Introduction.
Botulinum toxin inhibits
acetylcholine (ACh) release and probably blocks some nociceptive
neurotransmitters. It has been suggested that the development of myofascial trigger points (MTrP) is related to an excess release of ACh to increase the number of sensitized nociceptors. Although the use of
botulinum toxin to treat
myofascial pain syndrome (MPS) has been investigated in many clinical trials, the results are contradictory. The objective of this paper is to identify sources of variability that could explain these differences in the results. Material and Methods. We performed a content analysis of the clinical trials and systematic reviews of MPS. Results and Discussion. Sources of differences in studies were found in the diagnostic and selection criteria, the muscles injected, the injection technique, the number of trigger points injected, the dosage of
botulinum toxin used, treatments for control group, outcome measures, and duration of followup. The contradictory results regarding the efficacy of
botulinum toxin A in MPS associated with neck and
back pain do not allow this treatment to be recommended or rejected. There is evidence that
botulinum toxin could be useful in specific myofascial regions such as
piriformis syndrome. It could also be useful in patients with refractory MPS that has not responded to other myofascial injection
therapies.