High-frequency transcutaneous cervical electrical stimulation: A pilot study

Abstract

Early results suggest that transcutaneous stimulation of cervical regions may have a positive effect on recovery of upper limb motor function after neurological injuries. However, in clinical applications, patients find transcutaneous low-frequency spinal cord stimulation (LF-tSCS) unpleasant. Transcutaneous high-frequency spinal cord stimulation (HF-tSCS) has been presented as an option to reduce pain and discomfort produced by LF-tSCS. We performed a pilot study with 3 participants to compare the effects of HF-tSCS and LF-tSCS on upper limb reflex responses and reported pain level and discomfort. In the first part of the experiment, high- (i.e., monophasic and biphasic burst) vs low-frequency (i.e., monophasic pulse) single waveform cervical tSCS was applied and motor response threshold identified via electromyography (EMG). In the second part of the experiment, the three waveforms were administered as train pulses and the stimulation intensity was increased in four steps from 20% to 80% of the individual motor response threshold. Participants indicated the pain level for each stimulation intensity increment and waveform. We find that participants reported stronger discomfort in HF-tSCS than LF-tSCS stimulation at motor threshold level. Further, stimulation at subthreshold level was associated with strong discomfort in HF- and LF-tSCS train pulses, especially in participants with relatively high motor response threshold. We conclude that cervical HF-tSCS may not (yet) be an option for clinical application, even though acceptability may depend on the individual motor response threshold of the patient