Effectiveness, Safety, and Predictors of Response to Botulinum Toxin Type A in Refractory Masticatory Myalgia: A Retrospective Study.

[PURPOSE] Masticatory muscle pain disorders respond well to conservative therapy; however, in some patients the pain becomes refractory. Botulinum toxin type A (BoT-A) therapy has been shown to be an effective modality in the management of refractory headache disorders. Conversely, there are conflicting reports in the literature regarding the efficacy, safety, and predictors of therapeutic response to BoT-A therapy for management of refractory masticatory muscle pain.

[MATERIALS AND METHODS] We performed a retrospective chart review of patients who underwent at least 2 injection cycles of 100 U of BoT-A for refractory masticatory myalgia in the Department of Oral and Maxillofacial Surgery, Massachusetts General Hospital, between May 2012 and June 2016. Information regarding demographic, diagnostic, and therapeutic characteristics was extracted and analyzed. The χ test was used for analysis between independent and dependent variables. Forward step-wise-type logistic regression analysis was conducted to determine the predictors of outcome.

[RESULTS] Among 116 participants, 30.6% reported significant relief in pain for a mean period of 10.1 weeks. A total of 16.4% of participants reported at least 1 adverse effect. The effectiveness of the BoT-A therapy was found to be statistically associated with the presence of muscle hypertrophy (P = .004), range of motion (P = .02), concurrent use of opioid analgesics (P = .003), and local anesthetic trigger-point injections (P = .003). Logistic regression analyses suggested that the presence of muscle hypertrophy and occurrence of adverse effects were predictors of positive outcome. On the contrary, concurrent use of opioid analgesics was found to be a predictor for no or minimal relief.

[CONCLUSIONS] BoT-A therapy provides significant relief for approximately one third of patients with refractory masticatory muscle pain. Therapy is associated with a mild risk of adverse effects. The presence of muscle hypertrophy, occurrence of an adverse effect, and concurrent use of opioid analgesics were found to be predictors of outcome response.