Chronic pain, particularly neuropathic pain, is rarely treated adequately by pharmacotherapy. Spinal cord stimulation (SCS) therapy, which was introduced more than 50 years ago, is delivered by a neurostimulator implanted under the skin. It works by disrupting the pain signals traveling between the spinal cord and brain. Recent developments in SCS technology offer nonpharmacologic treatment options for patients with intractable chronic pain conditions that act not only on physical pain symptoms but also on the emotional effects of chronic pain.
The gate-control theory of pain proposed by Melzack and Wall in 1965 spurred the development of conventional, or tonic, SCS. Devices were first implanted in 1967 by Shealy, who noted that paresthesia elicited by electrical stimulation of the dorsal columns (DC) inhibited deep pain due to metastatic lung cancer.
However, tonic SCS frequently leaves patients with insufficient pain relief and uncomfortable paresthesias (described as an abnormal tingling or pricking sensation), leading manufacturers to develop new stimulation waveforms including burst and high frequency. Whereas tonic stimulation relies on the clinician’s ability to successfully overlap stimulation-induced paresthesias with chronically painful areas, the new waveforms have improved clinical outcomes and are reported to provide a more comfortable patient experience.
Tonic SCS mainly acts via a segmental spinal mechanism where it induces the release of GABA from inhibitory interneurons in the spinal dorsal horn. Tonic SCS concurrently initiates modulation of neuropathic pain through a supraspinal-spinal feedback loop and serotonergic descending fibers. Activation of pain fibers also induces tingling paresthesias in the dermatomal regions correlated with the area of the spinal cord where the stimulation is applied, which clinicians find useful to map the extent of the stimulation, but which are also often uncomfortable for patients. In addition, pain relief – generally accepted as 50% in approximately half of patients – may be insufficient and decrease over time, resulting in continued opioid use for some.
High frequency SCS using 10 kHz frequency (HF 10 therapy) requires less rigorous placement of leads and has been shown to produce pain control without paresthesias. Research has shown that patients prefer the higher frequency approach over tonic SCS, and in the SENZA trial, 84.5% of patients implanted with HF 10 therapy experienced a 50% or greater reduction in back pain and 83.1% experienced a reduction in leg pain after three months of treatment. Among those receiving traditional SCS, 43.8% experienced a reduction in back pain and 55.5% had reduced leg pain. These results were sustained through 24 months of treatment.
Burst SCS was introduced in 2010 and was shown to result in statistically superior pain relief compared with tonic stimulation in SUNBURST, a large prospective, randomized, controlled clinical trial. In this study, using a multimodal stimulation device, burst stimulation was found to be noninferior (P< 0.001) and also superior (P < 0.017) to tonic stimulation for the treatment of chronic pain of the trunk and/or limbs. Among 100 participants, 70.8% initially preferred burst stimulation over tonic stimulation. After one year, 68.2% of subjects preferred burst stimulation, which was found to be effective and safe.
Burst stimulation is a novel waveform made up of closely spaced, high-frequency electrical impulses delivered in packets, which are followed by a quiescent period or interburst interval. It acts to suppress pain in the target region below the patient’s perception threshold, resulting in less paresthesia and greater patient comfort. With burst stimulation, the impulses traveling to the thalamus target both the lateral area, which controls the individual’s perception of pain, and the medial area, which controls the emotional response and attention to painful stimuli. Tonic stimulation engages only the lateral pathway.
Compared to traditional neurostimulation therapy, burst stimulation has been shown to provide superior relief from pain and its associated suffering. It also improves patients’ ability to perform everyday activities and can reduce the paresthesia felt with traditional neurostimulation.
“’Chronic pain’ is a broad term that doesn’t accurately capture the variety of issues and symptoms people experience as a result of it,” said Timothy Deer MD, DABPM, president and CEO of The Spine and Nerve Center of the Virginias in Charleston, West Virginia.
In the recent BurstDR micrOdosing StimuLation in De-novo patients (BOLD) study presented at the 2020 North American Neuromodulation Society annual meeting, the Proclaim XR neurostimulator (Abbott) was found to reduce pain catastrophizing scale scores by an average of 62%, as assessed on a patient reported measure used to determine how pain affects mental state.
In addition, at baseline 78% of patients had an Oswestry Disability Index (ODI) score of “severe,” “crippling,” or “bed bound.” After six months of treatment, 71% of patients had a minimal or moderate ODI score, and 29% had a “severe” or crippling score.
Corey Hunter, MD, founder of the Ainsworth Institute of Pain Management in New York City, noted that after 90 days with a burst device, patients reported that their pain might still be rated as a 2 or 3, but their emotional state improved to the point that they no longer felt the anxiety associated with the pain. “Patients using the devices say the pain no longer scares them or they’re no longer afraid of going out and having, say, a panic attack. When you see this happening in your patients, you can’t deny the benefits.”
Spinal cord stimulation is indicated as a treatment option for multiple chronic neuropathic pain syndromes. It is generally offered to patients whose previous treatments have failed, such as physical therapy, oral or transdermal medications, injections or radiofrequency, or surgery. SCS is also indicated for the treatment of complex regional pain syndrome (CRPS) and diabetic neuropathy. The patient selection process involves psychological screening and a trial of the device before it is implanted.
When asked if he had a preference in SCS devices Dr. Hunter told PPM, “I’m still on the fence as to which device I prefer in my practice. Many patients still need opioids on tonic stimulation devices. The costs of the devices are equivalent, but the burst pulses are energy efficient, so a battery can last for up to 10 years.”