RESUMEN
The purpose of this study was to evaluate the analgesic effect of botulinum toxin A (BoNTA) injections in patients with myofascial pain syndrome (MPS) who were previously treated with the local infiltration of anesthetic and steroids (LIAS). The study included a retrospective phase and a longitudinal open-label prospective phase, which were conducted on consecutive patients with MPS previously treated with the local infiltration of anesthetic (levobupivacaíne 0.25%) and steroids (triamcinolone 40 mg). Eligible patients were treated with a single intramuscular injection of BoNTA (Botox; Allergan, Inc., Irvine, CA). The treatment efficacy was determined according to the degree of pain relief obtained. Eighty-two patients met the inclusion/exclusion criteria and were included in the study. Successful results were obtained for 32 (39.0%) and 30 (36.6%) patients, during treatment with BoNTA and LIAS, respectively. The mean (standard deviation) length of the analgesic effect was significantly longer with BoNTA (29.6 [SD = 17.7] weeks) than with LIAS (8.5 [SD = 6.4] weeks), P <.0001. As regards the side effects, 19 (23.2%) patients reported transient soreness at the injection site for 2 to 3 days with BoNTA. The MPS patients previously treated with a local infiltration of anesthetic and steroids who then received a single injection of BoNTA experienced significantly reduced pain for a relatively long time.