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NEUROMODULATION FOR FAILED BACK SURGERY SYNDROME IS THE WAY FORWARD!: CON
Author(s):
Kapural, L.*
Affiliations:
Carolinas Pain Institute, Anesthesiololgy, Winston-Salem, USA
ESRA Academy. Kapural L. Sep 16, 2017; 195893
Topic: Nerve Stimulators
Leonardo Kapural
Leonardo Kapural

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Learning Objectives
Abstract
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After viewing this presentation the participant will be able to:

- Recognize shortcomings of studies showing favourable results of spinal cord stimulation
- Identify disadvantages of spinal cord stimulation including loss of effectiveness and explant rates

Failed back surgery syndrome (FBSS) is present in about 30% of the patients who have undergone surgery involving the discs of the lumbar spine.1 It is characterized by maintenance of a chronic painful state, wherein the original back pain source(s) was either not properly addressed by the surgery or an additional idiopathic source of pain existed that could not be treated by such a surgical intervention. FBSS may also describe patients that have acquired a new back pain condition after spinal surgery.

 

Various therapeutic approaches are currently used to treat refractory chronic back and leg pain after spinal surgery.1  Presently, spinal cord stimulation (SCS) is considered as a relatively late stage treatment for FBSS.1-6 This utilization late in the continuum of care is surprising as both Level 1 and Level 2 evidence exists indicating traditional SCS is a safe, clinically-effective and cost-effective treatment.7-9 Technological advancements such as novel waveforms, higher stimulation frequencies and new anatomical targets have vastly expanded the field of SCS, resulting in greater effectiveness and broader applicability of this treatment. Additionally, these approaches may provide a rescue treatment for patients who have previously failed surgical and less invasive therapies, offering relief to a patient population among the most difficult to treat.

 

Although evidence supports its safety and efficacy, traditional low-frequency stimulation produces unpleasant paresthesias in 49-71 % of patients, causing sudden surges and shocks that may become less tolerable over the time .2-9 Persistent paresthesias associated with low-frequency SCS and loss of efficacy from other unknown causes may result in attrition or “tolerance” in FBSS patients. 

SCS for the treatment of chronic pain is becoming a fast advancing field of neuromodulation. Thus, it is difficult to predict how and where evidence shall lead the field over the next 5-10 years when it comes to various stimulation frequencies and modalities of SCS treatments for FBSS. This article will provide an overview of current evidence and highlight recently published new waveform studies that have produced genuine excitement in the field of neuromodulation.

 

One of the most studied indications for SCS is FBSS in the form of persistent radicular pain after any lumbar disc surgery. When it comes to use of traditional low-frequency SCS for FBSS, two randomized controlled trials and numerous retrospective studies have been published. Summarizing data collected over more than 25 years, traditional low-frequency SCS at any given time interval provides approximately 50% pain relief in about 50% of the patients. Outcomes remain unchanged from an early SCS era (before 1995; 2,9) until now.10-12

 

The two most cited, and the only randomized prospective trials on the use of traditional low-frequency SCS specifically for FBSS, are those from North et al. and Kumar et al.7-9 In addition, recently Kapural et al.4,10 provided further evidence for both traditional and high-frequency SCS at 10 kHz treatment of back and leg pain in a prospective, randomized comparative study with long-term outcomes. North et al.7 enrolled 50 subjects in a crossover study, treating subjects with either SCS or spinal revision surgery. Forty-five of those subjects were followed for up to 3 years. Nine of 19 subjects (47.4%) with SCS and 3 of 26 subjects (11.5%) that underwent repeated surgery had greater than 50% pain relief. The crossover rate was lower in the SCS group than in the group receiving additional surgery (5/24 vs. 14/26, respectively), indicating patient preference for SCS over repeated surgery.7

 

Dr. Kumar and his group studied 100 patients who had predominant neuropathic leg pain after spinal surgery in the PROCESS study.8,9 Patients were randomized to either receive maximal conventional medical management (CMM), or maximal CMM plus SCS. At 6 months, 48% of the patients who had been treated with SCS had more than 50% pain relief, while only 9% in CMM group reported similar pain relief. The crossover rate at 6 months was much lower in the SCS group. Moreover, at 6 months, patients randomized to SCS achieved significantly greater improvement in functional capacity and quality of life compared to CMM patients.  Long-term follow up of 12 months reported in Kumar et al. (2007)8 demonstrated that the SCS group experienced improved pain relief, better quality of life and functional capacity, as well as greater treatment satisfaction than the CMM group (p ≤ 0.05). At 24 months9, 37% of patients in the SCS group continued to achieve at least 50% pain relief vs. 2% of patients in the CMM group (p = 0.003).

 

The two clinical studies of 10 kHz SCS provided consistent set of data, and much better clinical efficacy4,10 than traditional SCS setting a new efficacy standard that emerging waveform modalities of SCS should match or exceed. Based on the current status of clinical evidence, paresthesias during SCS are not essential for pain relief and have proven to be uncomfortable, limiting the acceptable time interval and amplitude of low-frequency stimulation.

 

Burst stimulation utilizes complex programming to deliver a 40 Hz burst mode, each burst consisting of 5 spikes at 500 Hz per spike delivered in a constant current mode.13 Using this methodology, paresthesia-free stimulation can be achieved in > 80% of the patients.  It was suggested that burst stimulation may specifically activate lateral perceptive pathway and the medial pathway by activating the dorsal anterior cingulate and the right dorsolateral prefrontal cortex, and that was modulating the affective component of pain13 .There is no direct evidence on such differential effect of burst stimulation.

 

SCS has been under peer and public scrutiny because of possibility of severe complications related to nerve damage, bleeding or infection.  The occurrence of the most common complications of SCS for FBSS, including uncomfortable paresthesias, pain at the implantation site, and lead migration, have drastically decreased over the last 5 years. Using more portable systems, better anchors and anchoring techniques, and better practice guidelines may influence the rate of complications.     

 

Infection, either superficial, deep, or epidural abscess is the most concerning complication of SCS system implantation. Wound dehiscence and/or device erosion, and presence of seroma may relate to surgical technique and patient’s co-morbidities. Neuroaxial hematoma is rare, but a serious complication of SCS implantation. Currently, proper guidelines exist for management of a patient on anti-coagulation medications. Nerve damage including quadriparesis has been described in literature. Dural puncture and headache are common complications observed when the typically large, 14G, needle placement into the epidural space erroneously advances intrathecally, producing a so called “wet tap”. Other complications are less frequent and include immunologic reactions, epidural fibrosis, renal failure, nausea or even diarrhea.14,15

 

 

Psychosocial evaluation for implantable devices requires detailed testing inventories, but should also explore patient expectations, presence of psychological disease, and barriers to proposed treatment.16 Such evaluation improves long-term outcomes of SCS. Long et al. reported a 33% success rate of SCS trialing in psychologically “unscreened” patients and a 70% rate in “screened” patients.17 North et al. 18suggested that certain psychological variables are associated with pain relief during the trial, after implant, but not at longer follow-up. Proper assessment of pain relief, improvement in function, and patient satisfaction during the trial together may improve its predictive value.19 Mood disorders such as depression and anxiety are the most common psychological co-morbidities associated with disabling medical conditions and may not be obvious because of an individual’s adaptive coping. Therefore, in addition to regular assessments, psychological interventions may need to be implemented before trialing, or post-implantation of the system. Patients with somatization disorders or emotional reactivity may be more likely to have a positive trial followed by ineffective SCS therapy.18 Intolerance to paresthesias, when traditional low-frequency SCS is used, is more likely in those with somatic preoccupation, hysteria, obsessive–compulsive tendencies and anxiety upon psychological testing19

 

References

  1. European Journal of Pain Supplements 2010;4:273-86.
  2. Spine (Phila Pa 1976) 2005;30:152-60.
  3. Pain 2004;108:137-47.
  4. Anesthesiology 2015;123:851-60.
  5. Neuromodulation: Technology at the Neural Interface 2016;19:398-405.
  6. Neuromodulation 2014;17:152-9.
  7. Neurosurgery 2005;56:98-106; discussion -7.
  8. Pain 2007;132:179-88.
  9. Neuromodulation 2005;8:213-8.
  10. Neurosurgery 2016;79:667-77.
  11. Pain Physician 2009;12:379-97.
  12. Pain Physician 2016;19:E33-34.

    13. World Neurosurg 2013;80:642-9 e1.
    14. Neuromodulation 2014;17:571-97; discussion 97-8.
    15. Curr Pain Headache Rep 2014;18:406
    16. Neuromodulation 2006;9:290-308.
    17. Neurosurgery 1985;17:773-7.
    18. Neurosurgery 1996;39:301-10; discussion 10-11
    19. Neuromodulation. San Diego: Academic Press, 2009:69-80.

 

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