Examination of Mechanisms Involved in Spasticity Reduction after BTX-A Injection in Hemiplegic Patients

Document Type : Research Paper




ntroduction: Spasticity is a common and disabling complication that occurs as a result of upper motor neuron lesion. Recently, Botulinum Toxin – A (BTX-A) has received a pronounced position in spasticity treatment because of its efficacy, high capability of selective effects and low side effects. In this study, through electrophysiologic tests, mechanisms involved in spasticity reduction following BTX-A injection were studied.
Materials and Methods: This descriptive study was carried out in the year 2006, on 15 hemiplegic patients (age ranged 44- 70 yrs) with spasticity of ankle plantar flexors at Tehran University of medical Sciences. According to the Original Ashworth Scale (OAS), before and after intervention, spasticity of muscles was assessed. Electrophysiologic measurements consisted of amplitude of maximum H- reflex, M response and H / M ratio of soleus muscle, were recorded before and after injection. Toxin was injected in Gastrocnemius (200 units), soleus (75 units) and posterior tibialis muscles (50 unit). Data were recorded in a questionnaire and analyzed by descriptive statistics and frequency distribution tables.
Results: Four weeks after injection, significant reduction in H- reflex, M response amplitudes and H / M ratio were seen. According to the OAS, severity of spasticity also, showed a meaningful reduction. H – Reflex amplitude had more expressive reduction than M response.
Conclusion: Reduction of H -reflex amplitude and H / M ratio is the result of toxin effect on intrafusal fibers and reduction of M response amplitude is the result of toxin effect on extrafusal fibers. More significant reduction of H – reflex amplitude in comparison to M response, showed that BTX-A can reduce the spasticity through modification of gamma motor neuron system. Results of this study could help the therapists, in selecting the most efficient therapeutic exercises, for application after the BTX-A injection.


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