Abstract
Background
Neuropathic pain NP is common in spinal cord injury SCI patients. One of its manifestations is a lowering of pain perception threshold in quantitative thermal testing QTT in dermatomes rostral to the injury level. Transcranial direct current stimulation tDCS combined with visual illusion VI improves pain in SCI patients. We studied whether pain relief with tDCS + VI intervention is accompanied by a change in contact heat- evoked potentials CHEPs or in QTT.
Methods
We examined 18 patients with SCI and NP before and after 2 weeks of daily tDCS + VI intervention. Twenty SCI patients without NP and 14 healthy subjects served as controls. We assessed NP intensity using a numerical rating scale NRS and determined heat and pain thresholds with thermal probes. CHEPs were recorded to stimuli applied at C4 level, and subjects rated their perception of evoked pain using NRS during CHEPs.
Results
Thirteen patients reported a mean decrease of 50% in the NRS for NP after tDCS + VI. Evoked pain perception was significantly higher than in the other two groups, and reduced significantly together with CHEPs amplitude after tDCS + VI with respect to baseline. Pain perception threshold was significantly lower than in the other two groups before tDCS + VI intervention, and increased significantly afterwards.
Conclusion
Two weeks of tDCS + VI induced significant changes in CHEPs, evoked pain and heat pain threshold in SCI patients with NP. These neurophysiological tests might be objective biomarkers of treatment effects for NP in patients with SCI.