Mechanisms of action of phenol block and botulinus toxin type A in relieving spasticity - Electrophysiologic investigation and follow-up

This preliminary study was designed to investigate the effects of botulinus toxin Type A and phenol treatments on electrophysiologic tests evaluating spinal afferent and efferent melter pathways involved in spasticity. The qu estions posed were whether different types of mechanisms act on reducing sp asticity with these different treatment modalities and whether the tests ar e correlated with clinical recovery. Twenty patients with lower limb spasti city secondary to stroke were randomly assigned to receive 400 mouse units of botulinus toxin Type A injected into the calf muscles or to receive a ti bial nerve blockade with 3 mi of 5% phenol. The amplitudes of the Achilles tendon response, M response, H reflex response, and maximum H:M ratio and A chilles tendon response to H response ratio were recorded from the soleus m uscle at baseline and at Weeks 2, 4, and 12. The most obvious change was a reduction in the amplitude of the tendon response in the group that receive d botulinus toxin Type A, and it was a reduction in the M response amplitud e in the group that received phenol. The decrease in the tendon response am plitude and tendon response to H ratio in the group that received botulinus toxin Type A and the decrease in the M response amplitude in the phenol gr oup were found to be well correlated with clinical recovery as assessed by the Ashworth scale. The findings suggested that botulinus toxin Type A inje ction decreases spasticity primarily by affecting the fusimotor system and muscle spindle, and the involvement of the a-motor fibers within the tibial nerve is the most likely factor contributing to the reduction of spasticit y after phenol blockade. The therapeutic effectiveness of these agents coul d be assessed and followed up by the changes in electrophysiologic response s matching their mechanisms of action. The findings should be supported by further electrophysiologic techniques.