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.