Modification of spasticity by transcutaneous spinal cord stimulation in individuals with incomplete spinal cord injury

Context/objective: To examine the effects of transcutaneous spinal cord stimulation (tSCS) on lower-limb spasticity. Design: Interventional pilot study to produce preliminary data. Setting: Department of Physical Medicine and Rehabilitation, Wilhelminenspital, Vienna, Austria. Participants: Three subjects with chronic motor-incomplete spinal cord injury (SCI) who could walk >= 10 m. Interventions: Two interconnected stimulating skin electrodes (phi 5 cm) were placed paraspinally at the T11/T12 vertebral levels, and two rectangular electrodes (8 x 13 cm) on the abdomen for the reference. Biphasic 2 ms-width pulses were delivered at 50 Hz for 30 minutes at intensities producing paraesthesias but no motor responses in the lower limbs. Outcome measures: The Wartenberg pendulum test and neurological recordings of surface-electromyography (EMG) were used to assess effects on exaggerated reflex excitability. Non-functional co-activation during volitional movement was evaluated. The timed 10-m walk test provided measures of clinical function. Results: The index of spasticity derived from the pendulum test changed from 0.8 +/- 0.4 pre-to 0.9 +/- 0.3 post-stimulation, with an improvement in the subject with the lowest pre-stimulation index. Exaggerated reflex responsiveness was decreased after tSCS across all subjects, with the most profound effect on passive lower-limb movement (pre-to post-tSCS EMG ratio: 0.2 +/- 0.1), as was non-functional co-activation during voluntary movement. Gait speed values increased in two subjects by 39%. Conclusion: These preliminary results suggest that tSCS, similar to epidurally delivered stimulation, may be used for spasticity control, without negatively impacting residual motor control in incomplete SCI. Further study in a larger population is warranted.