Transcranial Direct Current Stimulation to Lessen Neuropathic Pain After Spinal Cord Injury: A Mechanistic PET Study

Background. It is suggested that transcranial direct current stimulation (tDCS) can produce lasting changes in corticospinal excitability and can potentially be used for the treatment of neuropathic pain. However, the detailed mechanisms underlying the effects of tDCS are unknown. Objective. We investigated the underlying neural mechanisms of tDCS for chronic pain relief using [F-18]-fluorodeoxyglucose positron emission tomography ([F-18] FDG-PET). Methods. Sixteen patients with neuropathic pain (mean age 44.1 +/- 8.6 years, 4 females) due to traumatic spinal cord injury received sham or active anodal stimulation of the motor cortex using tDCS for 10 days (20 minutes, 2 mA, twice a day). The effect of tDCS on regional cerebral glucose metabolism was evaluated by [F-18] FDG-PET before and after tDCS sessions. Results. There was a significant decrease in the numeric rating scale scores for pain, from 7.6 +/- 0.5 at baseline to 5.9 +/- 1.8 after active tDCS (P =.016). We found increased metabolism in the medulla and decreased metabolism in the left dorsolateral prefrontal cortex after active tDCS treatment compared with the changes induced by sham tDCS. Additionally, an increase in metabolism after active tDCS was observed in the subgenual anterior cingulate cortex and insula. Conclusion. The results of this study suggest that anodal stimulation of the motor cortex using tDCS can modulate