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Concerns on efficacy (particularly long term), safety and cost regarding Spinal Cord Stimulation (SCS). SCS involves the administration of electrical impulses in the spinal cord via an implanted device. SCS is considered a late or last alternative treatment for painful conditions such as chronic back and leg pain resulting from failed back surgeries, Complex Regional Pain Syndrome (CRPS) and chronic chest pain (angina). Important questions remain regarding the safety, efficacy, and cost-effectiveness of SCS.
Status: Review in progress
Spinal cord stimulation (SCS) was first reviewed by the HTA program in 2010.
All future dates are estimates and subject to change.
Chronic pain is a leading cause of disability and is an immense public health challenge. Pain is chronic when it occurs for extended periods (usually defined as >3 months), and can affect other aspects of an individual’s health and function, including physical, emotional, social, and mental, often leading to a loss in quality of life. Treatment of chronic pain aims to improve function and quality of life in addition to pain relief. Primary treatments include disease and injury-specific treatments such as nerve root decompression or reoperation, and other therapies such as pharmaceuticals, physical therapy, behavioral and psychological therapies, and neurostimulation therapies such as transcutaneous nerve electrical stimulation (TENS). Spinal cord stimulation (SCS) may be considered for moderate or severe pain that does not respond to standard therapies. A 2020 U.S. Food and Drug Administration (FDA) communication estimated that 50,000 SCS devices are implanted annually.
SCS was developed in the 1960’s based on the Melzack and Wall’s gate-control theory and has been used to treat a number of chronic pain issues. Mechanisms of pain relief using SCS are not completely understood, although current theories suggest stimulation occurs through a pulse delivering a specific current to dorsal fibers which interfere with or suppress the transmission of pain signals between nerves and the brain. Originally, pain relief through parameter changes were completely dependent on user input. Open loop and closed loop systems have been described. Open loop (OL) systems ignore external stimuli, such as movement of the spinal cord, heart rate, and respiration. In contrast, closed loop (CL) systems automatically adapt and modify stimulator settings in response to patient position and activity in real time, maintaining stimulation within an individualized therapeutic range. Further details on the mechanism of SCS systems have been described in great detail elsewhere.
SCS systems involve percutaneous implantation of electrode leads into the epidural space until they reach the dorsal column of the spinal cord. Currently, 16 FDA approved SCS devices are available. Approved musculoskeletal indications generally include Failed Back Surgery Syndrome (FBSS), Complex regional pain syndrome (CRPS) Types I and II, intractable low back pain and leg pain. Other indications include epidural fibrosis, degenerative disc disease, and arachnoiditis. Some SCS devices are approved for treatment of diabetic neuropathy. In 2016 the FDA gave premarket approval (PMA) to the first generation of devices implanted onto the dorsal root ganglion (DRG) of the posterior root to treat CRPS type I or type II, reflex sympathetic dystrophy, and causalgia. Compared with SCS devices, in which leads are implanted into the epidural space, DRG leads enter the epidural space, exit the neuroforamina, and stimulate the adjacent DRG, potentially providing more focused pain relief through specific targeting, as well as decreased paresthesia.
The pulse frequency used in SCS, measured in hertz (Hz), can be adjusted to meet the needs of individual pain thresholds. Traditional SCS systems are considered “low-frequency”, typically defined as 30 Hz to 200 Hz, but may be as low as 10 Hz or high as 1200 Hz.12 Low-frequency SCS is often associated with paresthesia, a feeling of tingling or buzzing that is perceived differently depending on the individual, which may or may not bring discomfort. “High frequency” (also referred to as “paresthesia free”) SCS systems, often defined as greater than 200 Hz, produce stimulations that are typically unperceivable by patients, and may be preferred.20 Currently, the highest frequency available is 10,000 Hz. Additionally, in 2016 the FDA approved a clinician application for SCS systems that provide stimulation in “bursts” rather than constant rates (referred to as tonic stimulation or burst stimulation), which may provide greater relief at lower frequencies.