American Society for Peripheral Nerve

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High Frequency Alternating Current Neural Blockade as an Alternative Treatment for Spasticity
Diego L. Guarin, PhD1; Joseph R Dusseldorp, MBBS, MS, FRACS2; Nate Jowett, MD1
1Harvard University, Boston, MA; 2The University of Sydney, Sydney, Australia

Introduction:
Spasticity is a vexing clinical problem causing considerable patient morbidity and caregiver burden, and is estimated to affect more than 12 million people worldwide. Neural blockade by means of high-frequency alternating current (HFAC) delivery to affected peripheral nerves has been postulated as a management strategy. However, the effectiveness of this treatment has never been tested in an animal model of spasticity. Herein, the effectiveness of HFAC to dampen aberrant spinal reflex responses in a mammalian model of spasticity is demonstrated for the first time.

MATERIALS AND METHODS:
Sacral spinal cord injury to induce hindlimb spasticity or sham surgery was performed in Lewis rats. After 8 weeks, the sciatic nerve was exposed and nerve cuff electrodes placed under general anesthesia for delivery of proximal HFAC neural blockade and distal sub-threshold electrical stimulation. Stimulation comprised short (5ms) biphasic pulses at 1 Hz, and blockade comprised a 10 V (peak-to-peak), 10 kHz sinusoidal alternating current. Tensiometry was used to measure force generated at the ankle joint during sciatic stimulation in awake animals, with and without proximal neural blockade.

RESULTS:
Sham animals demonstrated no observable force response to sub-threshold stimuli, either with or without neural blockade. In contrast, spastic animals demonstrated large force responses in response to sub-threshold electrical stimulation in the absence of proximal neural blockade; this behavior is expected in the spastic joint. Force responses demonstrated latencies of 11.8 1 ms with durations of 64 2 ms. Force responses to electrical stimuli in spastic animals were suppressed below detectable levels in the presence of proximal HFAC neural blockade.CONCLUSION:
Neural blockade by HFAC delivery to peripheral nerves appears effective for instantaneously squelching of spastic responses in limbs. This approach holds promise for development of implantable peripheral neuroprosthetics for management of spasticity.


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