is surgically placed in the gluteal region or abdominal wall. Both rechargeable and non-rechargeable IPGs are available. The trial log documents power consumption needed to achieve pain control—a strategy that may aid selection of a rechargeable versus non-rechargeable IPG.

The superiority of one lead type over another, optimum number, and spacing of contacts has not been established (Figure 2). Similarly, the superiority of constant current versus constant voltage stimulation is unclear. Clinician preference, technical factors, patient anatomy, and reimbursement policies influence device selection.

Paddle (surgical) leads theoretically offer a more beneficial spatial arrangement and are insulated on the noncontact side. They are more power efficient and carry a reduced risk of displacement or fracturing, but require laminotomy for placement (Figure 3).

Cylindrical leads are placed percutaneously; because of their shape, they induce an electric field 3600 around the electrode, making them less power efficient. Most physicians use cylindrical leads for the SCS trial, and, in general, 80% of permanent implants are done using cylindrical leads.

Bipolar and tripolar configurations provide greater control over laterality of field generation; tripolar configurations enable more precise field steering while avoiding unwanted and annoying radicular paresthesia.9-11

The evidence of the efficacy of SCS therapy is reviewed in Table 2.1-6,13,14 Table 3, lists currently available implantable pulse generators.15-18 A detailed review of implantation techniques are beyond the scope of this article; interested readers are advised to refer to articles in the literature.19

Risks of SCS

Complication rates are highest in the first 6 months of therapy and may occur in up to 32% of cases.1,20 After this period the annual complication rate averages 18%.1,20 In the US, the mean costs for a complication average $9,649 for Medicare and $21,390 for private insurance and annual complication costs averages $1034 (Medicare) and $2293 (Blue Shield).21 Table 4, reviews the incidence, diagnosis and treatment of SCS-related complications.

Future

As with many novel therapies, rapid technological innovation in SCS has outpaced the progression of clinical evaluation. Current trends point towards maximizing contacts per lead, multi-column configurations and lead arrays, enhancing device durability and design, whole body MRI compatibility, IPG miniaturization with improved longevity, discovery of new targets for and modes of stimulation, intelligent programming, and expanding clinical indications to include axial back pain and non-pain therapies. Table 5, reviews the latest developments in SCS.23-27

Conclusions

SCS is gradually gaining traction and wider acceptance. It is an evidence-based therapeutic modality for the treatment of chronic neuropathic and ischemic pain. SCS offers clinical and cost-effective treatment with better long-term outcomes than CMM or re-operation in carefully selected patients.

Case examples

Failed Back Surgery Syndrome

Richard, a 48-year-old self-employed accountant, presents with a 9-year history of persistent low back pain accompanied by bilateral lower extremity pain, which is worse in the left leg. Past medical history is significant for 3 previous lumbar spine surgeries, which included instrumented fusion from L4-S1, and dyslipidemia. The patient’s leg pain is described as burning and dysesthetic (burning, aching, tingling). He denies any bowel, bladder, or sexual dysfunction.

His present medications include hydromorphone immediate-release at 2 mg every 2 hours for breakthrough pain, hydromorphone extended-release 18 mg twice per day, amitriptyline 75 mg at bedtime, duloxetine (Cymbalta) 60 mg once per day, and pregabalin (Lyrica) 75 mg twice per day.

On examination, the patient weighs 84 kg and is 153 cm tall. He is afebrile with stable vital signs. The neurologic exam reveals decreased sensation to pinprick over the anterolateral aspect of the left leg below the knee and extending to the dorsum of the foot and toes, including the big toe. He has intact motor strength and deep tendon reflexes are within normal limits in both legs.

A magnetic resonance imaging (MRI) scan of the lumbar spine showed grade 1 anterolisthesis of L4 on L5, with moderate foraminal stenosis bilaterally. There was severe foraminal stenosis at L5/S1 on the left side and mild stenosis on the right side. In addition, there was evidence of epidural/perineural scar formation at both L4/L5 and L5/S1 levels, with satisfactory hardware placement. Electromyogram (EMG) studies were supportive of L5 radiculopathy.

Richard’s primary care physician referred him to an interdisciplinary pain management clinic where he underwent an intensive 4-month regimen of conventional medical management that included physiotherapy, psychotherapy, epidural steroid injections, and facet joint interventions. Unfortunately, the treatment algorithm failed to significantly improve the patient’s pain levels, functional status, or reduce the need for medications.

The option of SCS trial was discussed with Richard, and he consented to a percutaneous trial that lasted for 1 week. During the trial, he experienced a 60% reduction in pain from his baseline score and an improved ability to carry out daily activities. A permanent SCS system was implanted with dual octapolar leads. Regular follow-up was arranged, initially at 3-month intervals, and subsequently every 6 to 12 months.

Richard continued to report a 50% decline in pain, decreased medication intake—notably opioid consumption—and improved work productivity, walking distance, exercise tolerance, and family and social relationships.

In the discussed case, the beneficial effects of SCS are evident and impressive. With new technology and lead arrangements, harnessing multifocal complex pain patterns—in this case both low back and radicular leg pain—was possible. It is also apparent the wait-times for SCS were exceedingly long, spanning 9 years in Richard’s situation. We predict that had this patient received SCS earlier (≤5 years from pain onset), the degree of pain relief would have been much higher.12 Unfortunately, it remains all too common for patients to undergo repeat lumbosacral spine surgery, despite the law of diminishing returns with iterative operations.

Complex Regional Pain Syndrome

Rebecca, a previously healthy 26-year-old, was employed as a cashier. She accidentally slipped on ice and sustained a fracture of her left ankle. She was assessed in the emergency room and treated with application of a walking cast and given a short course of opioids. Two days later she complained of burning pain on the plantar aspect. Five days later she was unable to stand on her left foot, which had became edematous, erythematous, and hypohidrotic. Rebecca also complained that her left foot felt colder compared with the contralateral limb.

When her walking cast was removed 6 weeks later, Rebecca’s symptoms did not improve. Follow-up radiologic studies showed good alignment and adequate healing of the ankle fracture; however, her pain subsequently intensified. She described her pain as constant and burning over the injury site. She was unable to work.

Upon examination by her primary care provider, it was noted that she had an edematous, discolored (purple), cold left foot, with decreased range of motion, and an inability to bear weight due to severe pain (intensity 7/10). Pulses were present and equal bilaterally, with brisk capillary refill. As noted, X-ray was negative and showed healing of the ankle fracture. Subsequent MRI indicated muscular edema, interstitial edema, and vascular hyperpermeability.

There was no family history of muscle or nerve disease. Social history was negative for smoking or recreational drug use. Rheumatologic blood work was negative for rheumatoid arthritis and lupus. The patient was referred to a neurologist who diagnosed her with complex regional pain syndrome (CRPS).

Rebecca met the International Association for the Study of Pain (IASP) diagnostic criteria for CRPS, with the history of an initiating noxious event (left ankle fracture) followed by immobilization (casting), continuing pain, including hyperalgesia and allodynia, changes in skin and blood flow (mottling of the foot), edema (swollen foot), and vasomotor changes with no other explanation for her symptoms.22 She was started on medical management with carbamazepine 200 mg three times per day, gabapentin was up-titrated to 900 mg three times per day, and verapamil 80 mg twice per day.

The following week, her pain intensity increased and was reported as 9/10. She described excruciating pain with any movement, hyperalgesia, and allodynia—stating that the touch of cloth or even air on her skin provoked pain. The edema and burning had now spread to encompass the lower third of her leg. She was referred to a pain management clinic.

Rebecca’s pain continued to be unrelenting despite a trial of steroids, an increase in gabapentin dose to 3,600 mg/day and high-dose amitriptyline 150 mg at bedtime. Rebecca was unable to show functional improvement despite physiotherapy. Psychotherapy confirmed that there was no significant psychosocial, emotional or psychiatric overlay. Hydromorphone extended-release 12 mg twice per day and hydromorphone immediate-release (4 mg every 2 hours for breakthrough pain) was initiated with no significant benefit achieved. Over the next 3 weeks, 2 sympathetic nerve blocks were performed with transitory pain relief for less than a day. In the ensuing 6 weeks, she underwent 5 epidural blocks with disappointing results.

The option of SCS was discussed, and Rebecca was eager to undergo trial stimulation. During the percutaneous trial she demonstrated an 80% reduction in pain to an intensity of 2 out of 10, accompanied by the ability to walk independently. The edema, temperature, and discoloration of the left foot improved substantially. Permanent placement of SCS was performed. Regular follow-up was arranged. Rebecca continued to report a 75% improvement in pain; decreased medication intake with cessation of opioid use; ability to regain employment; and improved ambulation, exercise tolerance, and social relationships.

The above case illustrates the excruciating nature of pain experienced in CRPS, as well as the difficulty of treating the pain through conventional medical management. The early initiation of SCS not only induced significant pain relief but likely aided her functional improvement, including return to gainful employment. Regular follow-up is warranted as SCS may not prevent spread of CRPS to other body regions. Kemler et al have suggested that the analgesic effect of SCS may diminish after 3 years;4 however, this finding has not been duplicated by others. Kumar et al have shown that in order to maximize functional improvement, implantation should be performed within the first year of symptom onset, in those under 40, and Stage I CRPS, as has been the case here.22

Last updated on: November 21, 2013
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