Use of botulinum toxin in the treatment of chronic myofascial pain

Background: Myofascial pain syndrome (MPS) is defined as acute or chronic pain with sensory or motor autonomic symptoms, referred from active myofascial triggering points with associated dysfunction. Previous studies have suggested the usefulness of botulinum toxin A (BTX-A) in the treatment of MPS since it is capable of controlling muscular spasms, as well as other alternative mechanisms of action. Objectives: To analyze the efficacy of BTX-A treatment and its effect on daily life activities assessing pain reduction using a visual analogue scale (VAS); degree of improvement in physical impairment and disability scoring in the Oswestry low back pain questionnaire; and psychologic status using the Hospital Anxiety and Depression Scale (HAD), in patients suffering from MPS. Method: An open-label interventional prospective trial was conducted in 77 patients diagnosed of refractory MPS (defined as the presence of muscle spasm with pain on mobilization or stretching, plus the existence of trigger points with associated referred pain), resistant to both conservative management and to physical therapy. The BTX-A dosages for the different muscles were chosen according to a standardized protocol. Electromyographic guidance was used to localize the motor end plate prior to injection in superficial muscles; while fluoroscopic guidance was employed to evidence intramyofascial spread of the contrast solution within deep muscles. The assessment of treatment efficacy was based on a pain VAS applied before enrollment, at 15, 30, and 90 days and upon completion of the study; the Lattinen test to establish a relationship between pain intensity and its corresponding impact on daily living; and the HAD scale to assess psychologic stress, performed both before treatment and at the end of the study; and the Oswestry Questionnaire was used to evaluate patients' ability to carry out daily life activities according to their degree of physical impairment and disability scores. Results: The global analysis revealed a positive correlation between the VAS score prior to treatment and the scoring at 15, 30, and 90 days. This correlation was maintained when analyzing independently for superficial or deep muscles. The correlation coefficients for HAD scores and the Lattinen test values showed a significant association between pre- and post-treatment findings. No adverse events were recorded for 83.1% of the cases. Conclusions: The results of this study are consistent with other studies showing the efficacy of BTX-A for treating pain in MPS. The evaluation of the psychologic dimension of this disorder and its associated disability can provide valuable information for the adequate management of these patients and for assessing treatment outcome.