Carry-over Effects of Repetitively Applied Transcutaneous Spinal Cord Stimulation on Spasticity

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Spinal cord injury is a devastating condition, causing substantial impairment of vital body functions caudal to the lesion. A major cause of disability stems from spasticity, a common secondary sequelae. Its various clinical manifestations include spasms, clonus, and resistance to passive movements, and often present a major hindrance in rehabilitation, further deteriorate residual motor performance, and negatively impact independence and quality of life. Despite its high prevalence, successful management of spasticity has remained difficult. Standard-of-care treatment modalities are often insufficient or bear the risk of undesirable side effects further accentuating paresis. Epidural stimulation of the lumbar spinal cord via implanted electrodes provides for an alternative approach. It works through modifying the dysregulated neural signal processing of spared spinal circuitry caudal to the injury. Its ameliorative effects on severe lower-limb spasticity have been repetitively reported. Yet, epidural spinal cord stimulation in motor disorders is still off-label, applied in relatively few patients only, 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 development of transcutaneous spinal cord stimulation, a method became available to activate the same input structures to the lumbar spinal cord as with epidural stimulation and hence to induce similar neuromodulatory effects, yet non-invasively, using standard equipment available at rehabilitation centers. A recent proof-of-concept study has shown that a single 30-minute session of transcutaneous spinal cord stimulation controlled various clinical signs of spasticity and augmented residual motor control in spinal cord injured individuals for several hours beyond its application. Further, in one subject, the stimulation was repetitively applied for six weeks, resulting in cumulative therapeutic effects persisting for 10 days after its discontinuation. These observations strongly suggest that the stimulation can induce beneficial neuroplastic adaptations of spared spinal systems and their interaction with residual supraspinal control. The proposed research aims at studying the reproducibility of these findings in a statistically sound cohort of individuals with spinal cord injury and testing the applicability and acceptance of transcutaneous spinal cord stimulation as a home-based therapy.

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