Spinal Cord Stimulators

A Comparison of the Trial Period Versus Permanent Outcomes

Ajith Malige, MD; Gbolabo Sokunbi, MD

Disclosures

Spine. 2019;44(11):E687-E692. 

In This Article

Abstract and Introduction

Abstract

Study Design: A retrospective chart review.

Objective: The aim of this study was to address and characterize the differences between pain relief obtained from the "trial" versus permanent stimulator in the acute postoperative period (less than 6 weeks).

Summary of Background Data: After a short stimulator trial (typically less than 7 days), patients who report at least a 50% relief are set up for permanent spinal cord stimulator (SCS) placement. The literature has shown that a subset of patients develop tolerance to these stimulating therapies, often resulting in reduced efficacy of symptom relief as early as 2 years post-permanent implantation.

Methods: Between the years of 2013 and 2017, 241 patient charts who underwent a successful trial and had a subsequent permanent SCS placed by a fellowship-trained surgeon through an open incision were reviewed. For each patient, demographic information, numerical rating system (NRS) pain scores, Oswestry Disability Index (ODI) scores, and opioid medication usage were recorded and stratified by time-period (before trial, after trial and before permanent placement, and after permanent SCS placement).

Results: Of the 100 included patients, 60 were female; 60 patients had previous failed lumbar surgery (53%). Placement of trial stimulator (median = 4) decreased pain scores significantly more than permanent spinal cord stimulator did (median = 2) (P = 0.00). No significant difference was seen in ODI score difference between trial and initial scores (median = 4) and final and initial scores (median = 6) (P = 0.64). Finally, a significantly higher decrease in pain medication usage was seen after trial initiation (median = 0) versus after permanent spinal cord stimulator placement (median = 0) (P = 0.028). Twenty-two patients (22%) had reported complications, with 15 complaining of prolonged surgical site pain.

Conclusion: Discrepancies observed in symptom alleviation between percutaneous trials and permanent placement in the acute 6-week postop period can have a significant effect on patient perceived outcomes. Understanding these issues will help in providing preoperative counseling and managing postoperative expectations.

Level of Evidence: 4

Introduction

Chronic pain syndrome involving the lower back and extremities remains a challenging and expensive problem to address and solve. Neuromodulation of the spine with spinal cord stimulators (SCS) has evolved into a viable technique to address this and other challenging diagnoses. In the 1970s, Shealy et al[1] implanted the first dorsal column stimulator (DCS), aiming to address the "gate control theory of pain" proposed by Melzack and Wall.[2] Since then, neuromodulation, via SCS, has seen significant growth and improvement in both technological design and clinical outcomes. The efficacy of SCS is well documented in the literature.[3–5] They have seen success in scenarios where opioid analgesics and other pain medications,[6] physiotherapy,[7] psychologically based therapies,[8] and transcutaneous electrical nerve stimulation[9] have failed. Although successful treatment is often characterized as a 60% to 70% decrease in baseline pain, the literature continues to show significant heterogeneity regarding accurate documentation of patient outcomes.

SCS do not eliminate the source of pain; instead, they mask it by creating a device-induced paresthesia.[10–15] The overlap between iatrogenic paresthesias, a pre-existing pain patterns, is crucial in successful trialing and permanent therapy. Although it is not fully known why SCS help treat pain in failed back pain syndrome[10,11] and chronic regional pain syndrome,[12,13] most theories point to a suppression of the hyperexcitability of neurons complemented by an increased release of gamma-aminobutyric acid (GABA) and serotonin neurotransmitters to help treat neuropathic pain.[14,15] Interfering with the pain signal to the brain ultimately provides pain relief viavarious mechanisms, such as creating paresthesias through both antidromic and orthodromic activation of collateral fibers.[14] Although low-frequency stimulators (50 Hz) were historically used, high-frequency stimulators (10,000 Hz) became available in 2015. After the SENZA-RCT trial[16] reported an 80% success rate in treatment response (≥50% pain reduction) when using high-frequency stimulators (compared with 40% with low-frequency stimulators), physicians started to more frequently turn to this mode of DCS to help treat their patients' back pain. Even more recently, burst stimulation has shown better control in both the emotional and physical response to pain. These newer modulation modalities have been shown to have improved outcomes over traditional tonic frequency stimulation.[17,18]

A SCS is comprised of a pulse generator, a remote control, and electrodes with conducting wires connecting it to the generator.[19] The generator, which can either be an implantable pulse generator (IPG) or a radiofrequency (RF) receiver, is implanted subcutaneously. The IPG comes in chargeable and nonrechargeable forms. The RF receiver gets its power and pulse settings from an external transmitter. A patient-operated remote control turns the stimulator on and off as well as sets the stimulation pattern based on various current, voltage, and waveform configurations.[20] Finally, the electrodes can be percutaneously placed or through an open incision and a laminectomy.[21]

After undergoing a thorough medical and psychological screening process,[22] patients who are candidates for SCS go through a trial period with a percutaneous stimulator. After a short trial (typically less than 7 days), patients who report at least a 50% relief are set up for permanent SCS placement.[23] Literature suggests that some patients tend to develop tolerance to these stimulating therapies, often resulting in reduced efficacy of symptom relief as early as 2 to 3 years postpermanent implantation;[24,25] however, to date, no study has addressed the commonly reported discrepancies in pain reduction between the trial period and the immediate 6-week postoperative period following permanent placement.

This study aims to address and characterize any differences between pain relief obtained from the "trial" versuspermanent stimulator in the acute postoperative period (less than 6 weeks). The authors believe that in certain patients, there is a potential for clinically significant differences in reported pain relief between the trial and permanent devices. Accurate understanding and characterization of these differences is crucial for improving preoperative counseling while better managing patient expectations, which in turn could help improve outco

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