Definition and Overview
Spinal cord stimulation (SCS) is an implantable neuromodulation treatment that modulates the transmission of chronic pain signals by delivering electrical stimulation to the posterior column of the spinal cord through electrodes placed in the epidural space. Since it was first implemented by Shealy et al. in 1967, more than half a century of clinical experience has been accumulated.
More than 50,000 SCS cases are performed annually worldwide, and it has become a major treatment option for drug-refractory chronic neuropathic pain.
Principle and mechanism
gate control theory
The classical mechanism of SCS is based on the gate control theory of Melzack and Wall. Electrically activating the thick myelinated nerves (Aβ fibers) in the posterior column inhibits the transmission of thin unmyelinated nerve fibers (C fibers) that transmit pain signals in the dorsal horn of the spinal cord.
modern mechanism
Recent studies have revealed multi-layered mechanisms such as promoting GABA secretion, suppressing excitatory amino acids, activating the serotonin and norepinephrine systems, and regulating the supraspinal pathway. High-frequency (10 kHz) stimulation and burst stimulation are presumed to have additional mechanisms that cannot be explained by the existing gate theory alone.
Indications
The main indications recognized by international guidelines are as follows.
- Failed back surgery syndrome (FBSS): the most common indication
- Complex Regional Pain Syndrome (CRPS): Type I and Type II
- Diabetic Peripheral Neuropathy: Effectiveness Proven in Recent Randomized Controlled Trials
- Ischemic pain due to peripheral vascular disease
- Refractory angina
Procedure
test stimulus phase
A percutaneous electrode is inserted into the epidural space under local anesthesia and under fluoroscopic guidance. Electrodes are placed at the spinal cord level corresponding to the painful area, and test stimulation is performed with an external stimulator for 7 to 14 days. During this period, a pain diary is recorded to evaluate the effectiveness.
permanent implant
If pain reduction and functional improvement of more than 50% are confirmed in the test stimulation, a permanent system is implanted. The electrodes are percutaneous cylindrical or surgical paddle type, and the stimulation generator (IPG) is implanted subcutaneously in the abdomen or buttocks.
programming
Optimize stimulation conditions (frequency, pulse width, current intensity, active contact point) according to the patient's pain pattern and activity pattern. Patients can adjust stimulation intensity or switch between preset programs using an external remote control.
treatment effect
FBSS
In the PROCESS study, 48% of the SCS + conservative treatment group achieved a 50% or greater reduction in lower extremity pain, compared to only 9% of the conservative treatment alone group. The effect was maintained even at 24-month follow-up.
CRPS
In a randomized controlled trial, the visual pain scale (VAS) of the SCS group significantly decreased compared to the control group, and the effect persisted even at 5-year follow-up.
diabetic neuropathy
While 59% of the SCS group showed a pain reduction of more than 50%, only 7% of the optimal drug treatment group showed a pain reduction of more than 50%.
Evolution of stimulation methods
Conventional method (Tonic stimulation)
This method replaces pain by causing abnormal sensations (tingling, paresthesia) in the painful area through low-frequency stimulation of 40 to 60 Hz.
High frequency stimulation (HF10)
10 kHz high-frequency stimulation controls pain without abnormal sensations. In a randomized controlled trial, it was shown to be superior to the existing low-frequency method for both back pain and lower extremity pain.
Burst stimulation
It has been reported that high-frequency burst pattern stimulation modulates the inner pain pathway and even improves the emotional component of pain.
Closed-loop stimulation
It is the latest technology to automatically adjust stimulation intensity by measuring spinal cord evoked compound action potential (ECAP) in real time.
Side effects and complications
- Electrode migration: Occurs in approximately 10-15% of cases and may require a repositioning procedure.
- Infection: Approximately 3-5%, mainly in the IPG pocket area.
- Headache after dural puncture: approximately 1%
- Device failure: broken extension cord, dead battery
- Discomfort of abnormal sensations: Some patients complain about the existing low-frequency method.