The effect of antispastic agents on motor reflexes in incomplete spinal cord injury - Rehabilitation Institute of Chicago

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Fri, June 3

Speaker: Virginia Chu (Neurolocomotion lab, with Drs. Schmit & Hornby)

Title: The effect of antispastic agents on motor reflexes in incomplete spinal cord injury.

Abstract:  Spasticity is a common complication following a traumatic injury to the spinal cord.
Typical treatments for spasticity in chronic spinal cord injury (SCI) include a prescription of antispastic oral medication with hopes to improve motor function by reducing spasticity. Two commonly prescribed antispastic agents are baclofen and tizanidine. Baclofen is a GABAB agonist and tizanidine is a noradrenergic á2 agonist. Assessments of the treatment of spastic behaviors are typically performed under passive conditions, which do not necessarily parallel the behaviors during functional motor tasks. Functional assessment of motor tasks following administration of antispastic agents have revealed mixed results. Thus, a comprehensive and well-controlled study of antispastic agents on functional tasks is needed to provide insights for clinical decisions.
We examined in detail the changes in spastic response, strength, coordination, and recruitment of voluntary drive in response to a single dose of baclofen or tizanidine in patients with chronic incomplete SCI. The participants attended 3 sessions, spaced at least 1 week apart. During each session, they would receive one of the drugs, tizanidine, baclofen, or placebo, which were administered in a double-blind randomized manner. The participants were assessed before and after drug administration. During the assessments, the participant was placed in a BIODEX chair, with a single joint motor that will move the limb into different postures.

Surface EMG electrodes were used to collect EMG data. The series of assessments include:

1. stretch reflex at the ankle
2. flexor withdrawal reflex elicited with an electrical stimulation at the foot sole area
3. maximum contraction during robot-assisted isokinetic movements
4. maximum isometric knee extension and flexion torque.

Reduced spasm and reflex activity was observed in the post-drug tests of both tizanidine and baclofen. However, the effect of tizanidine and baclofen on strength for isometric and isokinetic tasks varied amongst different participants. Based on the results in this study, we will look at the effects of baclofen and tizanidine on reflex activity during walking. We anticipate that baclofen and tizanidine will suppress the reflex function that produces useful muscle activity in SCI subjects, and result in altered walking performance.