Muscle Injection in Treating Masseter Myalgia Following TMJ Inflammation Subsided

Objectives: Although pain in the masseter muscle is commonly seen in orofacial pain patients, its treatment is problematic. Clinically, patients often present with the above-mentioned myalgia following initial reduction of TMJ arthralgia after taking NSAIDs. We hypothesize that such myalgia is a result of sensitization process due to inflammation within or around TMJ. This report aims to demonstrate the effect of muscle injections in treating masseter myalgia of such restricted indication. Materials and methods: Patients who met the following criteria were invited to have muscle injection therapy. First visit with pain near TMJ, occurred either near maximal mouth opening or on palpation. The pain should respond well with anti-rheumatic NSAID initially. After further NSAID not resulting in pain reduction, and in masseter muscle presenting painful taught bands, the patient was then sent to experienced physician for muscle injection. If patient hasn't receive injection, muscle self-massage was instructed and served as control. Standard injection technique developed by Dr. Hong C-Z with 1% xylocaine without epinephrine was used. Pressure-pain threshold and visual analog scale (VAS) were used to monitor the treatment outcomes at 20 minutes post-injection, 1 week, 2 weeks, and 1 month follow up. Results: 18 female patients (mean age 30.2 years) received the injection and 10 (mean age 28.8 years) female patients were control. Pressure-pain threshold decreased and VAS showed increase 20 minutes after injection. However on follow-up, pressure-pain threshold significantly increased and the VAS showed a noticeable decrease. These improvements were especially evident after 2 weeks post-injection, and lasted till the end of observation. Control subjects showed minimal changes in pressure-pain threshold and VAS throughout the whole period. Conclusion: Muscle injection is effective, at least short-term in treating masseter muscle pain after TMJ inflammation has subsided.