Botulinum toxin type A and acupuncture for masticatory myofascial pain: a randomized clinical trial

Masticatory myofascial pain (MMP) is one of the most common causes of persistent facial pain, affecting between 10% and 68% of people with temporomandibular disorder. This randomized controlled trial investigated the comparative efficacy of two promising therapeutic approaches: traditional acupuncture and botulinum toxin type A (BoNT-A) injections for the treatment of this debilitating condition. The research was conducted by Brazilian researchers from respected institutions, including the University of São Paulo and the University of Campinas, following rigorous ethical and methodological standards. The study included 54 women with a confirmed diagnosis of temporomandibular myofascial pain, who were randomly divided into three groups of 18 participants each.

The acupuncture group received four weekly sessions of traditional Chinese acupuncture lasting 20 minutes each, using specific points such as LI-4, LI-11, SI-19, LR-2, GB-20, GB-21, GB-34, BL-2, CV-23, and TE-23. The botulinum toxin group received bilateral injections with 30 units in the masseter muscle and 10 units in the anterior temporalis. The control group received saline injections at the same locations. Evaluation included measures of self-perceived pain through the visual analog scale, pressure pain threshold by digital algometry, and electromyographic activity of the masticatory muscles.

All measurements were performed before treatment and one month after the start of therapy. The results revealed that all three groups showed significant reduction in self-perceived pain after one month (p < 0.001). Interestingly, there was no statistically significant difference between acupuncture and botulinum toxin in pain reduction (p = 0.05), but both approaches were superior to the control group (p < 0.05). However, only the group that received botulinum toxin showed significant improvement in pressure pain threshold, indicating a reduction in pain sensitivity.

An important finding was that botulinum toxin caused a severe reduction in electromyographic activity of the treated muscles, which should be considered an adverse effect, as it may result in temporary muscle weakness. This effect was not observed with acupuncture, suggesting an advantage of this approach in terms of safety. The mechanisms of action differ between the treatments: botulinum toxin acts by blocking the release of acetylcholine at the neuromuscular junction and inhibiting pain neurotransmitters, while acupuncture modulates pain through peripheral and central inhibition mechanisms. The clinical implications are significant.

The study suggests that both acupuncture and botulinum toxin can be valid options for patients with masticatory myofascial pain refractory to conservative treatments. Acupuncture may be preferable as a first-line treatment due to the lower risk of adverse effects, while botulinum toxin may be reserved for more severe or refractory cases. The similar efficacy between treatments offers clinicians and patients therapeutic options based on individual preferences, specific contraindications, and resource availability. The study presents important limitations, including only one month of follow-up, exclusive inclusion of women, and the lack of evaluation of psychosocial factors that may influence pain chronification.

Future studies with longer follow-up time and more diverse populations will be necessary to confirm these findings.