Manuel F. Mas, Sheng Li, Gerard E. Francisco
Department of Physical Medicine and Rehabilitation, University of Texas Health Science Center at Houston McGovern Medical School and TIRR Memorial Hermann, Houston, Texas, USA. E-mail: manuel.mas@uth.tmc.edu
DOI: 10.2340/16501977-2257

Objective: Botulinum neurotoxin is commonly utilized in neurorehabilitation as a treatment for focal spasticity. Clinical experience has yielded observations of late motor recovery after intramuscular injection of botulinum neurotoxin, that are not readily explained by the classical mechanism of action of the neurotoxin in controlling spasticity. These findings have triggered speculation regarding a botulinum neurotoxin mediated effect at the central level after peripheral intervention.
Methods: A review of current literature reveals evidence of distant action after peripheral botulinum neurotoxin injection in affected muscles, be it in other muscles, nerves, spinal cord or the cortex.
Results: Plausible explanations for a centrally mediated late motor recovery after botulinum neurotoxin injection include: (i) direct action of botulinum neurotoxin at distant sites in the central nervous system, mediated by retrograde transport of the neurotoxin into the spinal cord, and (ii) cortical reorganization due to botulinum neurotoxin-induced decrease in peripheral sensory input at the local injection site.
Conclusion: Additional research is required to further elucidate these hypotheses, as well as providing specific dosing specifications, patient selection criteria and the interplay with other therapeutic modalities necessary to promote late motor recovery.

Spasticity, or muscle tightness, can occur after a stroke or brain injury. Injection of botulinum toxin to spastic muscles is a commonly utilized intervention for these findings. We have observed several cases with paralysis and tightness of the hand muscles, years after a stroke, that also recover movement in the injected muscles. This is not readily explained by the usual mechanisms of Botulinum toxin. There is ample evidence that Botulinum toxin may also work at other areas after injection, including the spinal cord and brain. Perhaps, this is how it can appear so long after initial paralysis. Thus, these potential actions should be further studied.