The Effect of Paired Associative Stimulation with High-intensity Cortical Component and High-frequency Peripheral Component on Neuropathic Pain in Incomplete Spinal Cord Injury Patients

Study design: A prospective interventional sham-controlled pilot study Objectives: To investigate the effect of motor tract paired associative stimulation consisting of high-intensity transcranial magnetic stimulation and high-frequency electric stimulation of peripheral nerves (high-PAS) on moderate-to-severe upper limb neuropathic pain in incomplete spinal cord injury patients and compare it to sham treatment in the same patients. Setting: BioMag Laboratory, HUS Diagnostic Center, University of Helsinki and Helsinki University Hospital, Helsinki, Finland. Methods: High-PAS was applied for four weeks to five patients with incomplete, non-traumatic SCI and chronic neuropathic pain in upper limb(s). Median, ulnar, and radial nerves of more painful hand were stimulated. The same patients received also sham stimulation for four weeks. Pain was measured with Verbal Rating Scale (VRS) weekly and with Brief Pain Inventory before and after both stimulation periods and after follow-up of eight weeks. Results: Clinically significant pain relief was not achieved with neither high-PAS, nor sham treatment. Conclusions: High-PAS targeting motor tract was not effective in treatment of severe post-SCI neuropathic pain. Nevertheless, pain is not a contraindication for high-PAS in rehabilitation. Previously reported positive effect on milder neuropathic pain may be linked to improved muscle activity or different type of pain or explained by placebo effect. High-PAS targeting sensory tracts instead of motor tracts merits further investigation for pain treatment. Trial registration: clinicaltrials.gov, ID NCT05362422