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Complications of Spinal Cord Stimulation
Introduction
The use of neurostimulation to change the perception of pain and modulate neural responses has become an important part of the pain treatment continuum. Advocates herald neurostimulation as an important part of this continuum for intractable neuropathic and mixed-pain syndromes. Recent level-one studies have supported this optimistic view, but adverse events subsequent to this therapy must be recognized, addressed, and mitigated when possible. This chapter highlights the characteristics and possibilities of complications and addresses potential solutions for improving practice and mitigating adverse events.
Background
Rising healthcare costs are of significant concern among policymakers. Complications are particularly important, and have been subject to quality reporting measures and changes in reimbursement ( ). Spinal cord stimulation (SCS) is a superior cost-effective treatment for specific patient populations ( ) despite moderate to high initial costs ( ). Unexpected or excessive complications can threaten the longevity and cost effectiveness of this therapy. Uncomplicated maintenance of implanted systems is a low-cost medical intervention even accounting for implantable pulse generator (IPG)/battery replacement. However, postoperative complications are associated with a threefold increase in the annual expense and pose a threat to the therapy ( ).
Overview of Complications
Complications of SCS can be divided into three broad categories: technical issues, biological causes ( ), and tolerance to the therapy ( ). Until the early 2000s complications data was sparse and limited to statistically inferior case studies, case series, and literature reviews ( ). Systematic reviews of SCS in the treatment of failed back surgery syndrome (FBSS) and complex regional pain syndrome (CRPS) focused on predictability of outcomes and satisfaction, perioperative and postoperative complications, or both ( ).
Prospective randomized controlled studies with long-term follow-up have provided detailed data on the efficacy and complications of SCS. randomized 36 patients with CRPS of the upper or lower extremities into two groups: those receiving physical therapy alone, and those receiving both SCS and physical therapy. Of the 36 trialed patients, 24 received permanent implantation (trial to permanent implant ratio of 67%); the study reported a 25% complication rate at 6 months, encompassing 11 different complications. The most common complication was dural puncture during the trial phase, which occurred in four of 36 patients, with two patients developing postdural puncture headache. Following implantation, the occurrence of reoperation was most frequently due to electrode displacement or IPG pocket pain. Furthermore, this study reported a 100% “side-effect” rate by 2 years, including painful positional paresthesia, undesired paresthesia in other body parts, and pain from implanted hardware ( ). In a 5-year follow-up, analyzed the cohort of patients and noted that complications had declined somewhere in between the third and fifth years after implantation. Thus 72% of complications most often occurred in the first 2 years after implant when compared to the 5% of complications thereafter. Reoperation was related to lead repositioning or replacement, IPG pocket revision, or IPG replacement ( ).
Another prospective randomized controlled study reviewed the effectiveness and complications of 100 patients with FBSS in 12 centers when comparing SCS to medical management ( ). During the first 12 months of the study, 32% of the SCS group experienced 40 device-related complications, resulting in a 24% reoperation rate. Hardware complications were mainly attributed to lead migration, fracture, or generator migration. There was a 19% biologic complication rate, 8% of which was related to infection or wound breakdown. Although hardware complications were lower than previously reported, there was a higher infection rate. Seeding of bacteria during the trial phase was suspected, and most likely had not been previously reported ( ).
Consistent with previous CRPS studies ( ), reported a significant reduction in the rate of complications after 12 months, although by 24 months 45% of the patients experienced at least one complication. Of the cases requiring revision, 79% occurred within the first 12 months ( ). The most common complications were electrode migration, loss of paresthesia, and pain at the site of the IPG.
At least two comprehensive retrospective reviews were published in 2004 that examined the efficacy and safety of SCS for the treatment of FBSS, CRPS, and other painful chronic conditions ( ). assessed 583 studies, classified as Class I, II, or III studies from 1990 until 2003, and considered 22 articles for analysis of complications. Most patient complaints that resulted in removal of the device resulted from pain at the generator site. Considering the data in 18 articles, there was an overall weighted complication rate of 34.3%, ranging from none to 81%. Superficial infections accounted for only 4.5% and deep infection accounted for 0.1% of the complications. The most common adverse event resulting in revision was lead-related repositioning (23.1%). Overall there was a 10% equipment failure rate. Turner et al. concluded that life-threatening complications of SCS therapy are rare, and complications that lead to device revision are common and increase incrementally from the time of implant. Furthermore, this literature review could not accurately determine whether SCS therapy loses efficacy over time, a finding consistent with other studies ( ).
performed a 20-year literature review, evaluating the safety and efficacy of SCS for the treatment of chronic back and leg pain, CRPS 1 and CRPS 2, ischemic limb pain, angina, and various other diagnoses that include peripheral neuropathy, plexopathy, phantom limb pain, and arachnoiditis. Fifty-one papers covering 2972 patients met the inclusion criteria of the review. Biological complications (infection, epidural hemorrhage, seroma, hematoma, paralysis, cerebral spinal fluid leak, and skin erosion) and hardware complications (lead migration, overstimulation or understimulation, intermittent stimulation, pain over the implant site, lead breakage and migration, hardware malfunction, and loose connections) were considered. Consistent with other reviews ( ), most complications were not life threatening. Hardware-related complications were most frequent, with lead migration accounting for 13.2% of all complications, while lead breakage and hardware malfunction accounted for 9.1% and 2.9%, respectively. Reoperation rates for lead migration were reduced significantly when multipolar leads replaced monopolar leads, consistent with other studies ( ). IPG/battery failure accounted for 1.6% of the complications, but most of these failures did not occur before 3 years, which was within the accepted battery life expectancy. Biologic complications were much less likely, and data mined from the literature reveals a biologic complication rate of 3.4%. Most of these biologic complications were superficial infections and resolved with antibiotics, explantation, or both ( ).
More recent reviews corroborate this complication data ( ). performed a retrospective analysis of 707 consecutive cases where SCS therapy was used for the treatment of FBSS, CRPS, peripheral vascular disease, visceral pain, and peripheral neuropathy. The authors reported no permanent neurological deficits or deaths in their analysis. Consistent with previous studies ( ), hardware complications were most prominent: 22% of these cases were related to lead migration, 9.5% to lead connection failure, and 6% to lead breakage. Similarly, in another retrospective analysis Hayek et al. found hardware-related issues to be pervasive, representing 74.6% of all complications ( ). The overall infection rate was 4.5%, and 22 of 32 cases (68.7%) of infection were noted to be deep infections ( ). Eighteen of the 22 cases of deep infections were associated with abscess formation, with one case of epidural abscess. The authors noted a nonstatistically significant 9% infection rate in diabetics when compared to the 4% of patients with no known diabetes. Methicillin-resistant Staphylococcus aureus (MRSA) was implicated in 15% of all infections. Of particular note, the study found that there was a higher incidence of infection among patients with FBSS (6.3%) when compared to the cohort average of 4.5% ( ). Although not statistically significant, the authors postulated that delayed or undiagnosed infection following back surgery could transfer an increased risk to the SCS implant.
Identification and Management of Complications
Patient Selection
The most prudent physician will use good clinical judgment and critical analysis to anticipate and minimize perioperative and postoperative complications. Patient selection is of utmost importance, and multiple factors must be taken into account. Indications for the procedure should correlate with those diagnoses known to respond to SCS ( ).
Candidates for SCS therapy should be rigorously screened. Demographics such as age, sex, and number of previous operations were not shown to anticipate complications ( ), although one retrospective review reported that youth, male gender, high pain intensity, and associated musculoskeletal complaints had a higher revision rate when compared to other demographics ( ). Patients who are not candidates for SCS therapy are those with known uncorrectable coagulopathy or those unable to stop anticoagulant or antiplatelet therapy. Similarly, patients with active infections (including urinary and dental infections) or sepsis should not be considered for SCS trial or implantation. Other known risk factors such as uncontrolled diabetes, tobacco abuse, immune deficiency or ongoing immunosuppressive therapy, and poorly compensated cognitive impairment must be considered ( ).
The use of SCS to treat angina and heart failure in both clinical practice and research settings has changed the thought processes regarding the concomitant use of SCS with implanted cardiac devices such as pacemakers and defibrillators. In recent years there have been reports suggesting problematic interference interactions between cardiac devices and SCS devices ( ). More data is needed to quantify the risks of SCS and automatic implantable cardioverter-defibrillator (AICD) interactions. The use of SCS in patients with an implanted AICD device should be based on a careful discussion of risks, postoperative monitoring, care team assessment, and the relative contraindications ( ).
Clearance should be obtained from the cardiac care team when contemplating SCS placement in a patient with an implanted cardiac device. During the trial and in the postimplant period the device should be interrogated and the patient monitored.
Although the use of SCS in pregnancy is not sanctioned by device companies and is listed as a contraindication in the “Directions for Use” manuals, available data regarding its use in pregnancy is mostly limited to case reports that demonstrate no adverse effects on pregnancy outcomes ( ).
Preoperative radiological assessment should be used to improve safety of SCS and reduce risks to the patient. Patients who present with potential structural anomalies, such as spinal stenosis, should have preoperative radiographs and magnetic resonance imaging (MRI) or computed tomography (CT) examination of the cervical, thoracic, and/or lumbar spine, based on the planned implant site, in anticipation of difficulties in lead placement ( ). In patients with anomalies that narrow the spinal canal, such as thoracic or cervical spinal stenosis, lead placements can result in neurologic sequelae such as hemiparesis, hemiplegia, quadriparesis, and quadriplegia.
Psychiatric comorbidities may negatively affect outcomes of SCS therapy. While psychological screening by a licensed practitioner can identify psychiatric comorbidities that may be a contraindication for SCS, it is also useful for setting realistic expectations of the therapy between the patient and the physician. Although untreated or poorly treated psychiatric disease may pose a barrier to successful SCS therapy in some cases, there are recent studies suggesting that this patient profile may benefit from novel waveform technologies ( ). Please see Chapter 2 by Doleys in this book.
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