EVOKE™ Therapy for Chronic Non-surgical Refractory Back Pain: Subgroup Analysis from Two Prospective Multicenter Trials

Introduction: Historically, SCS relied on patient report of paresthesia overlapping the distribution of pain and was most used for persistent spinal pain syndrome type 2 with predominant leg pain.1,2 The use of SCS for non-surgical refractory back pain (NSRBP; also known as persistent spinal pain syndrome type 1), has been less explored due to challenges which hinder adequate coverage of the lower back.3 Innovations in SCS such as the development of EVOKE™ Therapy through physiologic ECAP-controlled closed-loop SCS, overcome limitations of traditional, fixed-output SCS for the treatment of NSRBP.4,5 The aim of this study was to evaluate the neurophysiologic dose that produced pain-related and holistic response for patients with NSRBP.

Methods: Patient-reported outcome measures for pain intensity, physical function, health-related quality of life, sleep quality, emotional function, and change in opioid use were collected from 68 patients with NSRBP in two prospective multicenter clinical trials (NCT02924129, NCT04319887). A validated composite outcome measure comprising 5 different health domains was used to evaluate holistic treatment response through minimal clinically important differences (MCIDs).6,7 EVOKE Therapy, characterized by objective neurophysiologic measurements from the spinal cord in response to ECAP-controlled closed-loop stimulation, provided information on system utilization, closed-loop performance (dose accuracy), and neurophysiologic dose metrics.

Results: Sixty-eight patients with NSRBP received EVOKE Therapy following a temporary trial phase, with 65 and 63 patients included through 3- and 12-months, respectively. At 12-months, 79% of patients reported ≥50% reduction in pain intensity and 48% obtained ≥80% pain relief (Figure 1). Statistically and clinically meaningful improvements in all patient-reported outcome measures assessed were observed at 3- and 12-months. The cumulative responder score which reflects the total number of MCIDs obtained across all 5 domains was 8.7±5.9 MCIDs at 12-months. The Holistic MCID which adjusts the cumulative responder score by the number of impaired baseline domains was 1.8±1.2 at 12-months. Voluntary reduction or elimination of opioid use was observed in approximately half of the patients that were taking opioids at baseline. System utilization was >80%, dose ratio was >1.3 (i.e., 30% above ECAP threshold) with a high dose accuracy keeping the elicited ECAP within 3.5μV of the target ECAP set on the system (Table 1).

Conclusion: Electrical dosing 30% above ECAP threshold reliably improved multiple health domains as measured by a validated composite outcome measure in patients with NSRBP. The neurophysiologic metrics observed were within the ranges recently found to provide maximal analgesic effect in a broader chronic pain population.8 This study suggests EVOKE Therapy is well placed to activate relatively lateral dorsal column fibres (which innervate the lower back) without causing side-effect dorsal root activation.