Spinal cord stimulation:Carry-over effects on spasticity

Spasticity presents a major cause of disability following a spinal cord injury, further deteriorates voluntary control over movements including walking, causes pain, and negatively impacts independence and quality of life. Its successful management while preserving residual mobility by standard-of-care therapies has remained difficult. A complementary intervention proven to ameliorate severe spinal spasticity is spinal cord stimulation via implanted electrodes. The underlying principle is to partially substitute the missing or altered brain control over the spinal cord below the injury by means of electrical stimulation and thereby regulate the processing of naturally generated neural signals at the level of the spinal cord. However, the use of this technique in motor disorders has remained relatively rare, also because of its invasive character, the time-consuming testing phase for its effective application, and the lack of markers to identify responders in advance. With the emergence of a skin-electrode based method of spinal cord stimulation, co-developed by Ursula Hofstoetter, Austrian principal investigator of the present study, the non-invasive activation of the same neural structures as with the implanted electrodes became possible, using standard equipment available at rehabilitation centers. Previous proof-of-concept studies (co-principal investigator: U. Hofstoetter) suggested that this method may produce remarkable therapeutic outcomes in spinal cord injured individuals. Specifically, a single 30-minute stimulation session was shown to control spasticity and augment residual motor control for several hours after its application. Data collected in one subject in whom the stimulation was repetitively applied for 6 weeks suggested that such therapy may result in cumulative therapeutic outcomes lasting for considerably prolonged periods of time. In collaboration with the Swiss Paraplegic Center Nottwil and the Swiss principal investigator Angela Frotzler, the present study is the first clinical study specifically dedicated to explore whether repetitive stimulation applications may induce lasting therapeutic effects on spinal spasticity and residual mobility. In 32 patients with incomplete spinal cord injury, the effects of intermittent stimulation for 6 weeks as a home-based therapy as well as their temporary persistence after the discontinuation of the stimulation will be studied. In parallel, spinal neural mechanisms associated with the development of spasticity and their modifications by the transcutaneous stimulation will be studied, a research question that has not been addressed so far. If proven effective, noninvasive spinal cord stimulation through skin electrodes has the great potential to considerably augment the outcomes of contemporary neurorehabilitation strategies and to lead to individually optimized levels of functional recovery of those who suffer from traumatic spinal cord injuries.