Epidural Spinal Cord Stimulation for Spasticity: a Systematic Review of the Literature

OBJECTIVE:Spasticity is a form of muscle hypertonia secondary to various pathologies, including traumatic brain injury, spinal cord injury, cerebral palsy, and multiple sclerosis. Medical treatments are available however these often result in insufficient clinical response. This review evaluates the role of epidural spinal cord stimulation (SCS) in the treatment of spasticity and associated functional outcomes. METHODS:A systematic review of the literature was performed using the Embase, CENTRAL, and MEDLINE databases. We included studies that utilized epidural SCS to treat spasticity. Studies investigating functional electrical stimulation, transcutaneous SCS, and animal models of spasticity were excluded. We also excluded studies that used SCS to treat other symptoms such as pain. RESULTS:Thirty-four studies were included in the final analysis. The pooled rate of subjective improvement in spasticity was 78% (95% CI 64%-91%, I2 = 77%), 40% (95% CI 7%-73%, I2 = 88%) for increased H reflex threshold or decreased Hoffman-reflex/muscle response wave ratio, and 73% (65%-80%, I2 = 50%) for improved ambulation. Patients with spinal aetiologies had better outcomes compared to cerebral aetiologies. Up to 10% of patients experienced complications including infections and hardware malfunction. CONCLUSIONS:Our review of the literature suggests that SCS may be a safe and useful tool for the management of spasticity, however there is significant heterogeneity amongst studies. The quality of studies is also very low. As such, further studies are needed to fully evaluate the utility of this technology, including various stimulation paradigms across different aetiologies of spasticity.