Scientists and investigators are probing the possibility that botulinum toxins may migrate from the site of injection and may cause unintended effects including weakening adjacent muscles.
As the myriad clinical uses for botulinum toxins continue to expand, scientists examining their mechanism of action in animal models have demonstrated that these neurotoxins may have a measurable effect on muscles adjacent to the injection site. They also have identified pathways by which the toxins may travel in the nervous system and cause distant neurological effects. The findings have emerged as the US Food and Drug Administration (FDA) investigates reports of adverse reactions in patients treated with botulinum toxin that suggest spread of toxin beyond the injection site.
Kuehn BM. Studies, Reports Say Botulinum Toxins May Have Effects Beyond Injection Site. JAMA. 2008;299(19):2261-2263. doi:10.1001/jama.299.19.2261