High-frequency Alternating Current Stimulation for Neurophatic Pain in Spinal Cord Injury

Neuropathic pain affects more than a third of people with spinal cord injuries, reducing their quality of life, and the effectiveness of current treatments is limited. The latest research on healthy volunteers has shown that transcutaneous electrical stimulation with high-frequency blocking currents could have a potential effect on pain, proving to be a safe intervention.

To investigate the safety and effectiveness of transcutaneous electrical stimulation with 40 kHz alternating currents combined with standard treatment compared to placebo electrical stimulation plus standard treatment for neuropathic pain in people with spinal cord injury.

Design: Parallel, randomised, double-blind, placebo-controlled pilot clinical trial.

Participants and location: People with spinal cord injury over the age of 18, with a history of more than three months, neuropathic pain at the level of injury and/or below the level of injury, and pain intensity ≥ 30 mm on the visual analogue scale (VAS) for pain. Participants with any contraindications for the application of transcutaneous electrical stimulation will be excluded. The study will be conducted at the National Hospital for Paraplegics in Toledo.

Intervention: Participants will be randomly assigned to two intervention groups:

Active group (n=15) transcutaneous electrical stimulation with 40kHz alternating currents and Placebo group (n=15) simulated stimulation. The duration of the session in both interventions will be 20 minutes, 10 sessions, over two weeks (5 sessions/week).

Main variables and measurement instruments: The main variable will be the Spanish version of the Neuropathic Pain Symptom Inventory. Secondary variables will be pain perception, which will be assessed using a daily record of spontaneous pain with the VAS scale. The intensity of pain evoked by mechanical stimuli will be assessed using the VAS scale, and pain evoked by thermal stimuli will be assessed using a quantitative sensory test with a Peltier thermode. An ad hoc questionnaire has been designed to assess adverse effects. The assessments will be carried out at four time points: before the intervention, during the intervention, immediately after the intervention, and one week after the intervention.

Inclusion criteria

• People with spinal cord injuries of any aetiology affecting the D1 spinal cord level or lower (paraplegia)
• With injury grade A, B, C, or D according to the ASIA (American Spinal Injury Association) Impairment Scale (AIS)
• Time since spinal cord injury ≥ 3 months
• A score of ≥ 4 points on the Dolour Neuropathique 4 (DN4) scale
• Neuropathic pain at the level of the injury (within the dermatome at that level and up to three dermatomes below) and/or below the level of the injury (more than three dermatomes below)
• Duration of pain ≥ 1 month
• Average pain perception score ≥ 30 mm on the visual analogue scale (VAS) in the week prior to eligibility, with a daily record of 5 days (Monday to Friday) in the morning.
• Be able to understand instructions and assessment tools
• Agree to participate in the study and sign the informed consent form

Exclusion criteria

• Cauda equina injuries
• Brain injuries or other central nervous system injuries concomitant with spinal cord injury
• A value of 100 mm in any of the daily records collected in the week prior to eligibility
• Having any contraindications for the application of transcutaneous electrical stimulation: cardiac pacemaker or any other implanted electrical device, epilepsy, pregnancy, active malignant tumours in the area of application of the stimulation, and wounds or skin damage in the area of stimulation
• History of psychiatric illness
• Major depression
• Spinal cord injury caused by autolysis
• Changes in medication prescribed for the treatment of pain and spasticity during the study
• Acute nociceptive pain in any area of the body during the study