The Efficacy of High-Density Spinal Cord Stimulation Among Trial, Implant, and Conversion Patients: A Retrospective Case Series

Objectives: Methods of energy delivery for traditional spinal cord stimulation (SCS) systems consist of adjusting programming parameters to affect the total charge delivered per unit time. One high electrical charge delivery method being considered is subthreshold high density (HD) programming. To date, there is limited clinical evidence for the efficacy and safety of paresthesia-free HD programming. The aim of this study was to examine the efficacy and safety of HD programming. Materials and Methods: A retrospective review was performed on HD-programmed SCS patients with a minimum of one year follow-up. Three HD categories were examined: trial, implant, and conversion (i.e., patients with conventional SCS who were converted to HD settings). High density amplitude settings were below paresthesia threshold. Patients were classified as responders to HD if they preferred the paresthesia-free HD setting to the conventional setting and demonstrated >= 50% pain reduction compared to baseline pain score on delivery and no-stimulation related neurological deficit. Adverse effects were documented. Results: Seventeen patients were identified, including 11 conversion patients and six patients who had positive response to HD programming during the trial and then were implanted. For trial/implant and conversion patients, both HD and conventional programming significantly reduced the numerical pain rating scale (NRPS) compared to baseline (p <= 0.026). Pain scores were not significantly different between the HD and traditional programs for the trial (p=0.060), implant (p=0.632), and conversion categories (p=0.658). Through at least 12 months of follow-up, eight (47%) patients continued to be HD responders. Conclusions: In subpopulations, HD programming may be a viable option to deliver subthreshold pain reduction. Randomized, controlled trials with extended follow-up are needed to further evaluate HD programming.