Purpose: There remains an unmet clinical need for the development of new therapeutic approaches for the treatment of pain. Recent findings have confirmed significant changes in the pain-related neural networks among patients with chronic pain, opening novel possibilities for investigation. Two non-invasive techniques (transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS)) have emerged as interesting, effective, and promising modalities for pain relief.
Methods: Here we review the clinical efficacy of these techniques for the treatment of pain through an updated systematic meta-analysis on the effects of primary motor cortex stimulation on pain and we discuss potential mechanisms of action based on insights from brain stimulation studies. Our meta-analysis includes 18 studies, which together show that non-invasive brain stimulation is associated with an effect size of -0.86 (95% C.I., -1.54, -0.19) on a standardized pain scale ranging from 0 (no pain) to 10 (worst pain possible).
Results and conclusions: Besides its use as a therapeutic tool, non-invasive brain stimulation can also be used to measure cortical reactivity and plasticity in chronic pain. Such measurements could potentially be used as biomarkers for the dysfunctional chronic pain-related neural network and might be helpful in measuring the efficacy of interventions designed for chronic pain.