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Physiological effects of botulinum toxin in spasticity
1Department of Neurology, The Mount Sinai Medical Center, New York, New York 10029-6574, USA. jean-michel.gracies@mssn.edu
Summary
Botulinum toxin (BTX) injections reduce passive movement resistance in spastic muscles. Emerging evidence suggests BTX may also improve active limb function by targeting central nervous system pathways and muscle imbalances.
Area of Science:
- Neuroscience
- Rehabilitation Medicine
- Pharmacology
Background:
- Botulinum toxin (BTX) injections are established for reducing spastic overactivity and passive resistance.
- Improving active performance in paretic limbs remains a significant challenge in BTX therapy for spastic paralysis.
Purpose of the Study:
- To review the neurophysiological mechanisms of BTX beyond neuromuscular blockade.
- To explore how these mechanisms may enhance active movement in spastic paralysis.
- To examine evidence for BTX's effects on spastic cocontraction, weakness, dystonia, and muscle shortening.
Main Methods:
- Review of existing literature on BTX neurophysiology and clinical effects.
- Analysis of data on central nervous system effects of BTX, including axonal transport and synaptic actions.
- Examination of studies reporting BTX-induced changes in muscle activity and joint mechanics.
Main Results:
- BTX exhibits central nervous system effects, including reduced motoneuronal excitability and altered synaptic inhibition.
- Evidence suggests BTX can reduce spastic cocontraction in both injected and antagonist muscles.
- BTX may improve antagonist weakness and reduce spastic dystonia, potentially lengthening shortened muscles.
Conclusions:
- Non-neuromuscular actions of BTX likely contribute to improved active movements in spastic paralysis.
- Targeting spastic antagonists with BTX may address key impairments like weakness, cocontraction, dystonia, and shortening.
- BTX therapy holds potential for comprehensive functional improvement in spastic limbs.