The use of spinal cord stimulation (SCS) has become an essential part of the treatment algorithm for neuropathic pain states, and is considered standard of care for various pain conditions refractory to conservative management. Since the inception of the technology, there has been incremental improvement in the design of the hardware, such as more complex electrode configurations, battery design and recharge capability and imaging compatibility. More recently, there has been substantial advancement in the delivery of electrical energy via novel waveforms and the identification of different neural substrates and targets. Importantly, we have seen some of the most significant improvements in patient response and outcomes with the transition from primarily tonic/paresthesia-based to subthreshold/paresthesia-free stimulation.
History and Technology
The first use of SCS was reported by Dr. Norman Shealy in 1967 via high thoracic laminectomy for intradural implantation of a vitallium electrode in a patient with cancer-related pain. This provided proof-of-concept for “dorsal column stimulation” based on the concept of gate control by Melzack and Wall. This initial success led to the development of the first commercially-implantable stimulator in 1968, which used platinum electrodes and required an external power supply. Much of the early SCS technology was based on systems designed for cardiac stimulation. Throughout the next decade, the technical components of SCS saw significant refinement, such as the introduction of percutaneous implantation techniques in 1975, before the first fully-implantable system was introduced in 1981. The US Food and Drug Administration (FDA) then approved SCS in 1989 for the treatment of chronic pain from nerve damage in the trunk, arms or legs.
As SCS technology evolved, so did the indications and criteria for implantation. Initially, SCS was used to treat a variety of pain syndromes, although with mixed results. Neuropathic pain pathologies, or those associated with nerve damage, have typically been considered the most responsive to SCS, with the most common location of chronic neuropathic pain being in the back and legs.
Evidence and Indications
Of patients undergoing lumbosacral spine surgery for a surgically identifiable pathology, 10-40% will experience persistent or recurrent pain. Traditionally, this was referred to as failed back surgery syndrome or post-laminectomy syndrome; however, due to misleading and inadequate labeling, the term “persistent spinal pain syndrome” (PSPS) has instead been proposed. A paradigm shift for SCS as a therapy came with the publication of the randomized controlled study by North et al., reporting SCS as more effective than reoperation in the treatment of persistent pain after lumbosacral spine surgery. These results were further strengthened with the publication of the Prospective, Randomized, Controlled, Multicenter Study of Patients with Failed Back Surgery Syndrome (PROCESS) study by Kumar et al., reporting significantly improved pain relief, quality of life and functional capacity with SCS compared to conventional medical management (CMM).
SCS has a robust evidence base, with multiple randomized controlled trials providing Level I Evidence in support of different clinical indications. For example, the superiority of SCS compared to CMM has been demonstrated in the treatment of complex regional pain syndrome type I and painful diabetic neuropathy. Technological innovation is just as important as expanding clinical indications, with high quality data generated from randomized controlled trials evaluating high frequency stimulation (SENZA), burst stimulation (SUNBURST), evoked compound action potentials (EVOKE) and differential target multiplexed stimulation, to name a few. These studies have been both physician and industry-run, and many are a collaborative effort between surgeons and pain physicians. Importantly, despite the high upfront costs of SCS, the therapy has reported to be cost-effective over the long-term in the treatment of PSPS, complex regional pain syndrome and painful diabetic neuropathy.
Non-Surgical Low Back Pain
Low back pain is a highly prevalent musculoskeletal problem, with nearly 35 million American adults experiencing chronic pain refractory to conservative care. A particular challenge with SCS has traditionally been relieving low back pain as opposed to radicular pain — predominant axial pain has been reported as an unfavorable prognostic factor following both revision spine surgery and conventional SCS. This was in part attributable due to the difficulty achieving an overlap of paresthesias in the low back area. The publication of the SENZA randomized controlled trial in 2015 changed the landscape of SCS, demonstrating that high-frequency, paresthesia-free therapy was superior to traditional, paresthesia-based SCS in the treatment of low back and leg pain.
Although much of the SCS research focus has been on patients with persistent post-surgical pain, a significant proportion of people living with low back pain are not appropriate candidates for spinal surgery. So-called non-surgical back pain (NSBP) describes patients with refractory pain due to degenerative disc disease, facet disease and/or spinal stenosis, often with multiple pain generators, but without a surgically correctable pathology. These patients often undergo repeated cycles of physical therapy and injections in combination with oral medications — the role of neuromodulation has been unclear, particularly in those patients who develop chronic pain refractory to other therapies.
Recently, the Dorsal Spinal Cord Stimulation vs Medical Management for the Treatment of Low Back Pain (DISTINCT) study was published, demonstrating the superiority of SCS compared to CMM on measures of pain and function, with reduced utilization of subsequent interventional procedures and opioid use. This study paved the way for a new FDA indication for SCS, with further Level I Evidence and support from additional randomized controlled trials.
A Multidisciplinary Approach
As innovation in medical device technologies has expanded the indications for treatment, so has the role of the neurosurgeon. This has also led to significant treatment overlap with other physicians, particularly pain practitioners. Pain conditions are diverse and complex, with a variety of treatment options available; as such, this has expanded the dialogue between specialties and promoted communication and collaboration. A collaborative approach to the treatment of chronic pain is necessary, including the judicious use of oral opioids in conjunction with other medications, psychological counseling, physical therapy, interventional procedures and possibly surgery. Equally important is ensuring open communication between multidisciplinary team members and patients.
It is important to recognize that the goal of SCS, and of all pain therapies, is not to eliminate pain, but to improve quality of life. Ultimately, having open communication within the multidisciplinary team is equally as important as building trust between patients and their providers.
Conclusion
As SCS technology and indications continue to evolve, we will see more effective and potentially more personalized pain control. It is important that the neuromodulation field continues to grow through collaboration between physicians, scientists and industry, always with the goal of improving quality of life for the patient.
Steven M. Falowski, MD, FAANS, is a functional neurosurgeon out of Lancaster, Penn. He is president of the AANS/CNS Executive Pain Committee, vice president of the American Society Pain and Neuroscience, president elect of the Pennsylvania Pain Society, on the Board of Directors for the International Neuromodulation Society, senior advisor and meeting chair of the North American Neuromodulation Society and the senior advisor of the Board of Directors for the Pacific Spine and Pain Society.
Michael D. Staudt, MD, FAANS, is an associate professor of neurosurgery at UH Cleveland Medical Center and Case Western Reserve University School of Medicine, where he is the director of epilepsy surgery and the co-director of pain surgery and neuromodulation. He holds the George R. and Constance P. Lincoln Endowed Chair in Brain Health. He serves as a director-at-large for the North American Neuromodulation Society, a member-at-large on the AANS/CNS Joint Section on Pain and is the Pain Section Guideline chair for the AANS/CNS Joint Guidelines Review Committee.
