Article

The therapeutic effects of intramuscular injections of botulinum
toxin-type A on spasticity can largely be explained by its blocking action at the
neuromuscular junction. Botulinum toxin-type A is also thought to have a central
action on the functional organization of the central nervous system. This study
assessed the action of botulinum toxin-type A on spinal motor networks by
investigating post-activation depression of the soleus H-reflex in post-stroke
patients. Post-activation depression, a presynaptic mechanism controlling the
synaptic efficacy of Ia-motoneuron transmission, is involved in the
pathophysiology of spasticity. PATIENTS: Eight patients with chronic hemiplegia
post-stroke presenting with lower limb spasticity and requiring botulinum
toxin-type A injection in the ankle extensor muscle. METHODS: Post-activation
depression of soleus H-reflex assessed as frequency-related depression of
H-reflex was investigated before and 3, 6 and 12 weeks after botulinum toxin-type
A injections in the triceps surae. Post-activation depression was quantified as
the ratio between H-reflex amplitude at 0.5 and 0.1 Hz. RESULTS: Post-activation
depression of soleus H-reflex, which is reduced on the paretic leg, was affected
3 weeks after botulinum toxin-type A injection. Depending on the residual motor
capacity of the post-stroke patients, post-activation depression was either
restored in patients with preserved voluntary motor control or further reduced in
patients with no residual voluntary control.
CONCLUSION: Botulinum toxin
treatment induces synaptic plasticity at the Ia-motoneuron synapse in post-stroke
paretic patients, which suggests that the effectiveness of botulinum toxin-type A
in post-stroke rehabilitation might be partly due to its central effects.

Langue : ANGLAIS