Definition and Overview
Spinal cord stimulation (SCS) is an implantable neuromodulation therapy that delivers electrical stimulation to the dorsal columns of the spinal cord through electrodes placed in the epidural space, thereby modulating the transmission of chronic pain signals. Since it was first performed by Shealy et al. in 1967, over half a century of clinical experience has been accumulated.
More than 50,000 SCS procedures are performed worldwide annually, establishing it as a major treatment option for medication-refractory chronic neuropathic pain [3].
Principles and Mechanisms
Gate Control Theory
The classical mechanism of SCS is based on the gate control theory of Melzack and Wall. Electrical activation of large myelinated fibers (A-beta fibers) in the dorsal columns inhibits the transmission of pain signals carried by thin unmyelinated fibers (C fibers) at the dorsal horn of the spinal cord.
Modern Mechanisms
Recent research has revealed multilayered mechanisms including enhanced GABA release, inhibition of excitatory amino acids, activation of serotonergic and noradrenergic systems, and modulation of supraspinal pathways. High-frequency (10 kHz) stimulation and burst stimulation are thought to involve additional mechanisms that cannot be explained by gate control theory alone [4].
Indications
The major indications recognized by international guidelines are as follows [3].
- Failed back surgery syndrome (FBSS): the most common indication
- Complex regional pain syndrome (CRPS): Type I and Type II
- Diabetic peripheral neuropathy: efficacy recently demonstrated in randomized controlled trials [5]
- Ischemic pain due to peripheral vascular disease
- Refractory angina
Procedure Process
Trial Stimulation Phase
Under local anesthesia and fluoroscopic guidance, percutaneous electrodes are inserted into the epidural space. Electrodes are positioned at the spinal level corresponding to the pain region, and trial stimulation is performed with an external stimulator for 7–14 days. A pain diary is maintained during this period to evaluate efficacy.
Permanent Implantation
If the trial stimulation demonstrates 50% or greater pain reduction and functional improvement, a permanent system is implanted. Either percutaneous cylindrical or surgical paddle electrodes are used, and the implantable pulse generator (IPG) is placed subcutaneously in the abdomen or buttock.
Programming
Stimulation parameters (frequency, pulse width, current intensity, active contacts) are optimized to match the patient's pain pattern and activity level. Patients can adjust stimulation intensity with an external remote control or switch between preset programs.
Treatment Efficacy
FBSS
In the PROCESS trial, 48% of patients in the SCS plus conservative treatment group achieved 50% or greater leg pain reduction, compared with only 9% in the conservative treatment alone group [2]. The effect was sustained at 24-month follow-up.
CRPS
In a randomized controlled trial, the Visual Analog Scale (VAS) scores in the SCS group were significantly reduced compared with the control group, and the effect persisted at 5-year follow-up [1].
Diabetic Neuropathy
Fifty-nine percent of patients in the SCS group achieved 50% or greater pain reduction, compared with only 7% in the optimal medical therapy group [5].
Advances in Stimulation Modalities
Conventional Tonic Stimulation
Low-frequency stimulation at 40–60 Hz produces paresthesia (tingling) in the painful area to replace the sensation of pain.
High-Frequency Stimulation (HF10)
High-frequency stimulation at 10 kHz provides pain relief without paresthesia. Randomized controlled trials have demonstrated superior efficacy compared with conventional low-frequency stimulation for both back and leg pain [4].
Burst Stimulation
Burst-pattern stimulation has been reported to modulate the medial pain pathway, improving not only pain intensity but also its emotional component.
Closed-Loop Stimulation
This state-of-the-art technology measures evoked compound action potentials (ECAPs) in real time to automatically adjust stimulation intensity.
Side Effects and Complications
- Lead migration: occurs in approximately 10–15% of cases and may require revision surgery.
- Infection: approximately 3–5%, primarily at the IPG pocket site
- Post-dural puncture headache: approximately 1%
- Hardware malfunction: extension wire breakage, battery depletion
- Uncomfortable paresthesia: reported by some patients with conventional low-frequency stimulation.