Our sincere thanks to Dr. Susan Herring of the University of Washington in Seattle  for providing the following summary of a recent article in the profressional journal, Pain.

Efficacy of botulinum toxin type A for treatment of persistent myofascial TMD pain: a randomized, controlled, double-blind multicenter study
Ernberg M., Hedenberg-Magnusson B., List T., Svensson P.
In press, Pain (2011), doi:10.1016/j.pain.2011.03.036.
 
Botox blocks the release of neurotransmitters from nerve endings.  Although chiefly used to stop muscle contraction, it might also relieve pain by preventing nerves from releasing inflammatory molecules. This clinical trial investigated whether Botox injection of the masseter was an effective treatment for patients with persistent myofascial TMJ pain.
 
The 21 patients (19 female) all met rigorous criteria and were recruited from 4 Danish and Swedish clinics. The study was very well-controlled in that (1) patients served as their own controls and were injected twice, once with Botox and once with saline, but in random order (crossover design) and (2) investigators as well as subjects were blinded as to which substance was injected (double blinding).  Patients were carefully examined for pain and other variables 1 month and 3 months after the injections.

Side effects reported in the first week after injections included headache and fatigue, but were similar for Botox and saline; side effects were gone by 1 month. This suggests that subjects were not able to tell which injection was the Botox.

Surprisingly, pain intensity was reduced after both Botox and saline injections, although more so for Botox.  However, the number of patients that experienced significant (defined as 30% decrease) pain reduction was about the same for both treatments.

The investigators concluded that there was a strong placebo effect, which means that less well-controlled studies may not be valid. While there was a slightly better outcome for Botox than for saline, it was small and was not experienced by all patients.  The authors recommended against the use of Botox as an adjunct to conservative treatment of persistent myofascial pain on the basis of its high cost and lack of efficacy.