I found this study online yesterday from the 'World Journal of Gastrointestinal Surgery'. There's quite a bit of interesting stuff in it which is worth a read. Anyhow, here's the link to the pdf file:
http://www.drofrx.com/Notes_files/anal% ... e%20Tx.pdf
Another interesting page on a botox alternative, Gonyautoxin:
https://www.ncbi.nlm.nih.gov/pubmed/15812585