Assessing the neurophysiological effects of botulinum toxin treatment for adults with focal limb spasticity: a systematic review

Abstract

To examine effectiveness of botulinum toxin therapy (BoNT), accurate quantification of the neurological component of underlying spasticity is needed. Purpose: Systematically identify and summarize literature on neurophysiological methods to test the effectiveness of BoNT, discuss methodological aspects, and recommend best techniques for clinical and research settings. Methods: Electronic databases were searched using specific keywords. Reviews and reference lists were hand-checked to find relevant studies. Studies in adults with focal limb spasticity were included. Results: Over 300 articles were scanned for relevance, and a list of 90 relevant articles was made. After excluding reviews and studies in healthy controls or non-spasticity related BoNT, 22 articles were reviewed. Neurophysiological techniques included electromyography (EMG; n = 11), electrical nerve stimulation (n = 13), transcranial magnetic stimulation (TMS; n = 1), functional magnetic resonance imaging (fMRI; n = 1), reflex threshold (n = 4), Achilles tendon reflex (n = 1), reflex latency (n = 1). Discussion: Maximum M-wave amplitude (M-max) and stretch reflex threshold techniques were successfully used to measure the neurophysiological effects of BoNT and have high test-retest reliability. EMG techniques require effective magnitude normalization techniques and establishing test-retest reliability. Conclusion: Serial electrical nerve stimulation can be incorporated into clinical practice to assist in follow-up. We recommend using M-max and stretch reflex threshold techniques to assess the neurophysiological effects.

Implications for Rehabilitation

• Botulinum toxin decreases muscle tone and is widely used to manage focal limb spasticity.

• Peripheral nerve electrical stimulation to assess the maximal muscle response and stretch reflex threshold are useful ways of assessing the onset and duration of the neurophysiological effect of botulinum toxin.

Keywords::

• botulinum toxin
• EMG
• neurophysiology
• reflex
• spasticity

Acknowledgments

We would like to thank Dr. Dina Brooks for reviewing the manuscript and for her feedback and comments.

Declaration of interest: The authors report no conflicts of interest. This project was funded through the West Park Foundation, Toronto, Ontario, Canada.