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

Abstract

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. 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. 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. 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.