Long-term efficacy of 1-1.2 kHz subthreshold spinal cord stimulation following failed traditional spinal cord stimulation: a retrospective case series.

BACKGROUND AND
OBJECTIVE: We investigated whether an effective long-term pain relief could be achieved using subthreshold 1-1.2 kHz spinal cord stimulation (SCS) among patients who were initially implanted with traditional paresthesia-based SCS but who failed to maintain an adequate pain relief.
METHODS: Retrospective chart review was conducted of patients' electronic records who underwent a trial of subthreshold 1-1.2 kHz SCS. One hundred and nine patients implanted and programmed at traditional paresthesia-based frequencies 40-90 Hz (low-frequency SCS) with unsatisfactory pain relief or unpleasant paresthesias were identified. Patients' settings were switched to 1-1.2 kHz and 60-210 µs, and variable amplitude adjusted to subthreshold. Pain scores and medication usage were collected. Complete data are presented on 95 patients.
RESULTS: Data were collected from 36 men and 59 women who were converted from above-threshold 40-90 Hz SCS to 1-1.2 kHz SCS, with a minimum follow-up of 12  months. Nearly a third (63/95 or 66.3%) of the subjects deemed 1-1.2 kHz SCS ineffective and returned to low-frequency SCS within 1 week after switch, and one-sixth (16/95 or 16.8%) of the subjects returned to low-frequency SCS within 1 month. Only 13 (13.7%) subjects continued using 1-1.2 kHz subthreshold SCS for 3 months or longer and 2.1% (2/95) of subjects continued using it at 12 months. A comparison of their pain scores and opioid use before and during the time we used 1-1.2 kHz SCS revealed no significant difference.
CONCLUSION: The results from our single center failed to show additional long-term clinical benefit of 1-1.2 kHz subthreshold SCS in patients with chronic pain failing traditional low-frequency SCS. © American Society of Regional Anesthesia & Pain Medicine 2019. No commercial re-use. See rights and permissions. Published by BMJ.