| Summary: | Myofascial pain syndrome (MPS) is described as distinct type of regional musculoskeletal pain complaint that is caused by myofascial trigger points (TrPs) within muscles or their fascia. The trigger is identified as the presence of a taut band in the muscle, tenderness on compression in a point of the band. There are variable estimates from epidemiologic studies on the incidence and prevalence of MPS due to the lack of universally accepted diagnostic criteria for the syndrome, in addition most of the epidemiologic data available pertain to musculoskeletal pain in general. It has been estimated that in a general internal medicine practice 30% of patients complained primarily from myofascial pain, and that for 85% of patients admitted to a comprehensive pain center the primary diagnosis was myofascial pain. Treatment of MPS involves treatment of TrPs and the removal of causative/perpetuating factors. Muscle stretch, TrP injection (such as injection of botulinum toxin, or anaesthetic), acupuncture, therapeutic ultrasound, and drug therapy are treatments currently adopted for the deactivation of TrPs. Correction of perpetuating factors include amending incorrect muscle activity and any abnormal postural issues, as well as, where possible, correcting all possible anatomical defects causing muscle imbalance. Botulinum Toxin A (BoNTA) is a purified neurotoxin complex produced from the fermentation of Clostridium botulinium type A. BoNTA inhibits acetylcholine release into the neuromuscular junction, resulting in reduction in muscular contractions. In Canada BoNTA is marketed in three distinct formulations, Botox, Dysport, and Xeomin. BoNTA is used off-label for the treatment of MPS. The objective of this review is to evaluate the clinical effectiveness of BoNTA in the treatment of MPS. This report is an update to a CADTH Rapid Response report published in October 2008
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