Mechanisms and Outcome-Prognostication for Paresthesia-based and -Free Spinal Cord Stimulation

Over 7 million Canadians suffer from chronic pain with 1 in 4 patients having neuropathic pain (NP), a condition caused by injury to nerves in the body. NP tends to have an extremely unpleasant character, severe intensity, and a persistent unremitting course. Conventional medical management (CMM) is often ineffective in relieving NP in majority of these patients. Paresthesia-Based Spinal Cord Stimulation (PB-SCS) has been used to treat NP but it has limitations in terms of preserving analgesic benefit and it is often associated with adverse effects. Recently introduced Paresthesia-Free SCS (PF-SCS), available at all tertiary level pain centers, has the potential to overcome these limitations but knowledge gaps remain in understanding and applying this modality.

The study design will be a prospective, exploratory study with randomization of order of no stimulation with novel modes of PF-SCS during the SCS trial and blinding of subjects (as per clinical standard of care) and outcome assessors. Participants with appropriate indications for trial of SCS with novel paresthesia-free modes will be enrolled. Baseline demographic and pain-related data including opioid intake in Oral Morphine Equivalents Per day in mg (OMED) will be collected. Pre-SCS trial neuroimaging (fMRI, MEG) and QST will be performed to establish parameters for future comparisons. Data on physical activity and sleep will be collected using actigraphy, as per standard of care. Data on pain and its related domains will be collected using validated questionnaires on the Manage My Pain app, in which all questionnaires administered are part of the patient's clinical standard of care. Ninety subjects will undergo a percutaneous trial of SCS that will last 12 days and the trial will be divided into three phases. All subjects will trial a conventional paresthesia-based SCS mode in the first four days of the trial. Subjects will then proceed the next four days (day 5-8) with no (placebo) stimulation, followed by one of the three novel PF-SCS modes (Burst, High Frequency, High Density) for the last 4 days of the trial. This process is currently adopted for all patients receiving SCS as standard of care. Neuroimaging (fMRI, MEG) and QST will be performed at the end of the SCS trial. Subjects who achieve significant reduction in pain, disability and sleep disturbance questionnaire scores with one of the novel PF-SCS modes will be offered percutaneous implantation of SCS system 4 to 6 weeks after the end of the trial using the novel PF-SCS mode they experienced during the trial. MEG and QST will be performed and data from validated questionnaires on the Manage My Pain app will be collected at 6 months after implantation.

Use of fMRI (functional Magnetic Resonance Imaging), MEG (Magnetoencephalography), and QST (Quantitative Sensory Testing) in this study will help improve understanding of the alteration in brain in NP and the analgesic action of PB/PF-SCS. Validation of wearable technology and of app-based digital platforms will allow these available but infrequently-used modalities to improve success of analgesic treatments in patients with chronic pain. Healthcare systems will benefit through efficient use of resources to treat chronic pain made possible by understanding what works, who does it work for, and how to predict analgesic benefit.

Inclusion criteria

• Adults, 18 - 80 years of age, with refractory neuropathic pain (as per clinical features and DN4 score > 3/10) in back and or lower limbs for more than 3 months following lumbar spine surgery
• Severity of pain > 3/10 on NRS and ODI score for disability >40/100; and
• Pain refractory to conventional medical management tried for at least 3 months.

Exclusion criteria

• Age < 18 or age ≥ 80 years;
• Previous trial or implantation of SCS system;
• Procedural contraindications to SCS including extensive thoracolumbar spine surgery, moderate-to-severe central canal stenosis, coagulopathy, local or systemic infection;
• Pregnancy;
• Opioid dose > 200 mg OMED;
• Psychiatric or psychological disorder likely to impact perception of pain;
• Inability to comply with the study interventions or evaluate treatment outcomes;
• Mechanical spine instability as per flexion/extension lumbar X-rays;
• Ongoing litigation issues related to the pain; and
• Concomitant peripheral neuropathy or myopathy or central neuropathic pain (e.g. post-stroke pain).