The effect of small doses of botulinum toxin A on neck-shoulder myofascial pain syndrome: A double-blind, randomized, and controlled crossover trial

Objectives: Myofascial pain syndrome is a common cause of muscular pain in the shoulder-neck region. Injections of large amounts of botulinum toxin A have been found to be beneficial for the alleviation of myofascial pain, but large doses of this toxin may cause paresis of the muscle and other adverse events. The aim of this work was to determine the effect of small doses (5 U) of botulinum toxin A (BTA) injected directly into the painful trigger points of the muscles, using a double-blind crossover technique. Methods: On the basis of the empirical criteria proposed for diagnosis of myofascial pain syndrome, 31 patients suffering from myofascial pain in the neck-shoulder region were studied. The patients received either botulinum toxin A or physiological saline injections on 2 occasions 4 weeks apart. The total dose varied from 15 to 35 U of botulinum toxin A [28 +/- 6 U (mean SD)]. The follow-up measurements were carried out at 4 weeks after each treatment. Neck pain and result of treatment were assessed with questionnaires. The pressure pain threshold was determined using a dolorimeter. Results: Neck pain values decreased from 4.3 +/- 2.4 to 3.3 +/- 2.0 after saline injections and from 4.1 +/- 2.1 to 3.3 +/- 2.2 after botulinum toxin A. The pressure pain threshold values increased from 5.2 +/- 1.6 to 5.9 +/- 1.5 and from 5.7 +/- 1.6 to 5.9 +/- 1.6 after injections with saline and botulinum toxin A, respectively. No statistically significant changes in the neck pain and pressure pain threshold values occurred between the botulinum toxin A and saline groups. After the first injections, the subjective result of treatment was significantly (P = 0.008) in favor of botulinum toxin A, and after the second injections, the subjective result was better for saline, but the difference was not statistically significant (P = 0.098). There was no significant difference in the prevalence of side effects between saline and botulinum toxin A.