I partially agree with the answer given by Khaled Saad but I have to add a clarification about the toxin molecule.

Botulinum toxins may interfere also with pain neurtransmitters, as seeen in headaches.

I think that  the study You are talking about  was led usìng the onabotulinum toxin (botox) but other brands must be used with different dose (abobotulinun toxin Dysport).

Here is an italian study

Pain. 2000 Mar;85(1-2):101-5.

A comparative trial of botulinum toxin type A and methylprednisolone for the treatment of myofascial pain syndrome and pain from chronic muscle spasm.

Porta M. 

And a free recent review

Evid Based Complement Alternat Med. 2013;2013:381459. doi: 10.1155/2013/381459. Epub 2013 Feb 19.

Botulinum toxin for the treatment of myofascial pain syndromes involving the neck and back: a review from a clinical perspective.

Climent JM1, Kuan TS, Fenollosa P, Martin-Del-Rosario F.

Piriformis-syndrome: a mimimum of 50 units Botox/Xeomin or 200 units Dysport,

standard twice as much