Review of Botulinum Toxin Uptake and Novel Theory Regarding Potential Spread Days After Injection.

Although most clinicians agree that diffusion of botulinum neurotoxin (BoNT) occurs, its extent, timeline, and clinical importance have been debated. A literature search on PubMed (National Institutes of Health, Bethesda, MD) was done up to January 15, 2023, which included the following search terms: botulinum toxin A uptake; botulinum toxin A diffusion; and botulinum spread. A total of 421 publication titles were found and analyzed. Based on titles, the author selected 54 publications as potentially applicable and reviewed each 1 in depth, along with its supporting references. There are several publications that support a novel theory that small amounts of BoNT can remain in the area days after injection and spread to adjacent muscles. Although current thinking is that BoNT is completely taken up within hours, making its spread days after injection of BoNT not a plausible theory, the following literature review and case report support a novel theory.