Botulinum toxin injection for management of thoracic outlet syndrome: a double-blind, randomized, controlled trial

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 6 weeks, 3 months, and 6 months. 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 0.75 cc of normal saline was injected to the anterior scalene (37.5 units) and middle scalene (37.5 units) muscles using electromyographic guidance. The primary outcome measure was pain as measured on a horizontal visual analog scale (VAS) 6 weeks-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 6 weeks, the difference in the means adjusted for baseline VAS scores between placebo and BTX-A was 5.03 mm 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.