Discussion
Several studies have shown the efficacy of BoNT-A in treatment of TMD [3,8]. Different types and doses of botulinum toxin used in researches complicate the comparison of conclusions, as do variations in the outcomes measured, the timing and duration of follow-ups and the complexity of the diagnostics and etiologic factors of TMD. In this study, a beneficial effect was achieved with 50 U of BoNT-A. Pain assessment tools revealed that the TMD symptoms of a 53-year-old woman were relieved for at least 22 weeks, with the best therapeutic gain achieved at 11 weeks. The reduction in TMD pain level correlated with the decrease in sleep dysfunction level and the improvement in jaw function. Pain-related worry decreased and some improvements in psychological factors were observed. The increased level of muscle activity as an etiologic factor in this case might support the beneficial effect of the botulinum toxin treatment since muscle relaxation was achieved. The fact that the pain was bothering the patient for years and CNS was exposed to prolonged nociceptive input, the beneficial effect might be explained by the botulinum toxin’s effects on nociceptive neurotransmitters. In future investigations, whether botulinum toxin is effective in preventing pain to progress into a chronic pain condition or whether it is a treatment of choice in chronic pain problem yet should be studied.
The reduced EMG values of the masseter muscle after BoNT-A injections clearly show the physiologic effect of the drug. Before the injections, the AEMG was 241 mV and two weeks later the value had dropped to 55 mV, which is only slightly higher than the AEMG value at rest (45 mV) (Figure 1). A considerable reduction in muscle activity was observed throughout the study, i.e. up to 22 weeks. Decreased bite forces were observed; the mean value obtained before treatment was 580 N, and after the injections the lowest values were seen at 2 weeks (305 N) and 11 weeks (326 N) (Figure 1).
In this case the patient did not experience any adverse effects during 22 months. The temporary side effects reported in the literature are localized pain, difficulty chewing, and focal muscle weakness. [3]. The repeated injections of BoNT-A into the masseter muscle may decrease bone volume in the mandibular angle which emphasizes that a treatment plan should be done judiciously and side effects should be monitored when multiple injections are planned [9]. As with any other treatment modality careful evaluation of etiologic factors of the disorder should be done since only the treatment directed to the source of the pain can lead to a successful result. A re-evaluation of the etiology should take place before repeating the injections.