Quantification of the effects of an alpha-2 adrenergic agonist on reflex properties in spinal cord injury using a system identification technique

Journal of NeuroEngineering and Rehabilitation, 2010 · DOI: 10.1186/1743-0003-7-29 · Published: June 23, 2010

Spinal Cord Injury Neurology Neurorehabilitation

Simple Explanation

This study investigates how tizanidine, a drug used to treat muscle spasticity, affects reflexes and muscle properties in people with spinal cord injuries. The goal was to understand how tizanidine works to reduce spasticity. Researchers applied small stretches to the ankle joints of spinal cord injured participants and measured the resulting forces. They used a special technique to separate the muscle's own stiffness from the stiffness caused by reflexes. The study found that tizanidine mainly reduces the reflex response in muscles, without significantly changing the muscle's own stiffness. This suggests the drug's primary action is on the reflex pathways involved in spasticity.

Study Duration

Not specified

Participants

21 spinal cord injured subjects

Evidence Level

Not specified

Key Findings

1
Tizanidine significantly decreased stretch-evoked joint torque at the ankle (p < 0.001).
2
The peak torque was reduced between 15% and 60% among the spinal cord injured subjects, with an average reduction of 25%.
3
Reflex stiffness decreased significantly across a range of joint angles (p < 0.001) after using tizanidine, while there were no significant changes in intrinsic muscle stiffness.

Research Summary

This study quantified the effects of a single dose of tizanidine on the neuromuscular abnormalities associated with spasticity, focusing on reflex and intrinsic neuromuscular properties. The findings indicate that tizanidine's actions on stretch reflexes in spastic subjects are substantial, take effect quickly, and occur at a relatively small dose. The study affirms that the effects of tizanidine on limb spasticity are mediated by reflex changes, rather than direct changes in muscle contractility.

Practical Implications

Clinical Decision Aid

A single 'test' dose of Tizanidine may help clinicians decide whether the drug can helpful in controlling symptoms.

Targeted Treatment

Tizanidine primarily affects reflex mechanisms, allowing for more targeted treatment of spasticity without directly altering muscle properties.

Predictive Efficacy

Response to a low dose of tizanidine may predict the clinical/therapeutic efficacy of the drug.

Study Limitations

1
The study used a single dose of tizanidine, limiting conclusions about long-term effects.
2
The inter-subject variability in reflex stiffness changes was high from mid-plantarflexion to full-dorsiflexion.
3
The study focused on individuals with incomplete spinal cord injuries, potentially limiting generalizability to other populations.

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