Comparison of Conventional and Kilohertz Frequency Epidural Stimulation in Patients Undergoing Trialing for Spinal Cord Stimulation: Clinical Considerations

Objective

Compare therapeutic response of patients to conventional versus high-frequency spinal cord stimulation (SCS).

Methods

Twelve patients with back and leg pain who met standard clinical criteria for a trial of conventional SCS (low-frequency stimulation [LFS]) participated in a half-day session of high-frequency stimulation (HFS) during their weeklong conventional trial. HFS consisted of frequencies ranging from 50 Hz to 4 kHz, or 100 Hz to10 kHz, at constant voltage settings increasing from 0.5 V to 10 V. Visual Analog Scale scores from 0 to10 were recorded, along with notes of any clinical discomfort and open patient comments.

Results

Two of 12 patients had no benefit from either LFS or HFS. In the remaining 10 patients, paresthesias were significantly altered by HFS, and four experienced complete elimination of paresthesias. Five patients preferred HFS to LFS, with an additional three preferring both equally. Abrupt sensation to the onset of HFS was described in six patients, and in ten patients, HFS allowed maximum voltage stimulation of 10 V without discomfort. The four patients who did not have a successful trial of stimulation had significantly longer duration of pain compared to the eight patients who went on to permanent implant (11.2 vs. 4.3 years, P = 0.04).

Conclusions

HFS significantly altered the feeling of paresthesias in the majority of patients (ten of 12), was preferred to LFS in five of 12 patients, and non-inferior to LFS in eight of 12 patients. Both 4 kHz and 10 kHz stimulation allowed patients to benefit from HFS. HFS allowed maximum voltage stimulation without discomfort.

Introduction

Spinal cord stimulation (SCS) is projected to be a $2.3 billion component of the overall neuromodulation market in 2016.¹ At present, 35,000 people are implanted with spinal cord stimulators globally each year.² Failed back surgery syndrome (FBSS) indications for SCS account for roughly 70% of these implantations.³

Recent attention has been brought to high-frequency epidural stimulation as a potential superior modality for relief of back pain.4, 5, 6 Alternate stimulation parameters have also been suggested.7, 8 These modalities propose to offer pain relief without paresthesias. The technological tradeoff for higher-frequency stimulation may be greater use of battery power than conventional SCS.

Despite newer evidence suggesting the advantages of higher-frequency stimulation, the majority of patients implanted today have conventional stimulators that operate with lower-frequency parameters. Few studies have been performed to explore the relative clinical advantages of higher-frequency spinal cord stimulation. Kapural⁶ recently reported the results of a large, randomized, controlled trial of 198 patients comparing high-frequency stimulation to traditional SCS, suggesting superior back and leg pain relief in the high-frequency group. Smith⁹ reported improvement of 2 patients initially treated with low-frequency (40 Hz) and then switched to high-frequency (1 kHz) stimulation. Perruchoud¹⁰ presented a randomized, double-blind, placebo-controlled trial in 40 patients comparing the effects of 5 kHz stimulation to sham stimulation against a conventional stimulation baseline, finding mixed results in terms of the demonstrable benefits of HFSCS.

We seek to expand upon these findings and investigate the potential for clinical advantage by varying both stimulation frequency and voltage in patients undergoing a conventional trial of spinal cord stimulation. In particular, we propose to systematically measure the effect of spinal cord stimulation on clinical pain relief (visual analog scale [VAS]) at frequencies ranging from 50 Hz−10kHz and voltages from 0.5V−10V. Patient observations and discomfort were also noted.