Closed Loop Spinal Cord Stimulation for Neuromodulation of Upper Motor Neuron Lesion Spasticity

Plain-language summary

Spasticity is characterized by increased muscle tension and is a classic consequence of upper motor neuron (UMN) damage in the central nervous system, such as from stroke or trauma. Clinically, it presents as muscle resistance to passive stretching, along with clasp-knife rigidity, clonus, increased tendon reflexes, and muscle spasms. An imbalance of the descending inhibitory and muscle stretch reflexes is thought to be the cause of spasticity. Post-stroke spasticity is a common condition that occurs in 37.5-45% of cases in the acute stage and 19-57.4% in the subacute stage after a stroke. At 6 months post-stroke, spasticity develops in 42.6-49.5% of cases, and at one year, it affects 35-57.4% of individuals. In patients with cerebral palsy (CP), incidence is almost 80% while in those living with spinal cord injury the number approaches up to 93%. Traumatic brain injury (TBI) patients have a higher prevalence on initial admission to neurorehabilitation but one in three patients will have chronic spasticity. However, the Defense and Veterans Brain Injury Center report a rate of TBIs amongst deployed veterans to be around 11-23% mostly from blast and explosive trauma. There have been studies as early as the 1980s exploring the efficacy of SCS for spasticity control, however, the credibility of many of these studies is constrained due to an incomplete comprehension of spasticity's underlying mechanisms, outdated research methods, and early limitations in implantable device technology. Intrathecal pumps for baclofen have remained as the mainstay for refractory spasticity, however, it comes with associated risks such as chemical dependence leading to acute baclofen withdrawal and requiring frequent refill requirement. Most importantly, it does not yield functional improvement of muscle activity, just suppression of spasticity. Botox is also routinely used but due to heterogeneity in muscle involvement as well as variability in provider skill, results may be inconsistent and short-lasting, requiring frequent clinic visits for repeat injections to the affected muscle groups. SCS may be able to address that gap in spasticity management.

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