Spinal Cord Stimulation (SCS) is a treatment for chronic pain that uses a small implanted device to deliver mild electrical pulses to the spinal cord. This electrical energy interrupts or modifies pain signals before they reach the brain. Historically, this therapy relied on generating a tingling sensation, known as paresthesia, to mask the pain. Today, neuromodulation is moving beyond this traditional approach, focusing on sophisticated electrical signals and hardware for greater patient comfort and long-term efficacy. This evolution involves changes to energy delivery, system adaptation, and the physical characteristics of the implanted device.
Advancements in Stimulation Patterns
New stimulation patterns shift how SCS treats pain, often moving away from the paresthesia-based tingling sensation of older systems. These newer methods deliver electrical signals below the patient’s perception threshold, achieving pain relief without the feeling of electricity. High-Frequency (HF) stimulation, for instance, uses a rate of 10,000 Hertz (Hz), which is faster than the 40–100 Hz used in traditional tonic stimulation. This higher frequency is thought to affect different nerve fibers and pain pathways compared to conventional systems.
Burst stimulation mimics natural nerve firing patterns, delivering short, high-rate packets of electrical pulses followed by silence. This method provides pain relief and often addresses the emotional aspect of chronic pain without paresthesia. Differential Target Multiplexed (DTM) stimulation is a complex waveform using multiple electrical signals simultaneously. Preclinical research suggests the DTM waveform may uniquely modulate the interaction between neurons and glial cells in the spinal cord, which play a role in chronic pain.
These non-traditional patterns allow clinicians to offer personalized therapy, especially for patients not adequately addressed by older tonic stimulation. The availability of multiple waveforms in a single device provides options for patients whose pain evolves or who experience a decrease in effectiveness with one pattern. Achieving pain relief without constant paresthesia improves quality of life for many patients.
Closed-Loop and Adaptive SCS Systems
The most advanced operational change in spinal cord stimulation is the introduction of closed-loop, or adaptive, systems. Traditional SCS devices are open-loop, delivering fixed stimulation regardless of the patient’s position or activity, which can cause uncomfortable over-stimulation or ineffective under-stimulation. Closed-loop systems overcome this by actively monitoring the spinal cord’s response to electrical pulses in real-time.
These systems measure the Evoked Compound Action Potential (ECAP), the electrical signal generated by the spinal cord in response to the delivered stimulation. By continuously sensing the ECAP, the device uses this information as feedback to automatically adjust the stimulation amplitude. This dynamic adjustment ensures the therapy remains within an optimal therapeutic window, maintaining consistent pain relief even when the patient changes posture, such as standing up or bending over.
This adaptive technology aims to provide stable pain management, minimizing the need for manual adjustments. Clinical evidence, such as the Evoke study results, shows that closed-loop systems provide greater pain relief and fewer instances of uncomfortable over-stimulation compared to open-loop systems. This real-time feedback mechanism allows the system to interact with the nervous system in a new way.
Miniaturization and Implant Longevity
Hardware advancements have made implanted SCS components smaller and more convenient. Modern Implantable Pulse Generators (IPGs), which house the battery and electronics, are designed with smaller profiles, reducing the surgical footprint and increasing patient comfort. For instance, some of the smallest rechargeable IPGs have volumes around 13.6 to 13.77 cubic centimeters.
Battery technology has progressed, focusing on reducing the burden of recharging for the patient. While some SCS systems use primary cell (non-rechargeable) batteries with a median lifespan projected around 8.2 years, rechargeable systems extend the time between charging sessions. Certain new rechargeable systems utilize low-energy technology to reduce the required charging frequency to as few as five times per year under normal use, improving upon older models that required daily or weekly charging.
Compatibility with diagnostic imaging is another hardware improvement. Many modern SCS systems are now conditionally approved for full-body Magnetic Resonance Imaging (MRI) scans at both 1.5T and 3T. This is a key consideration for patients who may require MRI diagnostics, as compatibility ensures the device does not interfere with necessary imaging technology.
The Patient Experience and Clinical Process
SCS therapy begins with a thorough screening to determine candidacy, typically including a psychological evaluation and a review of previous pain treatments. The regulatory process mandates a temporary trial period, acting as a “test drive” before permanent implantation. This trial usually lasts five to seven days and involves temporary placement of leads in the epidural space, connected to an external generator worn on a belt.
During the trial period, patients are encouraged to try activities that their chronic pain previously prevented them from doing, while following specific restrictions like avoiding bending, twisting, or lifting heavy objects. The trial is considered successful if the patient experiences a reduction in pain, typically defined as 50% or more, along with improved function and quality of life. The newest stimulation patterns and adaptive systems are often used during this trial to demonstrate the potential for paresthesia-free relief and consistent comfort.
If the trial is successful, the patient proceeds to the permanent implantation of the IPG, which is placed beneath the skin. Long-term management involves routine follow-up visits where the device programming is optimized, utilizing the multiple waveforms and adaptive features now available. These advanced systems provide clinicians with more data and flexibility, allowing them to continually personalize the therapy as the patient’s pain condition changes over time.