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

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.