Transcutaneous spinal stimulation as a therapeutic strategy for spinal cord injury: state of the art

Abstract

Leandro H Grecco,1,3,4,* Shasha Li,1,5,* Sarah Michel,1,6,* Laura Castillo-Saavedra,1 Andoni Mourdoukoutas,7 Marom Bikson,7 Felipe Fregni1,21Spaulding Neuromodulation Center, Spaulding Rehabilitation Hospital, Harvard Medical School, Boston, MA, 2Spaulding-Harvard Spinal Cord Injury Model System, Spaulding Rehabilitation Hospital, Harvard Medical School, Charlestown, MA, USA; 3Special Laboratory of Pain and Signaling, Butantan Institute, 4Department of Pharmacology, Institute of Biomedical Science, University of São Paulo, São Paulo, Brazil; 5Department of Rehabilitation Medicine, West China Hospital, Sichuan University, Chengdu, Sichuan, People's Republic of China; 6Department of Pharmacy and Biomedical Sciences, University of Namur, Belgium; 7Department of Biomedical Engineering, The City College of New York, New York, NY, USA*These authors contributed equally to this workAbstract: Treatments for spinal cord injury (SCI) still have limited effects. Electrical stimulation might facilitate plastic changes in affected spinal circuitries that may be beneficial in improving motor function and spasticity or SCI-related neuropathic pain. Based on available animal and clinical evidence, we critically reviewed the physiological basis and therapeutic action of transcutaneous spinal cord stimulation in SCI. We analyzed the literature published on PubMed to date, looking for the role of three main noninvasive stimulation techniques in the recovery process of SCI and focusing mainly on transcutaneous spinal stimulation. This review discusses the main clinical applications, latest advances, and limitations of noninvasive electrical stimulation of the spinal cord. Although most recent research in this topic has focused on transcutaneous spinal direct current stimulation (tsDCS), we also reviewed the technique of transcutaneous electric nerve stimulation (TENS) and neuromuscular electrical stimulation (NMES) as potential methods to modulate spinal cord plasticity. We also developed a finite element method (FEM) model to predict current flow in the spinal cord when using different electrode montages. We identified gaps in our knowledge of noninvasive electrical stimulation in the modulation of spinal neuronal networks in patients with SCI. tsDCS, TENS, and NMES have a positive influence on the promotion of plasticity in SCI. Although there are no randomized controlled studies of tsDCS in SCI, preliminary evidence is encouraging. FEMs predict that tsDCS electrode montage can be used to shape which spinal segments are modulated and what detailed areas of spinal anatomy can concentrate current density (eg, spinal roots). tsDCS is a technique that can influence conduction along ascending tracts in the spinal cord, so could modulate supraspinal activity. It may also be a promising new approach for a number of neuropsychiatric conditions.Keywords: spinal cord injury, transcutaneous spinal direct current stimulation, transcutaneous electric nerve stimulation, neuromuscular electrical stimulation, motor, spasticity, pain