Motor cortical excitability behavior in chronic spinal cord injury neuropathic pain individuals submitted to transcranial direct current stimulation—case reports

Abstract

Introduction: Increased excitability of the motor cortex through transcranial direct current stimulation (tDCS) has been described as a non-pharmacological strategy for the treatment of Spinal Cord Injury neuropathic pain (SCINP). It is also believed that the ability to enhance motor cortex excitability (MCE) could be impaired within chronic SCINP individuals. The following case reports describe the MCE behavior in individuals with chronic SCINP submitted to electrical non-invasive neuromodulation. Case presentations: This article reports 11 cases with chronic SCINP in which each individual was submitted to a 5-day pre-post MCE analysis in order to evaluate its behavior after the anodal tDCS sessions. All cases maintained ongoing pharmacological treatment. Four individuals have shown negative variation of the MCE, two of which reported pain intensity reduction. Three other individuals had MCE-positive variation along 5 days, from which only one reported a VAS 0.5 pain reduction after the 5th day of observation. The other four individuals did not present significant variation of the MCE. Discussion: The positive variation of MCE was significantly altered by adjunctive tDCS only in three individuals, though no clinically relevant reduction in pain intensity was reported among these participants. Key factors such as pain and injury duration, age, chronic medication use and underlying maladaptive neuroplasticity may influence responsiveness to brain stimulation within this population. These case reports try to add evidence for cautious recommendation of tDCS in chronic SCINP individuals and to the necessity of identifying groups of individuals that are most susceptible to neuromodulation.