Change of stretch reflex threshold in spasticity: effect of botulinum toxin injections

摘要

Spasticity is a motor disorder characterised by a velocity-sensitive increase in stretch reflex with exaggerated jerk reflex as a component of upper motor neuron disease (10). This kind of muscle hypertonia is an outcome of many neurological lesions. In particular it occurs after lesion of corticospinal pathways, which are inhibitory on stretch reflex circuit. The normal control of posture is mediated by interactions between descending spinal pathways, which are either inhibitory (as the reticulospinal projections) or excitatory (as the vestibulospinal projections) on motoneurones innervating antigravitary muscles (14), which are the muscles undergoing to spasticity after lesions. An increased excitation on these motoneurons can be the result of lesions, both of the reticulospinal pathway, as after spinal cord injury, and of the cortical and subcortical structures, as stroke or head injury, which result in a disfacilitation of inhibitory reticulospinal pathways.