Pain is an important factor in determining a patient’s quality of life. Recent years have seen a trend toward nonpharmacologic treatment of pain, which has occurred secondary to the increasing evidence of the lack of efficacy of opiates and other pain medications. Current Centers for Disease Control and Prevention (CDC) guidelines for pain management recommend nonpharmacologic and non-opiate pharmacologic management of chronic pain symptoms.^[1] Neuromodulation, specifically spinal cord stimulation (SCS), presents a viable option for nonpharmacologic management of a subset of patients suffering from chronic pain. However, as with any treatment modality, associated risks accompany the benefits of SCS.

Complications, however, are estimated to range from 30%–40% and can be divided into two categories: device-related failure or biologic factors.

SCS is thought to be a safe, minimally invasive procedure for management of a variety of painful conditions. Complications, however, are estimated to range from 30%–40%^[2],[3] and can be divided into two categories: device-related failure or biologic factors. Device-related complications consist of lead migration, lead breakage, over or under stimulation, intermittent stimulation, hardware malfunction, loose connections, battery failure, and failure to communicate with the generator. Biologic complications include infection, epidural hemorrhage, seroma, paralysis, cerebrospinal fluid (CSF) leakage, pain over implant site, allergic reaction, and skin breakdown.^[2]

Device-Related Complications

In 2014, Deer et al further separated device-related complications into two categories: hardware failure and battery failure.^[4] Hardware failure is primarily associated with the lead and often described by patients reporting a change in device stimulation. Lead fracture or disconnect occurs in 5.9%–9.1% of devices and is diagnosed through imaging of the lead or checking lead impedances.^[3],[5]

Lead migration is the most common complication of SCS. In 2004, Cameron conducted a 20-year literature review demonstrating a lead migration rate of 13.2%.^[2] More recent literature reviews reported higher rates, ranging from 20%–22.6%.^[5],[6] Paddle electrodes may have a decreased risk of lead migration but an increased rate of immediate postoperative complications, such as neurologic injury and epidural hematoma.^[7] Other studies have shown comparable lead migration rates between paddle and percutaneous leads.^[8] The major issue with lead migration is impairment of SCS function, leading to revision, replacement, or explant of the device, thus increasing the risk of further complications.

Battery failures are less common than lead failures, although much less information is available in the literature, especially for newer, rechargeable systems.^[4] Cameron’s review showed a 1.7% battery failure rate, but nearly 69% of those occurred after three years, which may be indicative of battery life versus true failure rate.^[2] The best way to assess for battery failure is to have the manufacturer representative evaluate the device.

Biologic Complications

Biologic complications present a larger concern for practitioners. However, they occur at a lower frequency than device-related complications.^[2] Biologic complications include infection following SCS implantation, neurologic injury, epidural hematoma, skin erosion, epidural fibrosis, dural puncture, pain, and allergic reaction to the device.^[9]

The most significant biologic complication results from implanting the SCS device. Infections can develop in the superficial, deep, and epidural levels but most commonly in the pocket site created for the implanted generator. Infection rates range from 2%–10% based on multiple retrospective and randomized controlled studies.^[9] However, in a recent multicenter, retrospective review, Hoelzer et al looked at 2,737 SCS implants and found an overall infection rate of 2.45%.^[10] In the surgical literature, diabetes, tobacco abuse, and obesity have been identified as the most common risk factors for surgical site infections. However, Hoelzer et al found that those comorbidities did not increase the risk of SCS-specific surgical site infections; instead, the review demonstrated a significant decrease in infection rates with the use of postoperative occlusive dressings and postoperative antibiotics.^[10]

Interest is increasing in developing methods to reduce infection at the pocket site. Clinicians have started placing vancomycin powder or multidrug eluding envelopes at the pocket site to help reduce the infection rate based on evidence from the neurosurgical and cardiac literature.^[11],[12] However, the SCS literature has no consensus to recommend routine use of those methods. The most current guidelines about recommended practices to reduce surgical site infections—released in 2016 at the Neurostimulation Appropriateness Consensus Committee (NACC)—coincide with the CDC guidelines for prevention of surgical site infections.^[13]

Another low frequency postoperative complication is a neuraxial hematoma, which can result in significant debility. The rate of epidural hematoma occurrence is reported in the literature as 0.25%–0.3%,^[2],[14] and they often present with progressive weakness and sensory deficits. Until recently, no consensus guidelines were available for anticoagulation and SCS placement. In 2017 and 2018, NACC and ASRA released SCS anticoagulation guidelines that identified that SCS implantation puts patients at high to intermediate risk for bleeding complications and provided recommendations for stopping and restarting anticoagulation.^[15],[16] Although the guidelines present a framework for decision-making, the procedure’s elective nature requires a patient-centered discussion of risks versus benefits.

Another uncommon complication is neurologic injury. Neurologic injury can consist of motor, sensory, or autonomic changes and may result from direct trauma to the nervous system from the needle, lead, or paddle. Delayed neurologic damage can occur from epidural hematoma and infection. Reported rates of neurologic injury have been low, ranging from 0.03%–0.25%,^[2],[14] although a recent study by Petraglia et al indicated a higher rate of 2.35%.^[17] The variability highlights the importance of risk stratification for SCS candidates to prevent neurologic injury. Risk can also be reduced by adherence to NACC guidelines for reduction of severe neurologic injury.^[18] 

Other risks are associated with the provision of periprocedural sedation. A significant proportion of trials and permanent implants are performed without neuromonitoring but with patients under varying degrees of sedation. Most rely on fluoroscopy and sedated patients’ responses to indicate and protect against intraoperative injury to nervous tissue. Falowski et al described a novel method to improve safety and accuracy using fluoroscopy and neuromonitoring during lead placement, which allows for general anesthesia throughout the procedure while monitoring for CNS injury. The method can also confirm lead placement in the correct anatomic location in the spinal column, leading to safer and more easily tolerated procedures.^[19]

Although SCS is a viable, nonpharmacologic alternative for pain management, it has a variety of complications with varying degrees of frequency. The most common complications result from device-related issues. These are somewhat outside the control of the provider and are not typically associated with significant morbidity. Providers should be knowledgeable of the possible biologic risks to appropriately select patients for SCS trials, employ methods to prevent complications, and diagnose and treat any developing complications early, thereby reducing the risk of long-term neurologic injury.

References

1. Centers for Disease Control and Prevention. CDC guideline for prescribing opioids for chronic pain. December 5, 2017; https://www.cdc.gov/drugoverdose/prescribing/guideline.html. Accessed April 29, 2018.
2. Cameron T. Safety and efficacy of spinal cord stimulation for the treatment of chronic pain: a 20-year literature review. J Neurosurg. 2004;100(3 Suppl Spine):254–267.
3. Kumar K, North RB, Taylor RS, et al. Spinal cord stimulation versus conventional medical management: a prospective, randomized, controlled multicenter study of patients with failed back surgery syndrome (PROCESS study). Neuromodulation. 2005;8(1-2):213–218. https://doi.org/10.1016/j.pain.2007.07.028
4. Deer TR, Mekhail N, Provenzano D, Pope J, et al. The appropriate use of neurostimulation: avoidance and treatment of complications of neurostimulation therapies for the treatment of chronic pain. Neuromodulation. 2014;17(6):571–598. https://doi.org/10.1111/ner.12206
5. Kumar K, Hunter G, Demeria D. Spinal cord stimulation in treatment of chronic benign pain: challenges in treatment planning and present status, a 22-year experience. Neurosurgery. 2006;58(3):481–496. https://doi.org/10.1227/01.NEU.0000192162.99567.96
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7. Babhu R, Hazzard M, Huang K, et al. Outcomes of percutaneous and paddle lead implantation for spinal cord stimulation: a comparative analysis of complications, reoperation rates, and health-care costs. Neuromodulation. 2013;16(5):418–427. https://doi.org/10.1111/ner.12065
8. Rosenow JM, Stanton-Hicks M, Rezai AR, et al. Failure modes of spinal cord stimulation hardware. J Neurosurg Spine. 2006;5(3):183–190. https://doi.org/10.3171/spi.2006.5.3.183
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14. Levy R, Henderson J, Slavin K et al. Incidence and avoidance of neurologic complications with paddle type spinal cord stimulation leads. Neuromodulation. 2011;14(5):412–422. https://doi.org/10.1111/j.1525-1403.2011.00395.x
15. Deer TR, Narouze S, Provenzano D, Pope J, et al. The Neurostimulation Appropriateness Consensus Committee (NACC): recommendations on bleeding and coagulation management in neurostimulation devices. Neuromodulation.  2017;20(1):51–62. https://doi.org/10.1111/ner.12542
16. Narouze, S, Benzon, HT, Provenzano, D, et al. Interventional spine and pain procedures in patients on antiplatelet and anticoagulant medications (second edition): guidelines from the American Society of Regional Anesthesia and Pain Medicine, the European Society of Regional Anaesthesia and Pain Therapy, the American Academy of Pain Medicine, the International Neuromodulation Society, the North American Neuromodulation Society, and the World Institute of Pain. Reg Anesth Pain Med. 2018:43(3):225–262. https://doi.org/10.1097/AAP.0000000000000700
17. Petraglia FW 3rd, Farber SH, Gramer R, et al. The incidence of spinal cord injury in implantation of percutaneous and paddle electrodes for spinal cord stimulation. Neuromodulation. 2016;19(1):85–90. https://doi.org/10.1111/ner.12370
18. Deer TR, Lamer TJ, Pope JE, Falowski SM, et al. The Neurostimulation Appropriateness Consensus Committee (NACC) safety guidelines for the reduction of severe neurological injury. Neuromodulation. 2017;20(1):15–30. https://doi.org/10.1111/ner.12564
19. Falowski SM, Cecili A, Sestokas AK, et al. Awake vs. asleep placement of spinal cord stimulators: a cohort analysis of complications associated with placement. Neuromodulation. 2010;14(2):130–135. https://doi.org/10.1111/j.1525-1403.2010.00319.x