FEATURE Spinal Cord Stimulation: Fundamentals Interventional pain specialists offer an overview of spinal cord stimulation (dorsal column neuromodulation) fun- damentals that referring physicians can use in clinical practice. Elmer G. Pinzon, MD, MPH Minimally Invasive Interventional Spine and Musculoskeletal Specialist President, Medical Director, Owner University Spine & Sports Specialists, PLLC Clinical Assistant Professor Department of Surgery Division of Surgical Rehabilitation University of Tennessee Graduate School of Medicine Knoxville, Tennessee James A. Killeffer, MD Assistant Professor Department of Surgery Division of Neurosurgery University of Tennessee Graduate School of Medicine Knoxville, Tennessee pinal cord stimulation (SCS) has been in visual analog pain scores, and improvement in activities used in pain management since C. of daily living. The hardware is more durable, more effec- Norman Shealy, MD, PhD, implanted tive, more maneuverable, and provides a greater range of the first neuroaugmentive device in a coverage for the affected area. The devices can be implanted cancer patient in 1967.1-3 Since then, sev- percutaneously under fluoroscopic guidance (especially for eral studies have examined the long-term the trial leads placement), which allows operator–patient S effects of SCS in pain management, with verbal interaction and more accurate positioning of spi- variable outcomes and success rates.4-8 As with many novel nal cord stimulator leads for trial and eventual permanent procedures, initial problems with SCS included poorly placement. In addition, more than three decades of expe- designed hardware, inadequate patient selection criteria, rience have provided improved patient selection criteria, and suboptimal surgical techniques.7,9-11 which is paramount in effecting a positive eventual out- Significant advances in SCS, however, have been made in come. The net result is an improved capability to control recent years. Postoperative outcomes of the procedures have various chronic pain conditions, especially those that are shifted to more positive outcomes in the field of neuroaug- peripherally referred as opposed to centrally referred.8 mentation, especially with respect to such practical factors This article will discuss the pathophysiology, mechanism as return to work, reduction in medication use, reduction of action, and clinical applications of SCS; as well as March 2013 | Practical Pain Management 27 Spinal Cord Stimulation: Fundamentals success of a spinal cord stimulator Table 1. Mechanistic Theories for SCS system.7,9-11 Technical advances lead- ing to improved hardware, coupled • Gate control theory—segmental, antidromic activation of A-ß efferents with improved patient selection, have • SCS blocks transmission in the spinothalamic tract improved the rate of long-term effi- • SCS produces supraspinal pain inhibition cacy of SCS to approximately 70% today, up from approximately 40% • SCS produces activation of central inhibitory mechanisms influencing sympathetic 3,4,8 efferent neurons since the 1970s and 1980s. A spinal cord stimulator neuro- • SCS activates putative neurotransmitters or neuromodulators modulation system should be consid- SCS, spinal cord stimulation ered for patients who have failed all reasonable conservative care includ- ing appropriate diagnostic, therapeu- current clinical results, and potential changes in blood flow and skin tem- tic, and rehabilitative techniques, and future trends in SCS, also known as perature from SCS may affect noci- have been given a reasonable period dorsal column neuromodulation. ception at the peripheral level.16-20 of time to recover from the condi- This postulation is further supported tion.8 A reasonable time period is at SCS Mechanism of Action in part by data from Marchand et al, least 6 to 12 months of conservative, Although the exact mechanism for who investigated the effects of SCS pain-relieving, minimally invasive pain control from SCS is not entirely on chronic pain using noxious ther- treatments, and/or failure of surgical understood, it is believed to result mal stimuli.21 Since it was discovered treatments, with persistent extremity from direct or facilitated inhibition of that SCS causes vasodilation in ani- pain greater than axial spine pain. pain transmission.3,5-7,12,13 Table 1 lists mal studies, clinicians have used this An ideal patient should be moti- the five mechanistic theories for why modality for the treatment of chronic vated, compliant, and free of drug SCS works.13 pain due to peripheral vascular disease dependence.33 Psychological screen- The gate control theory motivated and is the leading indication for SCS ing is recommended but not manda- Shealy et al to apply SCS as a means in Europe today.13,15,22-26 The precise tory to exclude conditions that predis- to antidromically activate the tactile action of pain modulation by SCS is pose to failure of the procedure (see myelinated A-β fibers through dorsal still in debate. A better understanding article on psychological evaluation in column stimulation.1,2 Shealy rea- of the pain system may lead to more SCS patients on page 35). Diagnoses soned that sustained stimulation of effective stimulators and allow for that are typical indications for this the dorsal columns would keep the even greater success. procedure include chronic radiculop- gate closed and provide continuous Today, the most common indica- athy, perineural fibrosis, neuropathic pain relief. While the theoretical “gate tion for SCS is for the treatment of pain, and complex regional pain control” model put forth by Melzack chronic low back and lower extrem- syndrome.34-38 In the United States, and Wall has been shown not to be ity pain due to chronic radiculopa- peripheral vascular disease is not an precisely correct, pain gating or pain thy or postlaminectomy lumbar pain FDA-approved indication. control has been shown to exist.5-7,12 syndrome despite adequate surgical When considering pain topogra- Others believe that pain relief from intervention.27-32 This population phy, extremity pain responds better SCS results from direct inhibition of represents the primary indication for than axial pain, and the more distal pain pathways in the spinothalamic SCS in our practice and has provided the extremity pain the greater the tracts and not secondary to selective us with an effective treatment option. clinical response.27,39 Middle and large fiber stimulation.14 This theory Table 2 contains a list of commonly upper lumbar pain as well as tho- has been supported by Hoppenstein, accepted and potential indications, racic, cervical, and chest wall pain who showed that the posterolateral in addition to commonly accepted are difficult to adequately control stimulation of the spinal cord pro- contraindications. and maintain long term. Pain due to vided effective contralateral pain relief severe nerve damage superimposed on with substantially less current than Selection Criteria cutaneous numbness (ie, anesthesia posterior stimulation.15 As noted, proper patient selec- dolorosa) is also difficult to treat with Some investigators think that the tion is essential to the long-term SCS. Central pain syndromes do not 28 Practical Pain Management | March 2013 Spinal Cord Stimulation: Fundamentals Table 2. SCS Indications and Contraindications Commonly accepted indications • Chronic pelvic pain • Postherpetic neuralgia • Deafferentation pain • Intercostal neuralgia • Axial pain • Post-laminectomy (thoracic region) syndrome (ie, FBSS) • Thoracoabdominal aortic aneurysm • Post-laminectomy (lumbar region) syndrome (ie, FBSS) • Cerebral palsy • Cauda equina (chronic) injury syndrome • Multiple sclerosis • Chronic arachnoiditis • Spinal cord injury • CRPS of the upper limb Commonly accepted contraindications (Absolute) • CRPS of the lower limb • Sepsis • CRPS of other specified site • Coagulopathy • Phantom limb pain syndrome • Previous surgery or trauma that obliterates the spinal • Cardiovascular angina/ischemic pain canal • Atherosclerosis of the extremities with resting pain • Localized infection at the implantation site (ie, peripheral vascular disease) • Spina bifida • Brachial neuritis or chronic cervical radiculopathy Commonly accepted contraindications (Relative) • Thoracic or lumbosacral neuritis or chronic • Physical and/or cognitive/psychological disability that radiculopathy interferes with proper usage of and understanding of • Cervical nerve root injury the device • Thoracic nerve root injury • Significant somatization/somatoform disorders • Lumbar nerve root injury • Unmanaged substance abuse or cognitive disorders Other potential indications • Lack of social support • Chronic occipital neuralgia/cervicalgia CRPS, complex regional pain syndrome; FBSS, failed back surgery syndrome; SCS, spinal cord stimulation respond to SCS and are best treated healthcare system. leads are sutured tightly with anchors by other modalities. The process of the trial percutane- to the skin. Subsequently, the com- ous spinal cord stimulator approach pleted circuits are taped securely to Percutaneous Trial should involve an alert and communi- the skin and covered to prevent them The use of an outpatient percutane- cative patient who can provide the from accidently being pulled out but ous trial of between 3 to 7 days with practitioner with correct lead posi- still allow them to be attached to the an SCS system has been proven help- tioning. The patient should be made programmer. Then, to verify the final ful in determining which patients