Spinal Cord Stimulation: Clinical Efficacy and Potential Mechanisms

Abstract

Spinal cord stimulation (SCS) is a minimally invasive therapy used for the treatment of chronic neuropathic pain. SCS is a safe and effective alternative to medications such as opioids, and multiple randomized controlled studies have demonstrated efficacy for difficult-to-treat neuropathic conditions such as failed back surgery syndrome. Conventional SCS is believed mediate pain relief via activation of dorsal column Aβ fibers, resulting in variable effects on sensory and pain thresholds, and measurable alterations in higher order cortical processing. Although potentiation of inhibition, as suggested by Wall and Melzack's gate control theory, continues to be the leading explanatory model, other segmental and supraspinal mechanisms have been described. Novel, non-standard, stimulation waveforms such as high-frequency and burst have been shown in some studies to be clinically superior to conventional SCS, however their mechanisms of action remain to be determined. Additional studies are needed, both mechanistic and clinical, to better understand optimal stimulation strategies for different neuropathic conditions, improve patient selection and optimize efficacy.

Keywords: complex regional pain syndromes; low back pain; pain syndromes; postoperative pain; regional complex; spinal cord stimulation.

Fig. 1.. Spinal cord stimulation lead position.

The electrical lead sits in the epidural space, and the electrical stimuli activate fibers directly below it. This causes initiation of orthodromic and antidromic action potentials and supraspinal and segmental effects. Adapted from Smits et al., 2013.

Fig. 2.. Waveform properties.

(A) The amount of charge delivered to tissues depends on pulse properties: shape, amplitude, and duration. The lower panel illustrates the concept of frequency and charge balance. (B) Burst waveform, adapted from De Ridder et al. The waveform represents five, 1-ms-long pulses, delivered at 500 Hz, while the burst frequency is 40 Hz. Charge balance occurs after the five pulses.