EVOKE™ Therapy for Complex Regional Pain Syndrome: A Subgroup Analysis of the ECAP Study

Introduction: Complex regional pain syndrome (CRPS) is a debilitating pain disorder characterized by severe pain that is disproportionate in magnitude or duration to the expected course after similar injury.1,2 Biopsychosocial factors may interact to trigger CRPS, although the precise mechanisms are unclear.3 Neuromodulation interventions such as spinal cord stimulation (SCS) are recommended by international guidelines for patients with CRPS who have not responded to conventional medical management.1 EVOKE™ Therapy through ECAP-controlled closed-loop SCS has demonstrated incremental benefits over fixed-output SCS for chronic refractory back and leg pain up to 36-months follow-up.4-6 The current study presents the first evaluation of EVOKE Therapy for CRPS in addition to holistic treatment response and the neural dosing that produced the treatment effect.

Methods: The ECAP Study was a prospective, multicenter, single-arm study conducted at 22 sites throughout the United States to collect routine clinical care data while applying a rigorous data collection approach consistent with RCT methodology.7 The current subgroup analysis comprises adult patients whose baseline pain assessment for pain source was listed as CRPS I or CRPS II. Holistic treatment response was assessed using validated methods previously described8,9 and considered seven domains from the PROMIS-29 questionnaire. Minimal clinically important differences (MCIDs) were used to characterize response to EVOKE Therapy at maximal analgesic effect post-implant visit. 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: Twenty-one patients with CRPS received EVOKE Therapy following a temporary trial phase. A mean >1 MCID was obtained for all domains and >2 MCIDs were obtained for five of the seven domains at post-implant visit (Figure 1). The cumulative responder score which reflects the total number of MCIDs obtained across the PROMIS-29 domains was 12.4±7.9. The Holistic MCID which adjusts the cumulative responder score by the number of impaired baseline domains was 2.4±1.1. Most patients (95%) were considered holistic MCID responders, i.e., obtained ≥1 holistic MCID. EVOKE Therapy consisted of system utilization of 88%, dose ratio of 1.3 (i.e., 30% above ECAP threshold) with a high dose accuracy keeping the elicited ECAP within 3.6μV of the target ECAP set on the system (Table 1).

Conclusion: EVOKE Therapy can provide profound clinical benefits for patients with CRPS. Physiologic therapy metrics show consistent neural activation for patients with CRPS in line with previous reports of closed-loop SCS.10