Botulinum toxin treatment of myofascial pain: a critical review of the literature.

This is a review of literature relevant to the treatment of myofascial pain syndrome by botulinum injections. The objective is to critically review the studies to see if they are appropriately designed, conducted, and interpreted to provide guidance in the management of myofascial pain. The intent is to better understand the mixed results that these studies have provided. A search was made utilizing PubMed for literature relevant to the use of botulinum toxin in the treatment of myofascial pain. All identifiable series were reviewed, including open label, single-blinded and double-blinded studies, randomized and controlled, or not. In general, small case series of only a few patients were not included unless they made a relevant point and there were no available randomized studies or larger studies. Single case reports were not included. This is not a meta-analysis. The studies were evaluated according to their design and the selection of outcome measurements, and the interpretation of results. The studies were individually critiqued, and an overall assessment and commentary was made of the studies in the field as a whole. Problems that were common to the studies were robust placebo responders, incomplete treatment of a regional myofascial pain syndrome, inappropriate or confounding control populations or treatments, and inappropriate time periods for assessment of outcomes, or misinterpretation of the time-frame of action of botulinum toxin. The studies of the effect of botulinum toxin treatment of myofascial trigger points have had mixed results. However, few studies have been designed to avoid many of the pitfalls associated with a trial of botulinum toxin treatment of trigger points. Better-designed studies may give results that can be used to guide practice based on reliable evidence. At the present time, one must conclude that the available evidence is insufficient to guide clinical practice.