Here the result :

We studied the effect of botulinum toxin type A (BTX-A) injections to the scalene muscles on pain in subjects with thoracic outlet syndrome (TOS) in this double-blind, randomized, parallel group trial with follow-up at 6weeks, 3months, and 6months. Thirty-eight patients referred to physiatrists for management of TOS with BTX-A injection were included. One subject was lost to follow-up and all other subjects completed the trial. A 75-unit dose of BTX-A reconstituted with 0.75cc of normal saline was injected to the anterior scalene (37.5units) and middle scalene (37.5units) muscles using electromyographic guidance. The primary outcome measure was pain as measured on a horizontal visual analog scale (VAS) 6weeks-post-injection. Secondary outcomes were paresthesias measured on a VAS and function measured with the Disabilities of the Arm, Shoulder and Hand (DASH) and Short-form 36 (SF-36) questionnaires. For the primary outcome measure of VAS scores for pain at 6weeks, the difference in the means adjusted for baseline VAS scores between placebo and BTX-A was 5.03mm in favor of BTX-A (95% confidence interval -15.7 to 5.7, P=.36). Changes in secondary outcome measures were also not statistically significant. We conclude that BTX-A injections to the scalene muscles did not result in clinically or statistically significant improvements in pain, paresthesias, or function in this population of subjects with TOS.

Copyright © 2011 International Association for the Study of Pain. Published by Elsevier B.V. All rights reserved.

http://www.ncbi.nlm.nih.gov/pubmed/21628084