Effects of Transcranial Direct Current Stimulation (tDCS) on Chronic Pain in Spinal Cord Injured Patients

Abstract

Introduction: Pain following spinal cord injury (SCI) is notoriously difficult to manage and often refractory to treatment. Novel approaches, such as non-invasive brain stimulation, targeting central mechanisms associated with chronic pain, have shown early promise as a safe treatment in various patient groups, including spinal cord injury. To date the number of small clinical trials using non-invasive brain stimulation to treat chronic pain in SCI have produced mixed results (1). We report here the findings of a UK based trial examining the effects of anodal Transcranial Direct Current Stimulation (tDCS) administration on pain in spinal injury patients. Methods: Sixteen spinal injury patients from the National Spinal Injury Centre, Stoke Mandeville Hospital, Aylesbury, UK participated in a single centre, double blind randomized control trial. Patients were randomly allocated to either the active (n=8) or sham (n=8) treatment groups. tDCS was administered by electrodes with anode placement over the dominant M1 and the cathode electrode over the contralateral supra-orbit scalp area. Subjects received either active (2mA anodal current) or sham tDCS for 20 minutes daily treatment for 5 consecutive days with the dose based on previously reported chronic pain studies in spinal cord injury patients. A mixed ANOVA was used to evaluate both tDCS treatment and time effects on validated assessment measures for pain and depression up to 2 weeks following treatment intervention. Results: No adverse effects of the treatment were observed in this study, nor were there any significant differences between groups in rating perception of stimulation. While treatment appeared to have reduced group pain scores on a visual analogue scale (VAS), there were no statistically significant differences between active and sham treatment groups when re-examined at the two week follow up. Conclusions: There was a reduction in self-assessed VAS pain score in our small group of SCI patients during treatment in both the sham and active tDCS and at two weeks post treatment. However, our study appears to indicate only a placebo-like effect of tDCS on chronic pain in SCI and no effect attributable to the active anodal stimulation over motor cortex. We also did not observe any significant effects over time or treatment on neuropathic pain when assessed with validated measures. We observed trends of non-significant reduction in some of self-assessed pain scores of measures, however, these are inconclusive. Studies of clinical efficacy of pain treatment by tDCS in spinal cord injury should therefore be conducted on a larger scale, and with a longer follow up period to address the limited evidence available.